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ToSeek
2005-Jul-05, 02:13 PM
I think it would be nice to have a thread dedicated reports on the science findings from the Deep Impact collision. I'll start it off with XMM-Newton detects water in comet (http://spacenews.dancebeat.info/article.php/xmm-newton_detects_water_tempel_1), as initially mentioned (http://www.badastronomy.com/phpBB/viewtopic.php?p=497429#497429) by the BA.

ToSeek
2005-Jul-05, 04:37 PM
Crash Course in Comet Construction (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid= 1632&mode=thread&order=0&thold=0)


Comet Tempel 1 was hit hard by a NASA spacecraft earlier today. Deep Impact scientists provided more details about what the impact has taught us about the comet's structure.

Swift
2005-Jul-05, 06:23 PM
Crash Course in Comet Construction (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid= 1632&mode=thread&order=0&thold=0)



A'Hearn says that Tempel 1 looks different from comets Wild 2 and Borrelly, and they're scratching their heads, trying to figure out why.

"When Wild 2 looked different from comet Borrelly, we thought it might be due to the different orbital histories of the two comets," says A'Hearn. "But this comet's had an orbital history that we think is pretty much similar to Borrelly, and yet it looks totally different. So there's something more going on here that we haven't understood yet."

I take the difference in orbital histories to mean what happened to the various comets since their formation (how close or far they are from the sun and how much they have been heated). I wonder if the remaining differences can be explained by differences in the formation phase? Do current models of solar system formation predict that all the cometary material would be relatively identical, or would you expect a certain amount of variation? My un-educated guess would be the latter.

CJSF
2005-Jul-05, 06:28 PM
A'Hearn says that Tempel 1 looks different from comets Wild 2 and Borrelly, and they're scratching their heads, trying to figure out why.

"When Wild 2 looked different from comet Borrelly, we thought it might be due to the different orbital histories of the two comets," says A'Hearn. "But this comet's had an orbital history that we think is pretty much similar to Borrelly, and yet it looks totally different. So there's something more going on here that we haven't understood yet."

I don't know. While there are clearly differences, I was thinking about how Tempel 1 looked like a cross between Borrelly and Wild 2. I didn't see anything so different among the three that made me think they weren't the same class of objects.

CJSF

John Kierein
2005-Jul-05, 07:07 PM
From the Boulder Daily Camera. You may have to register? Or not.

http://tinyurl.com/a5qv4

Has unusual white areas on the surface.

Paladin
2005-Jul-05, 07:33 PM
disregard

ToSeek
2005-Jul-05, 08:52 PM
I would prefer that this thread remain focused on genuine scientific findings. There are plenty of other Deep Impact threads for discussing other issues. This one (http://www.badastronomy.com/phpBB/viewtopic.php?t=22737) is probably the best for discussing, um, unconventional theories.

publiusr
2005-Jul-06, 09:21 PM
Not along that line--but could the probe have put a minor amount of back spin on the body due to a hit on the edge(if not changing its course in the slightest)?

Superluminal
2005-Jul-07, 02:02 AM
The change in velocity was expected to be so slight, something like .0014 meters per second, (IIRC) I doubt very seriously it put any back spin on it.

I just finished looking at old Astronomy articles about the SL9 impact on Jupiter. The leading model was that the comet fragments tunneled through the outer atmosphere before exploding, and the fireball traveled back out the tunnel before expanding. From looking at the impact movie from the flyby craft something similar happened on Temple. Except that instead of atmosphere the probe traveled some distance through a soft surface before impacting a solid surface.

The XMM-Newton team claimed a solid surface impact based on the amount of ultraviolet light observed at impact. But the thin shadow seen in the movie just after impact and before the plume began to spread out seem, to me anyway, to support the soft then solid surface impact.

Could that indicate that the upper surface wasn't just soft but was very fluffy? What would the investigators look for in the spectra to confirm that it was soft?

Kullat Nunu
2005-Jul-07, 07:19 PM
Universe Today: Gemini Sees Rocky Material on Tempel 1 (http://www.universetoday.com/am/publish/deep_impact_gemini.html?772005)

publiusr
2005-Jul-07, 07:28 PM
I hear about two layers--a soft layer and a harder layer IIRC.

ToSeek
2005-Jul-08, 04:23 PM
Odin's first post-hit water measurements of Tempel 1 (http://www.ssc.se/default.asp?groupid=2004517104342856)


The first measurements by Odin of water vapour from the comet Tempel 1 after the Deep Impact hit are now available. The figure (click for full picture) shows four measurements at different occasions, 7 hours before impact and 5, 17, and 32 hours after. The scientist are now busy trying to interpret these measurements to understand what happened to the outgassing of water from the comet.

ToSeek
2005-Jul-08, 06:41 PM
Scientists Measure How Deep "Deep Impact" Was, With X-rays (http://www.spaceref.com/news/viewpr.html?pid=17373)


Here come the X-rays, on cue. Scientists studying the Deep Impact collision using NASA's Swift satellite report that comet Tempel 1 is getting brighter and brighter in X-ray light with each passing day.

The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet's thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.

Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.

"Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source," said Dr. Paul O'Brien of the Swift team at the University of Leicester. "How things change when you ram a comet with a copper probe traveling over 20,000 miles per hour. Most of the X-ray light we detect now is generated by debris created by the collision. We can get a solid measurement of the amount of material released."

Manchurian Taikonaut
2005-Jul-08, 10:21 PM
great pictures from the mission & very good data :D

ToSeek
2005-Jul-09, 01:24 AM
News Release: 2005-113 July 8, 2005



NASA’s Deep Impact Tells a Tale of the Comet



Data from Deep Impact's instruments indicate an immense cloud of fine powdery material was released when the probe slammed into the nucleus of comet Tempel 1 at about 10 kilometers per second (6.3 miles per second or 23,000 miles per hour). The cloud indicated the comet is covered in the powdery stuff. The Deep Impact science team continues to wade through gigabytes of data collected during the July 4 encounter with the comet measuring 5-kilometers-wide by 11-kilometers-long (about 3-miles-wide by 7-miles-long).



"The major surprise was the opacity of the plume the impactor created and the light it gave off," said Deep Impact Principal Investigator Dr. Michael A'Hearn of the University of Maryland, College Park. "That suggests the dust excavated from the comet's surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets -- an ice cube."



How can a comet hurtling through our solar system be made of a substance with less strength than snow or even talcum powder?



"You have to think of it in the context of its environment," said Dr. Pete Schultz, Deep Impact scientist from Brown University, Providence, R.I. "This city-sized object is floating around in a vacuum. The only time it gets bothered is when the Sun cooks it a little or someone slams an 820-pound wakeup call at it at 23,000 miles per hour."



The data review process is not overlooking a single frame of approximately 4,500 images from the spacecraft's three imaging cameras taken during the encounter.



"We are looking at everything from the last moments of the impactor to the final look-back images taken hours later, and everything in between," added A'Hearn. "Watching the last moments of the impactor's life is remarkable. We can pick up such fine surface detail that objects that are only four meters in diameter can be made out. That is nearly a factor of 10 better than any previous comet mission."



The final moments of the impactor's life were important, because they set the stage for all subsequent scientific findings. Knowing the location and angle the impactor slammed into the comet's surface is the best place to start. Engineers have established the impactor took two not unexpected coma particle hits prior to impact. The impacts slewed the spacecraft's camera for a few moments before the attitude control system could get it back on track. The penetrator hit at an approximately 25 degree oblique angle relative to the comet's surface. That's when the fireworks began.



The fireball of vaporized impactor and comet material shot skyward. It expanded rapidly above the impact site at approximately 5 kilometers per second (3.1 miles per second). The crater was just beginning to form. Scientists are still analyzing the data to determine the exact size of the crater. Scientists say the crater was at the large end of original expectations, which was from 50 to 250 meters (165 to 820 feet) wide.



Expectations for Deep Impact's flyby spacecraft were exceeded during its close brush with the comet. The craft is more than 3.5 million kilometers (2.2 million miles) from Tempel 1 and opening the distance at approximately 37,000 kilometers per hour (23,000 miles per hour). The flyby spacecraft is undergoing a thorough checkout, and all systems appear to be in excellent operating condition.



The Deep Impact mission was implemented to provide a glimpse beneath the surface of a comet, where material from the solar system's formation remains relatively unchanged. Mission scientists hoped the project would answer basic questions about the formation of the solar system by providing an in-depth picture of the nature and composition of comets.

The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena, Calif.

For information about Deep Impact on the Internet, visit:

<http://www.kintera.org/TR.asp?ID=M69842575956263916425265>www.nasa.gov/deepimpact

Saluki
2005-Jul-09, 01:57 AM
Is there any further science the flyby craft can do when it is out of range of the comet?

01101001
2005-Jul-09, 02:06 AM
Is there any further science the flyby craft can do when it is out of range of the comet?
Yes (http://www.badastronomy.com/phpBB/viewtopic.php?p=498524#498524), if they send it to examine another comet.

01101001
2005-Jul-09, 03:00 AM
Comet Tempel's Silhouette (http://photojournal.jpl.nasa.gov/catalog/PIA02139)

http://photojournal.jpl.nasa.gov/thumb/PIA02139.jpg (http://photojournal.jpl.nasa.gov/catalog/PIA02139)


The colors represent brightness, with white indicating the brightest materials and black showing the faintest materials. This brightness is a measure of reflected sunlight. [...] The large plume of dust that was kicked up upon impact can be seen as the colorful, drop-shaped object. This plume was very bright, indicating that the comet's surface material must be very fine, like talcum powder.

01101001
2005-Jul-09, 09:49 AM
Harvard-Smithsonian Center for Astrophysics, Press Release: Deep Impact Was a Dust-up, Not a Gusher (http://www.cfa.harvard.edu/press/pr0523.html)


Results are still coming in, but so far the scientists report seeing only weak emission from water vapor and a host of other gases that were expected to erupt from the impact site. The most conspicuous feature of the blast was brightening due to sunlight scattered by the ejected dust. [...] SMA measurements corroborate the SWAS findings. Although the SMA wasn't tuned to frequencies of water emission, which are difficult to observe from the ground due to atmospheric water vapor, it watched for other chemicals such as hydrogen cyanide. SMA astronomers saw little increase in production of gases following the impact. Gas production rates remained so low that they could set only an upper limit on the total. [...] Qi added that the comet might become more active over the following days and weeks. "We're still hoping for a big outgassing from the new active area created by Deep Impact. If we see any signs of that, we'll make more observations."

ToSeek
2005-Jul-12, 04:37 PM
Summary of findings from several sources:

Deep Insight: Comet Buster Reveals Dusty Secrets (http://www.space.com/scienceastronomy/050712_deep_insight.html)


Hot vapor containing water and carbon dioxide was detected by Deep Impact's flyby instrument. Researchers continue to comb through the mountains of data looking for other comet ingredients, while space- and ground-based telescopes monitor the collision aftermath from afar.

ToSeek
2005-Jul-19, 04:22 PM
Deep Impact may never glimpse comet crater (http://www.newscientistspace.com/article/dn7688)


NASA's Deep Impact may fail to live up to its billing as the first mission to look inside a comet. Computer processing designed to correct the spacecraft's defocused camera cannot fully correct the images taken just after impact. If the situation cannot be rectified, there will be no way of seeing the newly formed crater - one of the mission's major goals.

Manchurian Taikonaut
2005-Jul-20, 10:23 AM
Summary of findings from several sources:

Deep Insight: Comet Buster Reveals Dusty Secrets (http://www.space.com/scienceastronomy/050712_deep_insight.html)


Hot vapor containing water and carbon dioxide was detected by Deep Impact's flyby instrument. Researchers continue to comb through the mountains of data looking for other comet ingredients, while space- and ground-based telescopes monitor the collision aftermath from afar.

what a great mission 8)

Grey
2005-Jul-20, 04:01 PM
Deep Impact may never glimpse comet crater (http://www.newscientistspace.com/article/dn7688)
:(

Superluminal
2005-Jul-21, 11:09 PM
Since it looks like we are in for a long wait before the peer reviewed papers will be coming out, has anyone speculated on what the differant geological features on the nucleus may be.
http://photojournal.jpl.nasa.gov/jpegMod/PIA02127_modest.jpg

In the area near where the probe impacted are what appear to be two normal looking impact craters. Just above and to the left is a smooth area that looks like something may have flowed from a crater on the terminator.

In the upper part of the image is what looks to me like a sinkhole with a bright smaller area in it. A possible jet that left bright fresh material behind? Anyone know where the active areas are in relation to what we are looking at?

Just above that depression, is another smooth area, similar in appearance to the above mentioned flow. But it is round and looks like it is uplifted a little. Could it be an upwelling similar to a volcanic dome before an eruption?

Just some of my very unproffessional observations.

2005-Jul-22, 01:29 AM
Since it looks like we are in for a long wait before the peer reviewed papers will be coming out, has anyone speculated on what the differant geological features on the nucleus may be.
http://photojournal.jpl.nasa.gov/jpegMod/PIA02127_modest.jpg

In the area near where the probe impacted are what appear to be two normal looking impact craters. Just above and to the left is a smooth area that looks like something may have flowed from a crater on the terminator.

In the upper part of the image is what looks to me like a sinkhole with a bright smaller area in it. A possible jet that left bright fresh material behind? Anyone know where the active areas are in relation to what we are looking at?

Just above that depression, is another smooth area, similar in appearance to the above mentioned flow. But it is round and looks like it is uplifted a little. Could it be an upwelling similar to a volcanic dome before an eruption?

Just some of my very unproffessional observations.

And what about the ridges that come together towards the right near the bottom ... sort of a ">" shape? Pressure ridges?

Superluminal
2005-Jul-22, 02:10 AM
I don't know. The whole upper half of the nucleus looks like it's partly melted and is slowly oozing towards the lower part of the image.

01101001
2005-Aug-23, 11:54 PM
It's kind of weird, but the NASA Deep Impact home page (http://www.nasa.gov/mission_pages/deepimpact/main/index.html) announces on August 22, a Deep Impact Mission update:


Deep Impact Mission Update
08.22.05 -- Ever since Deep Impact's spectacularly successful collision with comet Tempel 1, Principal Investigator Michael A'Hearn and mission colleagues at the University of Maryland and seven other institutions have been working at top speed to analyze the huge amount of raw data collected during the brief encounter. The mission's principal findings will be published in a September issue of the journal Science.

The weird part is that the linked Univeristy of Maryland article (http://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1114) has a date of August 22 on it, but uses August 5 in the headline.

Anyway, the key timeline events for mission data seem to be these:


The mission's principal findings will be published in a September issue of the journal Science.


In keeping with the mission's long-planned schedule, the full set of raw and calibrated data from the mission will be delivered to NASA's Planetary Data System in January 2006.

ToSeek
2005-Sep-06, 06:20 PM
Analysis: Deep Impact Comet All Fluff (http://www.space.com/scienceastronomy/050906_tempel1_update.html)


The shape and surface features of the comet rammed this summer by NASA's Deep Impact (http://www.space.com/deepimpact/) probe are quite different from the two other comets whose cores have been studied, scientists said today.

Comet Tempel 1, hit (http://www.space.com/scienceastronomy/050705_scitues_deepimpact.html) in early July by an 820-pound probe, appears to be coated with fine powder rather than solid ice and rock. The powder is even finer than sand, scientists had reported shortly after the impact.

A thorough analysis confirms that and other preliminary conclusions about the 7-mile-long icy world, which appears to be rather fluffy.

R.A.F.
2005-Sep-06, 06:32 PM
Fluffy?? Wasn't it supposed to clang like a bell?? :) :)

(Sorry, I couldn't resist.)

ToSeek
2005-Sep-06, 06:32 PM
Deep Impact Adds Color to Unfolding Comet Picture (http://www.physorg.com/news6258.html)


"Prior to our Deep Impact experiment, scientists had a lot of questions and untested ideas about the structure and composition of the nucleus, or solid body of a comet, but we had almost no real knowledge," said Deep Impact principal investigator Michael A'Hearn, a professor of astronomy at the University of Maryland, College Park, Md. "Our analysis of data produced by Deep Impact is revealing a great deal, much of it rather surprising."

VanderL
2005-Sep-06, 07:06 PM
Thanks ToSeek,

You better change your name in ToFind (or ToFound) ;)

This is a remarkable change of tone to previous press releases, I don't see too many differences between comet Borrelly, Wild 2 and Tempel 1. A good thing is that the dirty snowball model can be laid to rest (even the snowy dirtball is out when the dust to ice ratio is in favor of dust), but I'm not sure I agree with the new picture of a comet with less density than a snowbank, possibly without a core????

Then how can we explain all the topological features? How can the features on Wild 2 be explained, I just don't buy all this "fluffiness".

I also wonder on what A'Hearn is basing the idea that the interior is totally different from the surface; did he see any of the subsurface?

And I didn't see any mention of the "bright patches", I'm curious what kind of "fluff' produces those patches.

Cheers.

This is becoming a

antoniseb
2005-Sep-06, 07:50 PM
Then how can we explain all the topological features? How can the features on Wild 2 be explained, I just don't buy all this "fluffiness".

It is interesting that the craters on Wild 2 are not thought by this team to be impact craters...

This second article (overview of conclusions, not detailed observations yet) DID say that there was spectral evidence for subsurface water in the impact.

They haven't said anything about how they have come to the conclusion about the density, but the only way they could be sure would be if they were able to measure accurately the gravitational influence of the comet nucleus on the spacecraft (impact or flyby).

VanderL
2005-Sep-06, 08:23 PM
Ok, we had a "dirty snowball" model, then a "snowy dirtball" model, is this the start of a "fluffy no-ball" model?


Antoniseb:
This second article (overview of conclusions, not detailed observations yet) DID say that there was spectral evidence for subsurface water in the impact.

There already was evidence of water molecules, there just wasn't any increase (maybe even a decrease) on impact, just a humungous amount of dust; that's why the surface "must be" dusty (or fluffy). It begs the question how jets can form on comets, a large amount of fluff could never account for highly collimated jets, ubiquitous on comets. I wonder what happens to the need for subsurface ice/volatiles, if the "snowball" model is abandoned what can produce the dusty jets?

Cheers.

Jerry
2005-Sep-06, 09:35 PM
Fluffy?? Wasn't it supposed to clang like a bell?? :) :)

(Sorry, I couldn't resist.)

How about a potato covered with dust? Or according to O'Hearn, a potato full of fine dust and crystaline water?

I've missed you guys! and just because I started to sound too much like Hoagland and got myself BANNED, doesn't give you an excuse to take off your THINKING CAPS.

As V- has stated, it is difficult to imagine how a pile of fluffy, snowy dust could form inside an object shape, complete with craters.


The nucleus of Tempel 1 has distinct layers shown in topographic relief ranging from very smooth areas to areas with features that satisfy all the criteria for impact craters, including varying size,

O'Hearn questions whether or not they are craters, because we have not seen craters on other comets. Invalid argument - we haven't looked at any quite this closely. What are they? Eyes? I've seen a lot of potatoes covered with dust, but not one potato filled with finely ground silicates. How would fine dust get inside of anything?????

A better explaination MIGHT be, the probe struck a resilient dusty, icy surface, creating the initial hot water and dust blast. The depressed surface then rebound, bouncing cold icy dust over a fairly broad area of the surface of the comet airbourne.

So I guess, not so much a clang like a bell, but the vibration of a kettle drum.

But like everyone else, I did not predict dust, and the complete absence of Iron from the spectra doesn't help.

O'Hearn needs to release more data that supports his model...As is, I don't buy it.

RGClark
2005-Sep-08, 01:02 AM
Thanks ToSeek,

You better change your name in ToFind (or ToFound) ;)

This is a remarkable change of tone to previous press releases, I don't see too many differences between comet Borrelly, Wild 2 and Tempel 1. A good thing is that the dirty snowball model can be laid to rest (even the snowy dirtball is out when the dust to ice ratio is in favor of dust), but I'm not sure I agree with the new picture of a comet with less density than a snowbank, possibly without a core????
...


The "snowy dirtball" theory specifically means there is more dirt than ice in the comet.


Bob Clark

nutant gene 71
2005-Sep-08, 02:33 AM
Welcome back Jerry!! :)

I once almost got myself "banned" with my multiple-split-personalities (per my disclaimer below), so I understand how it feels to not be, certainly leaves me humbled. I also once thought I had comets figured out, as per this (http://www.bautforum.com/showthread.php?p=449947#post449947),
where I wrote:
This would mean that far ranging comets, those with highly elliptical orbits, would be seen to gather material of dust, water molecules, gases, very far out in the solar system's hypo higher G, and shed that same accumulation on their return trip back into a much lower G domain of the inner solar system. Hence, closer to the Sun they would gas out, or at least drop a few dust balls....but I must admit I'm not sure anymore. If comets are solar system "scrubbers", gathering up dust way out there in the cold of outer system, and releasing dust in the warmer regions close to the Sun, it sort of makes sense to me. But this raises more questions than answers for me, since then comets are not primordial but rather current things. So I really don't know anymore. And the craters on Tempel1, how to explain those, if comet is not that dense? What about Halley's comet? Is it a "fluff ball" too?

Glad you're back!

RafaelAustin
2005-Sep-08, 02:28 PM
Maybe this is a simple question.... I read A'Hearn today say that the comet was maybe "75 to 80% empty space". Doesn't this mess with predicting the trajectory of the comet? I mean, how can the density be 1/5th of what it was originally believed to be? Does that mean it has a really dense core to bring it's total mass up to speed? Or am I just missing something?

Thanks!

VanderL
2005-Sep-08, 02:49 PM
Jerry Jensen:
O'Hearn questions whether or not they are craters, because we have not seen craters on other comets. Invalid argument - we haven't looked at any quite this closely.

I think there might be another reason that A'Hearn doesn't want to see any craters on comets; if they are impact craters, then the formation scenario would have trouble finding a dense enough environment for those impacts to happen. Plus, what would an impact do do a "fluffy no-ball" that is 75-80% empty space?


RafaelAustin:
Maybe this is a simple question.... I read A'Hearn today say that the comet was maybe "75 to 80% empty space". Doesn't this mess with predicting the trajectory of the comet? I mean, how can the density be 1/5th of what it was originally believed to be? Does that mean it has a really dense core to bring it's total mass up to speed? Or am I just missing something?

Maybe it has to do with how this is measured, I'm not sure if the trajectory of the flyby satellite was used, or if other measurements were used, I wouldn't want to guess anything without the data from the Rosetta lander, at least that would give better clues to what a comet is made of.

Cheers.

ToSeek
2005-Sep-08, 03:33 PM
Maybe this is a simple question.... I read A'Hearn today say that the comet was maybe "75 to 80% empty space". Doesn't this mess with predicting the trajectory of the comet? I mean, how can the density be 1/5th of what it was originally believed to be? Does that mean it has a really dense core to bring it's total mass up to speed? Or am I just missing something?

Thanks!

The mass of the comet is so small relative to that of the Sun and the planets that I doubt variations would make much of a difference - for most purposes, its mass is probably treated as zero, anyhow.

VanderL
2005-Sep-08, 03:47 PM
This is what I could find on A'Hearn's density calculation of Tempel 1 (from the Planetary Society weblog)


The trajectories traced out by the ejecta allowed them to measure the force of gravity on the comet directly, and it came out to 50 milligal, or 50 parts in a million of Earth's gravity. That, in turn, lets you back out the mass of the comet, about 7 x 1013 kilograms. That, with the shape model, lets you calculate a density, 0.6 grams per cubic centimeter, but the density has large error bars, about plus or minus 0.35. But if you believe the 0.6 g/cc number, A'Hearn said, "the porosity of Tempel 1 must be at least 75%. The comet's empty."

This should be compared to the orbital and flyby calculations, does anyone know these values?

Cheers.

antoniseb
2005-Sep-08, 03:48 PM
I wouldn't want to guess anything without the data from the Rosetta lander, at least that would give better clues to what a comet is made of.

I agree that Rosetta will tell us a lot more. Future (yet-unplanned) missions will tell us yet more. I think it would be interesting to build another deep-impact type probe to target the next comet coming in with a hyperbolic trajectory (a few percent of all comets seem to come from outside the solar system). Of course next time we'll want a string of flyby cameras, not just the one, and a few more specialized instruments, such as a high speed high resolution camera that can get spectra from the initial flashes.

Jerry
2005-Sep-08, 08:45 PM
This is what I could find on A'Hearn's density calculation of Tempel 1 (from the Planetary Society weblog)...This should be compared to the orbital and flyby calculations, does anyone know these values?

Cheers.

Gravity based soley upon ejecta trajectories ignores (or at best approximates) bouyancy - collision with both gas and fine particulate still propagating from, and in temporary kinetic and triboelectric suspension above the nucleus. It is difficult to explain a density of 0.6g/cc when most of the minerals excavated (or bounced off of the surface) have densities > 2g/cc. If the core is so hollow, why isn't the dust falling into the cracks???

If average particle size is 10microns as advertised, that SHOULD return a bulk density factor of greater than 90% of the solid volume, giving us a density of not less than 1.8g/cc, or 1.4g/cc if the internal nucleus is 50% water - which should also help fill the voids - remember, they found carbonates and other compounds that are only know to form at temperatures > 273K, so the ice making up whatever percentage of the comet was likely at one time, water. Structurally, IAOTO it would take a complex silicate or organic matrix to reduce the density to 0.6g/cc. Any sign of spider webs? There should be cracks, caves and fissures on the surface. There are none. Anyone ever find a geod full of ice and dust?

I don't think that the fly-by would have been close enough to measure a gravimetric perturbation, and the probe was knocked about enough that there would be no hope of recovering a reasonable estimate from the probes acceleration. Orbits are good for estimating the mass of the sun (where Mass sun>>>>Mass Comet and r~1AU), but worthless in estimating the mass of the comet. A reasonable density determination may have to wait for Rosetta. 0.6 g/cc fails too many sanity checks.

VanderL
2005-Sep-09, 10:53 AM
Does anyone have access to the on-line Science articles, the subscription I have does not allow me to see the on-line Deep Impact articles, the publications in Science journal will be "several weeks" later. Please PM me.
Thanks.

VanderL
2005-Sep-09, 11:41 AM
I read the editorial and the abstracts and it seems the message is that the DI mission found sort of what they expected with only one new surprise, the surface shows layering. Everything else is more or less "as expected", or "not too far from what planetary scientists foresaw".

I guess the one thing that distinguishes comets from other celestial objects, their jets and coma, is not worth talking about from the DI point of view. How do these jets form?

Cheers.

Jerry
2005-Sep-09, 02:15 PM
Did they find what they expected, or did they jam what they found into the what-we-expected box? Clays and Carbonates - not part of the standard model. Apparently this was not a big surpise to some, but I can't find any references stating comets would likely contain these types of molecules.

I also remember being taught that comets were not covered with dry dust liek the moon, because of their formation history, low gravity, high moisture content, and frequent 'sweeping' by the solar wind.

A layer of dry dust creates an obvious mechanism for jets: Static electric discharge. Dry silicates with an icy (conductive) interior or underskin: a Leydon jar, charged by continuous interaction with the solar wind. The jets might be localized, where either the dusty layer has been blown off, or is naturally more conductive or geometrically shaped for isolating charges with long lasting periodic capacitive discharges, heating the ice that is released as pressurized water vapor. If this is true, the IR of water vapor very near the comet surface should be quite warm.

Kesh
2005-Sep-09, 02:54 PM
I guess the one thing that distinguishes comets from other celestial objects, their jets and coma, is not worth talking about from the DI point of view. How do these jets form?

Cheers.

Deep Impact wasn't built to study such phenomena. And we've already sent several probes to study the coma. The jets are about the only major features left to investigate closely, and we seem to have a pretty good grasp on how they're formed. Perhaps a future probe will be designed to specifically study them.

VanderL
2005-Sep-09, 03:15 PM
Deep Impact wasn't built to study such phenomena. And we've already sent several probes to study the coma. The jets are about the only major features left to investigate closely, and we seem to have a pretty good grasp on how they're formed. Perhaps a future probe will be designed to specifically study them.

Could you point to those papers where they show their "pretty good grasp"? I have the idea that especially the jets are poorly understood.

Cheers.

Jerry
2005-Sep-09, 04:10 PM
Well modeled? Well understood? As expected? From Wikapedia:


Comets are believed to originate in a cloud (the Oort cloud) at large distances from the sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile materials may come to resemble asteroids..

The obvious implication here is that the water contained in comets has never been unfrozen, therefore, there should not be any clays or carbonates. We should now suspect either: 1) Tempel 1 has a warmer past or 2) The outer solar system contains materials that had a warmer past or 3) Tempel 1 did not form in the outer solar system or 4) amaze your freinds with a new comet theory, because the old one is flawed.


The very darkness of cometary surfaces allows them to absorb the heat necessary to drive their outgassing.

DEAD Wrong! Deep Impact results indicate comets have very low thermal inertia; cooling very quickly: The fine dust on the surface is an excellent insulator, and most of the thermal energy is quickly radiated away.


In 1996, comets were found to emit X-rays [1]. These X-rays surprised researchers, because their emission by comets had not previously been predicted.


It is thought that complex organic compounds are the dark surface material.

Wrong again! Yes? No? Some organics have been spotted, but simple ones.


One theory says that when a comet approaches the inner solar system, radiation from the Sun causes its outer layers of ice to evaporate, but again there is no proof of this.

Well stated, and a sullen contrast with 'we saw what we expected'. The mission was launched because we were not sure what to expect.


In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock.[N] This "dirty snowball" model soon became accepted.



"The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice." However, he goes on to suggest that the ice is proabably hidden below the crust as "either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice".

There is nothing about Tempel 1 that suggests unknown physical processes, no anti matter, no exotic or unknown chemistry, nothing at odds with existing physical theory. But what is known about comets, or at least about this comet is very different from the most widely accepted theoretical expectations, especially with regard to the composition and formational history of the solar system. Stating otherwise demeans the importance of the knowledge gained from the Deep Impact probe.

There is still much to learn.

VanderL
2005-Sep-10, 08:52 AM
There is nothing about Tempel 1 that suggests unknown physical processes

I would love to know what the "bright spots" and "bright patches" are that were visble on comets Wild 2 and Tempel 1 (and possibly on Borrelly too). They seem to be connected to jets (this was shown for comet Wild 2) and there is always a rather dismissive explanation offered; maybe they are reflections, or condensing vapor, but nothing substantial. And they were prominently visible in the last images of the impactor, so spectral data should be available.

Cheers.

Dave Mitsky
2005-Sep-12, 11:30 AM
http://skyandtelescope.com/printable/news/article_1592.asp

Dave Mitsky

antoniseb
2005-Sep-12, 01:53 PM
Thanks Dave, there are some things in this article which I haven't seen before... particularly about the suggestion that all of the comet is made of loose dust.

Jens
2005-Sep-13, 06:31 AM
It's so weird, though. I remember the pictures of the comet, and there are clearly what appear to be craters. If the thing is just loose dust and ice, how would the craters form? I mean, of course there could be craters, but the craters in the pictures appear to be shallow, wide craters like the ones seen on terrestrial planets.

Jerry
2005-Sep-13, 05:37 PM
Exactly! The surface feature betray the dustball model. The clays and carbonates betray the 'primal' material assertion.

The data do not support the conclusions. If I were judging this project at a science fair, the PI's conclusions would rank right down there with the bean sprouts. Put the theory on the shelf, look at the data, and develop a compatible hypothesis.

ToSeek
2005-Sep-20, 05:59 PM
Comet Tempel-1 May Have Formed in Giant Planets Region (http://www.spaceref.com/news/viewpr.html?pid=17842)


Comet Tempel-1 may have been born in the region of the solar system occupied by Uranus and Neptune today, according to one possibility from an analysis of the comet's debris blasted into space by NASA's Deep Impact mission. If correct, the observation supports a wild scenario for the solar system's youth, where the planets Uranus and Neptune may have traded places and scattered comets to deep space.

VanderL
2005-Sep-20, 06:42 PM
Comet Tempel-1 May Have Formed in Giant Planets Region (http://www.spaceref.com/news/viewpr.html?pid=17842)



Quote:
Comet Tempel-1 may have been born in the region of the solar system occupied by Uranus and Neptune today, according to one possibility from an analysis of the comet's debris blasted into space by NASA's Deep Impact mission. If correct, the observation supports a wild scenario for the solar system's youth, where the planets Uranus and Neptune may have traded places and scattered comets to deep space.

Impressive, as I said elsewhere, we seem to know a lot more about where comets were formed and what happened to planets like Neptune and Uranus that about the mechanism that produces a comet's jets.

Cheers.

Jerry
2005-Sep-22, 03:47 AM
If the model for the solar system is not working, shuffling a couple of planets around is not the right approach. This is a silly attempt to save a failing model.

As more and more data arrives from Cassini, the physical properties and molecular structure of Saturn's moons will require more and more revisions.

Rocks.

Manchurian Taikonaut
2005-Sep-22, 09:05 PM
http://skyandtelescope.com/printable/news/article_1592.asp

Dave Mitsky


great info :)

Jerry
2005-Sep-23, 01:46 AM
great info :)


"Geologists are convinced that there is nothing on [Tempel 1] that suggests these are not craters," says Deep Impact science team leader Michael A'Hearn

and in the same article:


The impact physics revealed that the comet is held together only by self-gravity rather than by structural bonds between the cometary particles themselves.

The only reasonable self-gravitating shape a rotating pile of dust opposing the solar wind should form is a sphere, or something close to it. Temple I has the aspect ratio of a potato.

Can someone, anyone, explain this to me as part of any reasoning process?

Without structural bonding, how does one form a crater? I have never seen a crater rim in a sand dune, or an ocean. Even if they are not craters they are clearly delineated surface features. Transparent tape?

Superluminal
2005-Sep-24, 01:49 AM
It seems that potato, or some variant, is the preffered shape of most asteroids and comets that have imaged close up. It would be my guess, that any object under a certain mass or diameter, won't have the gravity to assume a sperical shape.

Jerry
2005-Sep-24, 05:09 PM
According to the article, the comet is made of dust, and gravity is the only force holding the nucleus together. If this is true, over the millennia the nucleus has existed, the shape should conform to a 'least energy' model: Whenever disturbed, the dust should resettle in to lower and lower gravimetric wells. I can see some potential for dune-like arrangements, due to the solar wind, but not craters and scarps. The model is SERIOUSLY flawed.


I would love to know what the "bright spots" and "bright patches" are that were visble on comets Wild 2 and Tempel 1 (and possibly on Borrelly too). They seem to be connected to jets (this was shown for comet Wild 2) and there is always a rather dismissive explanation offered; maybe they are reflections, or condensing vapor, but nothing substantial. And they were prominently visible in the last images of the impactor, so spectral data should be available.


I don't understand why there is so much reluctance to discuss these features - are they significant or not? Why or why not? Ignoring them in the scientific articles reporting deep impact results does not make them go away.

I can't see any evidence from what has been reported that the comet was deeply excavated, especially if the impact angle was 20 degrees. A slight revectoring of the energy - A surface trough, slope, hump or resiliency - and
instead of excavating a deep crater, the glacing blow would raise a lot of surface dust. IAOTO this is the simpliest explanation for the observational data that has been presented, and even more compatible with most a prior models, sans dust.

Superluminal
2005-Sep-24, 05:25 PM
There are two craters, near the impact sight, that appear to have raised rims consistant with impact formation. Most of the other craters visible, look like sink holes.

IIRC, the white patches, are believed to be either exposed ice or deposits for jet activity.

antoniseb
2005-Sep-24, 05:41 PM
I can see some potential for dune-like arrangements, due to the solar wind, but not craters and scarps. The model is SERIOUSLY flawed.

Hi Jerry, just because you can envision solar-wind-based dunes (I can't BTW) doesn't mean that the model is seriously flawed. It only means that you disagree with the model. Tell us, please, how you think that the solar wind could cause dunes big enough to be see in the Deep Impact images? How much energy do you think solar wind could impart to a piece of Comet Dust? Enough to get it to roll over? I doubt it.

VanderL
2005-Sep-24, 07:41 PM
There are two craters, near the impact sight, that appear to have raised rims consistant with impact formation. Most of the other craters visible, look like sink holes.

IIRC, the white patches, are believed to be either exposed ice or deposits for jet activity.

Hi Superluminal,

One thing from the comet close-ups is clear, these bright patches are ubiquitous and from the Wild 2 mission they were correlated to jets; from the abstract (my bold):


We interpret the nucleus properties and jet activity from the Stardust spacecraft imaging and the onboard dust monitoring system data. Triangulation of 20 jets shows that 2 emanate from the nucleus dark side and 16 emanate from sources that are on slopes where the Sun's elevation is greater than predicted from the fitted triaxial ellipsoid. Seven sources, including five in the Mayo depression, coincide with relatively bright surface spots.

Several things are important here; jets emenate also from the dark side of a comet (excluding direct surface irradiation as jet mechanism), they correlate to the bright spots and this was a year ago. Why would the Deep Impact team not be looking at the bright patches that were extremely visible in the images. What is the importance of the placement of the patches/spots in relation to surface features. This image (http://stardust.jpl.nasa.gov/highres/1097899fig7_s.jpg) shows that this bright spot on Wild 2 seem to hover above the surface, just like the spots/patches on Tempel 1. Apparently the spots are the origins of the jets and nobody seems interested in finding out more about these features? A'Hearn talks about "reflecting surfaces" and doesn't even acknowledge their significance; isn't he aware of the Sekanina publication?
Apparently, if it doesn't fit the model, silence is the only answer.

Cheers.

Cheers.

Superluminal
2005-Sep-24, 08:07 PM
Hi VanderL. I don't remember seeing any white patch that appeared to hover over Temple 1. Most of the patches seem to be associated with fissures, judging from their alignments. So I agree with them that they maybe deposits from jets.

From what I understand, they are still examining the best computer enhanced hi-res images. I hope they release them pretty soon.

VanderL
2005-Sep-24, 09:53 PM
Hi VanderL. I don't remember seeing any white patch that appeared to hover over Temple 1. Most of the patches seem to be associated with fissures, judging from their alignments. So I agree with them that they maybe deposits from jets.

From what I understand, they are still examining the best computer enhanced hi-res images. I hope they release them pretty soon.

They certainly seem to hover over Wild 2 and while the images were a bit blurry from Tempel 1 there are some spots situated conspicuously over cliff walls, seemingly unattached to the surface. This image (http://www.thunderbolts.info/tpod/2005/images05/050708smoking.jpg) shows some details (is it possible to get an image in a post?), the bright spots tend to "follow" the feature A'Hearn described as a scarp, in general they tend to be near the "high points". Also in this composite image one of the craters has a sinuous channel at it's rim, normally these are explained by lava flows, which is impossible to fit into the fluffy picture painted by the DI team.

Cheers.

Jerry
2005-Sep-25, 04:57 AM
There are two craters, near the impact sight, that appear to have raised rims consistant with impact formation. Most of the other craters visible, look like sink holes.

Like sink holes, or craters filled with dust?


IIRC, the white patches, are believed to be either exposed ice or deposits for jet activity.

,,,On Wild 2, the jet activity did not seem to be coordinated with solar intensity - jets bursting from the opposite side. If Wild 2 has a surface with as low of thermal inertia as Tempel 1, what is triggering them?


Hi Jerry, just because you can envision solar-wind-based dunes (I can't BTW) doesn't mean that the model is seriously flawed. It only means that you disagree with the model. Tell us, please, how you think that the solar wind could cause dunes big enough to be see in the Deep Impact images? How much energy do you think solar wind could impart to a piece of Comet Dust? Enough to get it to roll over? I doubt it.
No, I would only expect the smallest of ripples from the solar wind, if at all - that is the problem: Dustballs shouldn't have surface features.

Superluminal
2005-Sep-25, 02:43 PM
What was the rotation rate of Wild2? I wouldn't expect a jet to just shut down instantly at local sunset. If there are alot of volitales deep inside Wild 2, a jet could keep erupting after local sunset.

VanderL
2005-Sep-25, 03:56 PM
What was the rotation rate of Wild2? I wouldn't expect a jet to just shut down instantly at local sunset. If there are alot of volitales deep inside Wild 2, a jet could keep erupting after local sunset.

The rotation rate is unknown for comet Wild 2, would you believe it (Tempel 1's rotation rate is 2 days), at any rate, if it's slow it would give solar radiation a chance to heat the surface, but it would pose serious problems for the "night side" jets. If it is faster, it would mean less heating, so it seems solar heating is not a viable way to produce jets. Add to this the finding from the infrared data of Tempel 1 that heat is dissipated almost immediately, and it is very likely that solar heating is not causing the jets.

Cheers.

Jerry
2005-Sep-27, 04:45 AM
The rotation rate is unknown for comet Wild 2, would you believe it (Tempel 1's rotation rate is 2 days), at any rate, if it's slow it would give solar radiation a chance to heat the surface, but it would pose serious problems for the "night side" jets.

...If the Deep Impact derived "Old Twinkie" (dry dust filled) model is correct, where is the moisture, period?

This comet has me absolutely vexed, both in terms of A'Hearn's puzzling conclusions about the structure, and in terms of what would be a reasonable alternative. The lack of orientation between solar heating and jets, and the lack of thermal conductivity in the comet surface make a static electric discharge of some kind, either triggered by the solar wind, or some other electromagnetic field effect; seems to me to be the most likely remaining options.

ToSeek
2005-Oct-03, 04:53 PM
Sunshine on Comets: Part I (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1731&mode=thread&order=0&thold=0)


Jessica Sunshine is the Deep Impact mission scientist responsible for the onboard infrared spectrometer. In the first half of this two-part interview, she discusses what the comet's nucleus looked like before and after impact, and explains why it's so difficult to piece together the spectroscopic data.

Jerry
2005-Oct-03, 06:19 PM
JS: What's really exciting is it's not just more, it literally became glowing. If you were in a darkened room, the hot gases would've lit up the room. The vapor cloud was just phenomenal - it saturated some of our pixels. But the cloud also was moving very quickly, because by the next integration it was gone.

AM: How long is an integration?

JS: 720 milliseconds...
Very candid, and very interesting. The higher the temperature and the shorter the temperature burst upon impact, the harder the surface. This very hot burst, limited to less than 720 milliseconds, seems to me to indicate a billard ball-like resilience, not a thin candy shell.


The cometary crater left behind as simulated in digital rendering prior to the July 4th encounter.
This is bad. Why is a prior-to-impact simulation featured in a post-impact article? Where are the post-impact images for comparison? The implication is that this is what the crater looked like, while it almost certainly did not: A radius this wide should have been visible, some of the 'cracks' deconvolutable, in the post impact images.

ToSeek
2005-Oct-06, 04:35 PM
Sunshine on Comets: Part 2 (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1734&mode=thread&order=0&thold=0)


Jessica Sunshine is the Deep Impact mission scientist responsible for the onboard infrared spectrometer. In the second half of this two-part interview, she discusses whether Deep Impact has altered our ideas of how comets are formed and how important they've been in Earth's history.

ToSeek
2005-Oct-14, 04:47 PM
Comets Seem to Be Icy Dirtballs (http://www.universetoday.com/am/publish/comets_icy_dirtballs.html)


The traditional view of comets is that they're "dirty snowballs"; mostly water ice, covered by a layer of dust picked up as they travel through the Solar System. But after Deep Impact's collision with Comet Tempel 1, scientists are reversing that description: they're more like "icy dirtballs". When Deep Impact smashed into the comet, it released more dust than water vapour. This means that comets are mostly dust and rocks, held together by a water ice "glue".

(Discussion redirected from UT Stories area)

VanderL
2005-Oct-14, 05:21 PM
Comets Seem to Be Icy Dirtballs (http://www.universetoday.com/am/publish/comets_icy_dirtballs.html)
(Discussion redirected from UT Stories area)

That's the latest description of a comet that needs to contain ice(s) and volatiles to explain jet formation. Whipple's snowball model has slowly evolved into a dustball, but not because we didn't have enough data, but because we haven't come up with a different jet mechanism. There is not enough ice or volatiles or sunlight (Wild 2 had jets on the dark side), and since the Deep Impact findings, there is also no way that any solar energy can reach the supposed ices and volatiles below a dust layer.

So what comes after the dustball? I hope we don't have to wait for the Rosetta mission to see the logical conclusion of the shift from snow to dust to rock.

Cheers.

Wolverine
2005-Oct-15, 12:13 AM
I'd stress patience here. By January a wealth of additional data from Deep Impact will be available. While Tempel 1 and Wild 2 share a number of properties, their surface morphologies are quite different. It takes time to process all the details -- I wouldn't be overly eager to discard the modeling before the results are in.

Joeblake
2005-Oct-15, 01:56 AM
>> The model is SERIOUSLY flawed.

Indeed it is....... why has global and legal implications.

Wolverine
2005-Oct-15, 02:02 AM
>> The model is SERIOUSLY flawed.

Indeed it is....... why has global and legal implications.

Global and legal implications? What exactly do you mean? This (http://www.bautforum.com/showthread.php?t=17709)?

Superluminal
2005-Oct-15, 02:03 AM
I think that as we study differant comets up close in the future, we will discover that comets are like snow flakes. Many similarities, but each one will be unique in it's own way.

One comet may fit the dirty snowball model.

The next may fit the icy dirtball model.

The third may fit something we havn't thought off yet.

Joeblake
2005-Oct-15, 02:14 AM
>> This comet has me absolutely vexed, both in terms of A'Hearn's puzzling conclusions about the structure, and in terms of what would be a reasonable alternative. >>

JJ, your concern is warranted.... I would direct you to the chemistry of hydrogen and oxygen in a rarefied environment.


But what concerns me more is

(A) What was the velocity change measured once Tempel 1 "settled down" (about two weeks after impact)

(B) What energy balance was calculated... ie total energy output - impact energy

(C) What is the comet's new trajectory in 3D space


>> Many compounds were seen in the spectra, including water, carbon dioxide, hydrogen cyanide, methyl cyanide, and other organic molecules. >>>
http://skyandtelescope.com/printable/news/article_1592.asp

Since water can only be detected as the hydroxyl ion, what is markedly absent from the spectral analysis is oxygen and hydrogen components.

and how water ice (when hit by a mosquito) can liberate << In total, the collision ejected about 10 million kilograms (11,000 tons) of material from the surface.>>>, is beyond comprehension.


not believable science, so what's up ?

Superluminal
2005-Oct-15, 02:27 AM
When the mosquito is traveling 6 miles per second and impacts a body with a powdery surface and a gravitational field weak enough that you could jump into orbit, not surprising that alot of material was liberated.

Wolverine
2005-Oct-15, 02:28 AM
Joeblake was a new incarnation of the previously banned Zarkov.

http://www.bautforum.com/images/icons/icon4.gif Be warned: If you are banned and try to get back in by spoofing or changing your email, appropriate action will be taken -- not limited to but including contacting your ISP.

VanderL
2005-Oct-15, 11:27 AM
Joeblake was a new incarnation of the previously banned Zarkov.

http://www.bautforum.com/images/icons/icon4.gif Be warned: If you are banned and try to get back in by spoofing or changing your email, appropriate action will be taken -- not limited to but including contacting your ISP.

What? You can throw someone from the internet?

Fraser
2005-Oct-15, 01:23 PM
Wolverine said "contacting". Essentially we can try and confirm through the ISP that someone has created a sock puppet. Some ISPs may consider this kind of action a violation of the user's service agreement.

genebujold
2005-Oct-16, 01:59 AM
Unfortunately, the practice of banning via IP address is a very popular, but damaging practice, as many Internet denizens in other countries reside behind their ISP's high-powered NATs to save IP address costs, and as a result, banning the "user's" IP address often bans thousands of innocents.

Furthermore, contacting their ISPs is an often futile process.

The best thing to do is simply ban them from the board and if they begin posting junk again, ban 'em again. Use the IP address to help ID them, but don't ban the IP address itself, and realize that many (even thousands) of users may share the same IP address.

It's more work, true. But after a while they get tired and go elsewhere, and you haven't slammed thousands of innocent users in the process.

If you don't understand the difference between a NAT, a proxy, a sock pupput, and a firewall, then you've really no business banning anyone by their IP address!

This, for example, is a sock puppet: http://en.wikipedia.org/wiki/Sock_puppet

Ok... This is: http://en.wikipedia.org/wiki/Internet_sock_puppet

Thus, the creation of a sock puppet is a matter that rests entirely within the scope of whatever board on which the user is registered, and is of little concern (if any) of the ISP's.

Using NAT, on the other hand, to hide more than one user behind a single-user-only account is definately a violation of an ISP's policies. My ISP allows it, provided all computers are located within the residence and are owned and used by my family.

Using a proxy may or may not be a violation, depending upon what that proxy does (the functions which are many, and varied).

Finally, perhaps the best-understood term is the firewall, which is almost invariably used to keep out the bad guys.

And there's absolutely nothing wrong with that!

George
2005-Oct-17, 03:12 PM
Please help this novice understand the implactions of a dustier snowball.

Speculating on how a comet of the Jovain realm could have more dust, wouldn't countless minor vaporizing impacts, in it's early days, free the lighter elements to be sailed away by our youthful sun's strong winds? Thus, reaccretion would be from higher concentrations of dust. Is this possible?

Jerry
2005-Oct-17, 05:38 PM
I think Wolverine is correct here - let's hope firmer groundwork when the full science data is released.

It is not too soon, though, to speculated that this comet poses vexing constraints upon the standard model. The dust and low moisture are suprises, but not necessarily problems. Thermal inertia - the capacity of Tempel I to capture and hold radiation from the sun, is a big issue.

The Deep Impact 'mother ship' measured how fast this very black object lost heat as the comet rotated away from the sun, and the answer is 'very fast'. This makes it difficult to conjure up heat transfer mechanisms necessary to create the vapor jets observed on the dark side of Wild 2, or vapor jets period from Tempel 1.

The observations of Iron compounds and carbonates further complicates the story: Either the 'primal' material used to formulate the solar system is more varied in composition than the standard model suggests, or this comet is not primal. All the fine dust suggests this comet is a solar dust mop.

George
2005-Oct-17, 06:51 PM
The observations of Iron compounds and carbonates further complicates the story: Either the 'primal' material used to formulate the solar system is more varied in composition than the standard model suggests, or this comet is not primal. All the fine dust suggests this comet is a solar dust mop.
Thanks for the basic approach.

Is there a transition zone for comets/asteroids; where the object is more of a blend of the two?

Superluminal
2005-Oct-19, 01:09 AM
As I said in an earlier post: I believer that there are going to be nearly as many differant kinds of comets as there are comets themselfs. Wild 2 may be composed of totally differant proportians of ice, and dust than Temple.

George
2005-Oct-19, 04:08 PM
Composition variations makes sense. However, I don't know that my transition zone idea does, especially if the transition zone was near Jupiter.

Superluminal
2005-Oct-22, 11:32 PM
I was just reviewing the impact movie located at:
http://www.nasa.gov/mov/121520main_HRI-Movie.mov

On the right side of the image, inside the large crater, the one with the white streak in it. After watching it several times, it seems as if there may be a very faint jet erupting just after the impact. Maybe someone with a better monitor or eyes than I have, can look at it and tell us what they think?

Jerry
2005-Oct-23, 04:24 PM
Sorry - I can't find a player for this clip.

Wolverine
2005-Oct-24, 12:27 PM
You could use QuickTime (http://www.apple.com/quicktime/download) or QuickTime Alternative (http://www.free-codecs.com/download/QuickTime_Alternative.htm).

George
2005-Oct-24, 01:45 PM
Didn't I read there was a jet seen just prior to impact?

VanderL
2005-Oct-25, 07:34 PM
I think Wolverine is correct here - let's hope firmer groundwork when the full science data is released.

It is not too soon, though, to speculated that this comet poses vexing constraints upon the standard model. The dust and low moisture are suprises, but not necessarily problems. Thermal inertia - the capacity of Tempel I to capture and hold radiation from the sun, is a big issue.

The Deep Impact 'mother ship' measured how fast this very black object lost heat as the comet rotated away from the sun, and the answer is 'very fast'. This makes it difficult to conjure up heat transfer mechanisms necessary to create the vapor jets observed on the dark side of Wild 2, or vapor jets period from Tempel 1.

The observations of Iron compounds and carbonates further complicates the story: Either the 'primal' material used to formulate the solar system is more varied in composition than the standard model suggests, or this comet is not primal. All the fine dust suggests this comet is a solar dust mop.


http://www.spaceref.com/news/viewpr.html?pid=18095
This article is what Jerry was referring to, the heat inertia is low, meaning the heat from the Sun is gone when the comet surface turns into shadow. If this comet's heat inertia is anywhere near comet Wild 2's heat inertia it totally invalidates any model of jet production based on solar heating. On Wild 2 specifically, jets were emitting from the dark side and if we get any news on the jets from Tempel 1 I suspect it will confirm this impossibility.

To show what I mean: this website shows results from all the telescopes that imaged the impact.
http://deepimpact.umd.edu/collab_pub/imagep.shtml

Click on "Images" and look at the result from the NOT telescope in Spain:
Image caption:

Comet jets
The images were taken with the 2.5m NOT telescope at El Roque de los Muchachos observatory (La Palma, Spain). The first image was taken about 9h before impact, the second image about 15 hours after impact. They were both enhanced (Laplacian filter) to highlight structures in the coma. New jets (in black) appeared after the impact, the two jets observed in the previous night are still active. Also the curved expanding impact dust shell (in white) is visible at ~18 arcsec (corresponding to about 12,000km) from the comet nucleus.

I'm not sure which side of the comet is turned towards the Sun, but it seems the right side (after impact) shows a "shell" presumably lit by the Sun. If the Sun lights the comet from the right, it would be interesting to see from which specific points of the comet's surface the jets emanate. It needs triangulation, I hope it will be published soon. Another thing that strikes me as odd is the absence of any mention of the "bright patches" (in the recent Science articles) and the insistence of the team that no new jets were formed. The image above clearly shows otherwise, the existing jets remained, and new (short-lived) jets emerged. My guess is that the findings don't "fit the bill", and common practice is leave out the difficult issues whenever possible.

Cheers.

01101001
2005-Dec-02, 09:55 PM
Just a Deep Impact update:

NASA - Mission Update - November 2005 (http://www.nasa.gov/mission_pages/deepimpact/media/deepimpactf-20051128.html)


In the past month, the science team has continued with its data analysis. Many people don't realize the detailed computations that are required to convert a picture made up of raw data numbers returned from space into an image containing numbers of physical meaning.
[...]
Another effort that has taken significant time has been processing images to find evidence of the crater formed by the impact. Our experts in deconvolution and image processing have taken on the task of image enhancement to find the crater. It is apparent that the crater cannot be seen with certainty through all the dust that was ejected from the impact. We measure the width of the shadow cast by the ejecta plume to set a maximum value for the crater diameter. The crater cannot be larger than the width of the shadow cast.

VanderL
2005-Dec-03, 12:37 AM
Thanks for the link,

I'll try to find what I'm looking for (what causes cometary jets, and what are the bright spots/patches seen in close-ups of comets), but I'm not very hopeful.


Cheers.

VanderL
2005-Dec-04, 03:07 PM
Just a Deep Impact update:

NASA - Mission Update - November 2005 (http://www.nasa.gov/mission_pages/deepimpact/media/deepimpactf-20051128.html)

I may be mistaken, but there is absolutely no news in this update, merely some whining that it is hard work to measure the size of the crater (duh, you can't measure the crater size until the dust settles and not with a comet in between!). Where are all the results of the triangulation measurements of the jets, the acknowledgement for the lack of water and explanation for the bright patches and the "double flash"? I guess the team has, after almost 6 months' work, only released the data that fit the preconceptions (ice and volatiles) and refuses to speculate on the data that don't fit the now obsolete "snowball" model.

I asked the DI team directly about the origin of the jets and bright spots, several times, but didn't even get an acknowledgement that the question was received.

Cheers.

Jerry
2005-Dec-05, 01:40 AM
There is no question they are downplaying the surprises. These include:

1) virtually all of the ejecta was dust with very little water vapor.

2) The dust is fairly high in iron content. (Remember, comets are thought to consist of only primal material found at the edges of the solar system when it formed. Most of the iron should be in the inner solar system.)

3) The minerals found take significant temperatures ~400+K to form. Again, this was not expected.

While it is true many in the field had been leaning towards an "Icy dirt ball" rather than a "dirty ice ball". the results contraindicate long-standing solar models. If you couple this with the amount of iron showing up on Pheobe, and possibly other saturn moons, the trend is undeniably at odds with the consensus model of solar evolution.

Squink
2005-Dec-05, 04:58 AM
the trend is undeniably at odds with the consensus model of solar evolution.41 days, 6 hours, 14 minutes, 17 seconds til Stardust Return to Earth (http://stardust.jpl.nasa.gov/).

VanderL
2005-Dec-05, 05:24 PM
41 days, 6 hours, 14 minutes, 17 seconds til Stardust Return to Earth (http://stardust.jpl.nasa.gov/).

Only 1224 days, 4 hours, 12 minutes an 2 seconds before the data from the Stardust mission will be released (if it "lands" in one piece).

Btw where are the Genesis data?

Cheers.

01101001
2005-Dec-05, 07:06 PM
Btw where are the Genesis data?

According to the timeline (http://genesismission.jpl.nasa.gov/mission/time/index.html), sample analysis occurs September 2004 through September 2007. I don't know if that's been updated to accommodate the sample's disheveled state on arrival.

VanderL
2005-Dec-05, 09:58 PM
According to the timeline (http://genesismission.jpl.nasa.gov/mission/time/index.html), sample analysis occurs September 2004 through September 2007. I don't know if that's been updated to accommodate the sample's disheveled state on arrival.

Nothing about progress reports, or news releases? I can't imagine any project that takes 3 years of sample analysis and releases it's data all at once, surely not every analysis takes this long?

Cheers.

Superheat
2005-Dec-07, 03:43 PM
Hello everyone. I'm new, just tooling around and found my way here.

In case you're interested, Dr. Schultz is here at the Ames Vertical Gun Range this week conducting some experiments related to Deep Impact. I cannot go into too many specifics (he keeps these things tightly to himself until numbers are crunched and such), but I can answer general questions.

As for me, I am an engineering tech here at NASA Ames, and have been one of the three operators of this and other light gas guns for the past 5+ years.

Just thought I'd say hello and see if I could provide some insight into the research related to this event.

VanderL
2005-Dec-07, 10:48 PM
Hello everyone. I'm new, just tooling around and found my way here.

In case you're interested, Dr. Schultz is here at the Ames Vertical Gun Range this week conducting some experiments related to Deep Impact. I cannot go into too many specifics (he keeps these things tightly to himself until numbers are crunched and such), but I can answer general questions.

As for me, I am an engineering tech here at NASA Ames, and have been one of the three operators of this and other light gas guns for the past 5+ years.

Just thought I'd say hello and see if I could provide some insight into the research related to this event.


Hi Superheat,

Welcome to the forum, I hope you can give some extra dimension to this Deep Impact thread, there's many questions and I hope you stick around to answer a few.

Here's some for starters: the Deep Impact flyby camera showed an early flash (as Dr Schulz mentioned these were also seen at the Ames facility experiments) showing up in only one frame, meaning it lasted less that 50 mseconds, followed by several frames where "nothing happens" and then the plume starts erupting. How can this time be several frames (at least 100 msec) long? Do you know the specific numbers? At the speed of the impactor such a delay would mean it could have travelled almost a kilometer deep? That seems hardly possible, do you know what could have caused such a delay, maybe the early flash was not produced on impact, but before impact for whatever reason?

Cheers.

George
2005-Dec-07, 11:49 PM
Hello everyone. I'm new, just tooling around and found my way here.

In case you're interested, Dr. Schultz is here at the Ames Vertical Gun Range this week conducting some experiments related to Deep Impact. I cannot go into too many specifics (he keeps these things tightly to himself until numbers are crunched and such), but I can answer general questions.
Welcome. :clap: [My education is m.e.] My general question is...that's a vertically downward gun, right? ;) [I won't ask about pumpkin ballistics.]

Wouldn't penetration, even in talc-like material, require a narrow body? It was Newton who reasoned the displacement material would be accelerated to the speed of the object, roughly; so the cross section to mass ratio must remain small for serious penetration.

Superheat
2005-Dec-08, 06:24 AM
Thanks for the warm welcome!

I'll answer George's question first, and follow up with VanderL when I can get some answers from Pete :-)


Welcome. :clap: [My education is m.e.] My general question is...that's a vertically downward gun, right? ;) [I won't ask about pumpkin ballistics.]

Wouldn't penetration, even in talc-like material, require a narrow body? It was Newton who reasoned the displacement material would be accelerated to the speed of the object, roughly; so the cross section to mass ratio must remain small for serious penetration.

The gun is indeed configured to fire vertically, at angles from 15-90 degress with respect to target materials and gravity. Also, the largest projectile we can safely load into this particular gun is 0.25", and most of the research prior to DI was 0.25" Pyrex, though we are shooting mostly 0.125" projectiles this week. As far as penetration, generally speaking, impacting fine pumice at 6km/sec will yield a crater of approximately 2.5" deep. The bucket we're shooting into is about 6" deep, and the typical projectile is melted away before reaching the bottom.

I hope this is helpful, and I will find out more when I speak to Pete.

Regards.

George
2005-Dec-08, 04:22 PM
As far as penetration, generally speaking, impacting fine pumice at 6km/sec will yield a crater of approximately 2.5" deep. The bucket we're shooting into is about 6" deep, and the typical projectile is melted away before reaching the bottom.
2.5" deep would seem shallow for something at 6km/s (> 13,000mph). However, based on Newton's principle, it doesn't sound so shallow. Since the DI projectile was neither long nor skinny, should'nt we expect it to have very limited penetration?

Superheat
2005-Dec-08, 09:33 PM
2.5" deep would seem shallow for something at 6km/s (> 13,000mph). However, based on Newton's principle, it doesn't sound so shallow. Since the DI projectile was neither long nor skinny, should'nt we expect it to have very limited penetration?

Limited in depth, yes. Fragments of the projectile often penetrate much further, usually close to the bottom and rarely follow a straight trajectory through the material. The amount of excavation can be considerable, but there is a fair amount of relational computation that took place between the experiments here and the actual event. Even after several years of research, I still don't grasp the concept.

Hoping to make up for my lack of cratering physics knowledge, how about a nice picture of Pete profiling a crater in the impact chamber? This was shot by me on 8/20/02 during some early DI research.

Image (http://www.knibbet.com/profile.gif)

George
2005-Dec-08, 09:40 PM
Thanks, Superheat. We like to encourage the use of smaller images. I use Image Shack (http://imageshack.us/) to host large images. You can then insert their thumbnail/link image. This reduces the board's load.

It is nice to see how you profile the crater. This image seems to show a broad crater for the size projectiles you mentioned. Interesting.

Wolverine
2005-Dec-09, 11:52 AM
This was shot by me on 8/20/02 during some early DI research.
Welcome to the forum, Superheat.

I took the liberty of converting your image to a URL for the members here still at the mercy of dial-up. ;)

VanderL
2005-Dec-13, 07:50 PM
Thanks for the warm welcome!

I'll answer George's question first, and follow up with VanderL when I can get some answers from Pete :-)


Apparently you couldn't get any answers from Peter Schulz yet (hope he wants to answer them), in the meantime I have another question: impacting a comet is of course done in hard vacuum, were the experiments at the Ames facility also performed in a vacuum (don't know if it is even possible)? Do you think it matters?

Cheers.

Superheat
2005-Dec-14, 03:25 PM
Yes, the impact chamber here is capable of roughly 100-200 microns, and most of the DI shots were performed at less than 500.

Pete was here until Friday last, and informed me that there are a few disagreements as to the size of the crater and some imaging issues between team members. Most of the info we are looking for here is not anything he wishes to comment on (as usual). I suppose I spoke too soon about forwarding some decent numbers and such, but I honestly thought the answers would be forthcoming. Sorry about that.

In the meantime, I do have info on the guns, in case anyone is interested.


Thanks for your patience!

Jerry
2005-Dec-14, 07:37 PM
Thanks, SuperHeat, for the insight - even no information is better than no clues as to what is going on, and why.

It is healthy that the team members are debating the scenario, and it is reasonable that for a time this is kept in-house.

What would not be healthy, is for Schulz & company to sit on the data unti they all came to a consensus, and announced with no qualifications that such-and-such is how it is.

All the comparative testing can do is constrain the probabilities, perhaps eliminate a few impossibilities. The results of the gun testing will be almost as interesting as the raw data...which we hope will be released at the same time, if not sooner.

01101001
2005-Dec-21, 09:26 AM
I missed this when it happened, and I didn't see it reported here in a quick scan:

AAAS Science, October 14: Special Issue: Deep Impact (http://www.sciencemag.org/content/vol310/issue5746/index.dtl)


Inside Out; Outside In
Summary (http://www.sciencemag.org/cgi/content/summary/310/5746/257)

Research Articles

Deep Impact: Excavating Comet Tempel 1
Deep Impact: Observations from a Worldwide Earth-Based Campaign

Reports

Parent Volatiles in Comet 9P/Tempel 1: Before and After Impact
Subaru Telescope Observations of Deep Impact
The Dust Grains from 9P/Tempel 1 Before and After the Encounter with Deep Impact
Deep Impact Observations by OSIRIS Onboard the Rosetta Spacecraft

Some information from those reports has been incoporated into the Planetary Society Tempel 1 (http://www.planetary.org/explore/topics/asteroids_and_comets/tempel1.html) page.

VanderL
2005-Dec-21, 04:30 PM
I missed this when it happened, and I didn't see it reported here in a quick scan:

AAAS Science, October 14: Special Issue: Deep Impact (http://www.sciencemag.org/content/vol310/issue5746/index.dtl)



Some information from those reports has been incoporated into the Planetary Society Tempel 1 (http://www.planetary.org/explore/topics/asteroids_and_comets/tempel1.html) page.

Thanks 01101001 for the links, what these papers and comments show is a frustratingly shallow summary of tghe Deep Impact data. There were many comments from just after impact claiming all sorts of things, and when I compare them with these findings it is almost as if the mission didn't happen.
No explanation for the very bright flash (too bright to see the impact site), no mention of jets, no mention of the bright patches, no acknowledgement that comets are not "snowballs", nothing about the lack of water detected by several Earth-based observatories, nothing about the "double-flash" phenomenon. In short, to me it is very disappointing, I just hope that more details will follow, but it doesn't look that way at the moment.

Cheers.

ToSeek
2005-Dec-29, 10:37 PM
Deep Impact Mission Update - December 2005: How Do Comets Evolve? (http://www.spaceref.com/news/viewsr.html?pid=19128)


Introduction. - Tempel 1 is like a marshmallow being roasted on a stick. Rotating it takes nearly 41 hours. Each five and a half years it is moved nearer the fire and withdrawn to a cooler place. With each approach to the sun a bit more of its constituent dust and volatile material is driven off into interplanetary space; so it evolves.

VanderL
2005-Dec-29, 11:21 PM
Thanks ToSeek,

It seems the article you link to includes almost nothing from the Deep Impact mission itself; it only repeats what has been "known" before even one probe was sent to any comet. "Comets evolve each time they pass close to the Sun", and that's about it. No mention of how these objects can still form jets after supposedly being "roasted" for billions of years. If the heat is quickly absorbed and dissipated and the comet takes 41 hours to revolve around it's axis (as stated in the article), the "volatiles" won't produce any jets at all, they just "boil off" and form into a layer that shields the comet against solar radiation. It's just another attempt to parade Whipple's "dirty snowball" again, even though we only detected silicates in a very fine dust and almost no increase in water. Sorry for the "rant" the comet story just doesn't hold any water.

Cheers.

Superluminal
2005-Dec-30, 03:32 AM
I'm getting so bored waiting for to release more findings from the missions, that, with great trepidation, I went to Hoaglands sight and read his rantings.

I survived, but just barely.

Jerry
2006-Jan-02, 07:19 PM
I hate like hell to admit it, but Hoaglands assessment of the Deep Impact results is at least as good as the articles by the PI' s (referenced above). Between the fuzzy camera lens (thank you, Ball Aerospace), and all the dust, the science results remain ambiguous.

Three things still stand out:

1) The fine particle size.

2) The lack of moisture in the secondary plume.

3) The detection of iron-rich clays - evidence of material composition similar to the inner solar system, and a 'warm' thermal history.

None of these primary, collaborated, science results were expected. (Based upon the long-standing theory that comets are primal, Kuiper belt objects.)

Superluminal
2006-Jan-02, 08:46 PM
I was surprised that Hoagland ranted more about journalists not caring about the space program, than the fact that Temple 1 is teeming with life, or is a colony ship from Alpha Centari.

RGClark
2006-Jan-04, 01:27 PM
I hate like hell to admit it, but Hoaglands assessment of the Deep Impact results is at least as good as the articles by the PI' s (referenced above). Between the fuzzy camera lens (thank you, Ball Aerospace), and all the dust, the science results remain ambiguous.

Three things still stand out:

1) The fine particle size.

2) The lack of moisture in the secondary plume.

3) The detection of iron-rich clays - evidence of material composition similar to the inner solar system, and a 'warm' thermal history.

None of these primary, collaborated, science results were expected. (Based upon the long-standing theory that comets are primal, Kuiper belt objects.)

Has it been definitively stated there was no water in the secondary plume?
Or no more detected than before the impact?


- Bob

Jerry
2006-Jan-04, 07:19 PM
Has it been definitively stated there was no water in the secondary plume?
Or no more detected than before the impact?


- Bob
http://www.ssc.se/default.asp?division=&groupid=2004517104342856&newsid=200577144355393



From the sequence of spectra it is notable that the signal strength is increased but that the left side of the peak first disappears after the collision and then progressively comes back. At the same time the right-hand side increased continuously. The total amount of water seemed to decrease (area of the peak), oddly enough.

So the actual data indicates that there was little water vapor in the plume, and in fact the dust plume appears to mask the water vapor seen streaming away from us before the probe impacted.

Here are some before and after spectra:

http://www.ssc.se/data/content/IMAGES/200577152950174XXXodinspektra.PDF

However, the article continues:


One explanation could be that the expanding shell of gas hides, i.e. absorbs, the signals from inner molecules heading in our direction. If so, the water outgassing may in fact have increased, as would be expected.

No! No! NO!

There is no reason whatsoever that the distribution of molecules within the dust plume would mask significant water vapor within the plume, that is just plain bogus. DATA should aways trump theory, and expectations based soley on theory should not cause us to discount what we have observed.

Doodler
2006-Jan-04, 07:37 PM
No! No! NO!

There is no reason whatsoever that the distribution of molecules within the dust plume would mask significant water vapor within the plume, that is just plain bogus. DATA should aways trump theory, and expectations based soley on theory should not cause us to discount what we have observed.

If the outer ring of the cratering plume were composed primarily of surface dust shot outward in the initial impact with the water vapor composing the central spire of the ejecta having been stirred up at the direct point of impact.

Its possible, how likely is open to debate, based on what you believe the distribution of material within the comet is. Which makes it all the more unfortunate that the crater won't likely ever be imaged.

Spherical
2006-Jan-04, 09:47 PM
They sound more like tarballs to me. I think the thing is held together chemically rather than gravitationally. If it is as porous as the researchers are saying, why any cratering at all? Shooting a porous material usually results in a clean hole with straight sides. The material needs some brittleness to crater.

Just my opinion.

Jerry
2006-Jan-04, 10:35 PM
They sound more like tarballs to me. I think the thing is held together chemically rather than gravitationally. If it is as porous as the researchers are saying, why any cratering at all? Shooting a porous material usually results in a clean hole with straight sides. The material needs some brittleness to crater.

Just my opinion.
Brittleness, or surface resilience? I guess we are stating the same argument. If Temple 1 has the density they have calculated, it is 90% void.

I just listened to the Planetary Societies' interview with PI Jessica Sunshine. Sunshine said the moisture readings increased by a factor of 10 during the impact, and the 'dust' by a factor of 20. She also said that a periodic jet that should have started just before the impact skipped a cycle. Did it skip a cycle, or was some of the moisture measured during event the the result of the jet, not the impact? The article I quoted above makes it clear the main column of moisture appeared to be 'behind' or shielded by the plume. (Other reports have indicated that the jet would have been on the 'far side' when it erupted.)

The other curious thing is, not once in the ~15 minute interview was it even mentioned that the comet ejecta contained significant amounts of clay - they only mentioned water and organics, which is pretty much what the comet was expected to be made out off before the impact. As I understand it, the ejecta is dominated by silicates and ferro-silicates.

"So is the characterization of a comet as a 'dirty snowball' still intact?"

"Pretty much..."

Spherical
2006-Jan-04, 11:04 PM
Brittleness, or surface resilience? I guess we are stating the same argument. If Temple 1 has the density they have calculated, it is 90% void.

I just listened to the Planetary Societies' interview with PI Jessica Sunshine. Sunshine said the moisture readings increased by a factor of 10 during the impact, and the 'dust' by a factor of 20. She also said that a periodic jet that should have started just before the impact skipped a cycle. Did it skip a cycle, or was some of the moisture measured during event the the result of the jet, not the impact? The article I quoted above makes it clear the main column of moisture appeared to be 'behind' or shielded by the plume. (Other reports have indicated that the jet would have been on the 'far side' when it erupted.)

The other curious thing is, not once in the ~15 minute interview was it even mentioned that the comet ejecta contained significant amounts of clay - they only mentioned water and organics, which is pretty much what the comet was expected to be made out off before the impact. As I understand it, the ejecta is dominated by silicates and ferro-silicates.

"So is the characterization of a comet as a 'dirty snowball' still intact?"

"Pretty much..."


To me, the good news is that there are definitely things like hydrocarbons and ammonia in these wee beasties. Even better, NASA seems inclined to go whack another one. Maybe we'll have better luck with the next set of observations.

Jerry
2006-Jan-06, 08:37 PM
No mention of ammonia in the Sunshine interview, either. Ammonia is a surprising no-show on Titan. I listened to the Planetary Society interview again, just to make sure. Their is no mention of the water / dust increase, only that the 'organic' volume released increased 20 x and water and C02 increased 10 x.

Did I miss something somewhere? Did they decide there was not a release of clays - silicates and pyrenes?

boppa
2006-Jan-07, 05:11 PM
Well modeled? Well understood? As expected? From Wikapedia:

Comets are believed to originate in a cloud (the Oort cloud) at large distances from the sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile materials may come to resemble asteroids.

The obvious implication here is that the water contained in comets has never been unfrozen, therefore, there should not be any clays or carbonates. We should now suspect either: 1) Tempel 1 has a warmer past or 2) The outer solar system contains materials that had a warmer past or 3) Tempel 1 did not form in the outer solar system or 4) amaze your freinds with a new comet theory, because the old one is flawed....


Personally I can not see how you made the gigantic leap from the bit where they originated in a region where they may be solid(etc etc)
add gigantic leap of `logic' here....
to

The obvious implication here is that the water contained in comets has never been unfrozen, therefore,
insert wild guess here

what the???

the ice in my freezer originated in my freezer.
The obvious implication here is that the water contained in my freezer has never been unfrozen, therefore,
all ice originates from my freezer!!

DEAD Wrong!

(i know i know its a strawman-but jeez... simple logic seems to have gone on xmas holidays it seems)
say something like i boppa believe all ice in the universe came from my freezer and uses a torturious path to point back at my previous statement as proof is mildly `unusual' i would have thought..

but its obvious...

and equally obvious is its
DEAD Wrong!

;-)

boppa
2006-Jan-07, 05:27 PM
j.j
im assuming that option 1 in your list isnt one of your prefered options
or are you assuming that temple 1 in particular(and by your quote every comet??) only does a single `death plunge' towards the sun and there dies a fiery death

or possibly you are actually admitting that you find that a comet

Web definitions for comet

(astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit
wordnet.princeton.edu/perl/webwn

may possibly have come in close to the sun and then gone away again-even several times even?

wouldnt this `orbit' thingo consist of a warmer past for this(and indeed most if not all other comets' at times???

Jerry
2006-Jan-09, 04:10 AM
I don't have any strong feeling, theories, what have you, on what a comet should or should not be. I am just bumping my old texts up against the observations. The clays found in Tempel 1 form at relatively high temperatures ~450 k, (or was it C?), These were unexpected.

Also unexpected are the small particle size of the dust.

But what was perhaps most unexpected is the extremely low thermal inertia - the fine particles of blackened sand in a high-void matrix make a great insulated black body, and the nucleus cools immediately when the sun is not shining on it directly. This makes it difficult to explain how the clays formed (therefore, they ARE most likely 'primal'), but it makes it even more difficult to explain what causes the jetting: If no heat is absorbed, why do jets, when they are not facing the sun, jet???

Prior to Tempel 1, it could have been argued that the as they rotisserate, pockets of moisture deep in the nucleus are heated like kernals of popcorn. But if very little solar energy is absorbed, (as the thermal inertia indicates), no popcorn. Very curious.

Spherical
2006-Jan-09, 06:39 AM
It might be a photochemical reaction that is delayed. That's the only thing I can think of anyway.

Doodler
2006-Jan-09, 09:36 PM
Also unexpected are the small particle size of the dust.

I'm curious why you thought this was surprising. It would seem to me that if comets were born in the dust cloud from which the other planets formed, yet had not changed substantially since then, that such a composition would be expected. These bodies are not massive enough to self compress from gravity, so there's no reason to expect the particles composing the comet to condense into more solid form. The coma could then be more easily explained as these fine particles held in suspension around the nucleus through weak ionization charge from interaction with solar wind rather than heat evaporation.

Just a thought, anyway.

VanderL
2006-Jan-09, 11:23 PM
I'm curious why you thought this was surprising. It would seem to me that if comets were born in the dust cloud from which the other planets formed, yet had not changed substantially since then, that such a composition would be expected. These bodies are not massive enough to self compress from gravity, so there's no reason to expect the particles composing the comet to condense into more solid form. The coma could then be more easily explained as these fine particles held in suspension around the nucleus through weak ionization charge from interaction with solar wind rather than heat evaporation.

Just a thought, anyway.

I think you're possibly right in your assumptions, but the major problem I see is that the images of the comets we have seen to date, all imply a very cohesive (if not downright rocky) surface. Craters, steep cliffs and spires are not to be expected when the major constituent is dust. And then again how are the highspeed collimated jets formed (even apart from the question how the heat is supposed to get to the assumed ices/volatiles)? It makes no sense to me whichever way you look at it from the Whipple (dirty snowball, or dusty whatever-ball) point of view.

Cheers.

Doodler
2006-Jan-09, 11:52 PM
I think you're possibly right in your assumptions, but the major problem I see is that the images of the comets we have seen to date, all imply a very cohesive (if not downright rocky) surface. Craters, steep cliffs and spires are not to be expected when the major constituent is dust. And then again how are the highspeed collimated jets formed (even apart from the question how the heat is supposed to get to the assumed ices/volatiles)? It makes no sense to me whichever way you look at it from the Whipple (dirty snowball, or dusty whatever-ball) point of view.

Cheers.

There's enough cohesion in particles of talcum dust to form craters with walls that appear to be more substantial, as if they were solid, when you drop something into a pile of powder. Given that your talking about cubic miles of the stuff in pretty much microgravity, then those whispy features can assume a pretty grand scale, since gravity isn't there to pull them back flatter. Also, its an irregular body, so lacking a consistent shape from which to vary, the "spires" and "valleys" could be nothing more than incidental effects of how the material first clumped together, rather than something that formed later.

As far as the jets, let me partly backtrack myself, there does exist the possibility of compression to more solid form at the point where something impacts upon the nucleus. Over a few billion years, its possible to generate those clumps of ice from whatever liquefication and freezing occurs from impacts to create the sources of the jets (this localized clumping of ices could explain why the locations of some jets are consistent from one close pass to the next).

As far as heat transfer? Beats me, I guess there could be an element of heating as well as ionizing, since the coma might get to be substantial enough for thermal transfer, but I'll leave that to more educated minds than my own.

Jerry
2006-Jan-10, 12:13 AM
I'm curious why you thought this was surprising. It would seem to me that if comets were born in the dust cloud from which the other planets formed, yet had not changed substantially since then, that such a composition would be expected. These bodies are not massive enough to self compress from gravity, so there's no reason to expect the particles composing the comet to condense into more solid form. The coma could then be more easily explained as these fine particles held in suspension around the nucleus through weak ionization charge from interaction with solar wind rather than heat evaporation.

Just a thought, anyway.
Yes, in retrospect, no one should have been surprised by dust, especially since the moon is so dusty, but no one predicted it. I would suppose because in previous close comet encounters (Wild 2, and Halley's), the surfaces looked pock-marked and rocky, not dusty. I'm personally at a loss to try and explain why the jets produce so much moisture, and the impact so little.

Superluminal
2006-Jan-10, 03:49 AM
Perhaps the jets are coming from deeper inside the comet. The DI probe didn't penetrate that far inside.

Doodler
2006-Jan-10, 02:34 PM
Yes, in retrospect, no one should have been surprised by dust, especially since the moon is so dusty, but no one predicted it. I would suppose because in previous close comet encounters (Wild 2, and Halley's), the surfaces looked pock-marked and rocky, not dusty. I'm personally at a loss to try and explain why the jets produce so much moisture, and the impact so little.

I suggested the dustiness partly because of the precident set by Hyabusa and the other American probe that had a close encounter with an asteroid (having a senior moment, so please bear with me), those both reported that the asteroids they encountered were really no more than a conglomeration of boulders and dust that appeared to be completely solid. This in spite of the fact that their appearances clearly looked like your traditionally assumed solid rock, complete with cratering.

Based on where the conversation was going here, I just connected the dots and came up with that possible conclusion.

VanderL
2006-Jan-10, 09:34 PM
There's enough cohesion in particles of talcum dust to form craters with walls that appear to be more substantial, as if they were solid, when you drop something into a pile of powder. Given that your talking about cubic miles of the stuff in pretty much microgravity, then those whispy features can assume a pretty grand scale, since gravity isn't there to pull them back flatter. Also, its an irregular body, so lacking a consistent shape from which to vary, the "spires" and "valleys" could be nothing more than incidental effects of how the material first clumped together, rather than something that formed later.

As far as the jets, let me partly backtrack myself, there does exist the possibility of compression to more solid form at the point where something impacts upon the nucleus. Over a few billion years, its possible to generate those clumps of ice from whatever liquefication and freezing occurs from impacts to create the sources of the jets (this localized clumping of ices could explain why the locations of some jets are consistent from one close pass to the next).

As far as heat transfer? Beats me, I guess there could be an element of heating as well as ionizing, since the coma might get to be substantial enough for thermal transfer, but I'll leave that to more educated minds than my own.


Sorry Doodler,

I have to disagree with your view on the cohesiveness of talcumpowder-sized dust grains, such dust can't take any pressure from inside, and that's where supposedly jets originate. The dust would simply be pushed away and never form the highspeed collimated jets that are observed.

Cheers.

Doodler
2006-Jan-10, 10:04 PM
Sorry Doodler,

I have to disagree with your view on the cohesiveness of talcumpowder-sized dust grains, such dust can't take any pressure from inside, and that's where supposedly jets originate. The dust would simply be pushed away and never form the highspeed collimated jets that are observed.

Cheers.

I understand, take my post for where its coming from, the only Ph.D in my background reads Piled Higher & Deeper. I'm drawing up possibilities taken from a very laymen's stand, so I'm likely off the mark by a bit.

Though let me ask, how much pressure are you assuming those collumated jets create? They may be expansive in size, but are they really creating all that much thrust? If they were, wouldn't their output over time measurably affect the orbit/rotation of the comet? Remember this is a microgravity environment, you don't need to create a lot of pressure hit escape velocity.

Jerry
2006-Jan-12, 06:13 PM
I understand, take my post for where its coming from, the only Ph.D in my background reads Piled Higher & Deeper. I'm drawing up possibilities taken from a very laymen's stand, so I'm likely off the mark by a bit.

In this case, you may be in a better seat for evaluating the results than the PIs. What appears clear to me, is Jessica Sunshine is in denial! The comet revealed a very surprising amount of silicates - clay/dust - including iron containing minerals. But in her interview with the Planetary Society, when she was ask what we learned, she only mentioned and discussed water and organics.

Hearn's public comments have also been along the lines of "the Comet was just what we predicted." I don't see how they can imply this without ignoring the new data.



Though let me ask, how much pressure are you assuming those collumated jets create? They may be expansive in size, but are they really creating all that much thrust? If they were, wouldn't their output over time measurably affect the orbit/rotation of the comet? Remember this is a microgravity environment, you don't need to create a lot of pressure hit escape velocity.
I'm still trying to figure out if they are random or periodic, or something in between. Perhaps on rotations when the 'pointier' side of the nucleus faces the sun, the probability of a static discharge goes up and a lightning-like event occurs that superheats water vapor under the surface. Hey, the energy has to come from somewhere.

VanderL
2006-Jan-12, 07:52 PM
I understand, take my post for where its coming from, the only Ph.D in my background reads Piled Higher & Deeper. I'm drawing up possibilities taken from a very laymen's stand, so I'm likely off the mark by a bit.

Though let me ask, how much pressure are you assuming those collumated jets create? They may be expansive in size, but are they really creating all that much thrust? If they were, wouldn't their output over time measurably affect the orbit/rotation of the comet? Remember this is a microgravity environment, you don't need to create a lot of pressure hit escape velocity.

Doodler, I'm enjoying this discussion, most people are not really interested in exploring possibilities in this way, thanks for that. I'm just as "layman" as you apparently are, I just happen to think the data from the comet space missions don't show any evidence of the Whipple or "dirty snowball" model. What they do show is rather difficult to interpret and it seems the scientists are very reluctant to share the details. The only thing I see is that they try to reconcile the data with the only model they know of.

Okay, to your question.The jets measured at comet Wild 2 are typically 1000 m/s, so that's a very high speed, and the Stardust team measured very short bursts of particles at several hundred kilometers away from the nucleus. The data show hight velocities in narrow "beams" which require (in the snowball model) very high pressure and an extremely narrow "nozzle opening" (a sort of explosive outgassing) for the jets to stay coherent over these distances. In fact so much so, that they proposed that these bursts are generated not on the comet's surface but somewhere in between the comet and the Stardust spacecraft by "fragmentation" to form "swarms". Highly unlikely to me, and an example of fitting the data unto the model.

What I'm curious about is the exact mechanism of how jets are formed, not by modeling, but by producing lab experiments and searching in the images for clues. To me the most important clue is that, at least for comet Wild 2 (and if they release the data maybe also for comet Tempel 1), jets are correlated to the bright spots (Sekanina wrote a paper about it). These brighter areas/patches/spots can be seen in images of comets and we should focus on what they are and not dismiss them as "reflective" areas only 8% less dark then their surroundings. The impact data are even more puzzling, a ball of dust is the last thing I expect comets to be, especially because a comet's orbit and all kinds of interactions with space radiation will quickly disperse any dust. The same way dust is lifted from the Moon, although the stronger gravity there makes sure the dust falls back.
Therefore my guess is that the dust is formed exactly where we see it, at the points where comet jets originate. The mechanism would be independent of solar heating (jets on comet Wild 2 were also active from the "dark side"), but the only way to understand how it works is both close-up imaging and laboratory testing.

Cheers.

Doodler
2006-Jan-13, 03:19 PM
I've been puzzling this in the haze of a cold, and I got to wondering if the jet sources are something like geodes. Ice is introduced to an otherwise dusty object by violent collisions, even though the object itself is but a mass of semicompacted dust, the collision punches into that dustball and compresses a partial shell around it, forcibly introducing water into the dust through flash evaporation. If the dust and water mix acted something like a concrete, which hardened after the impact, that would form a substantial backstop against which the jets could focus their energy outwards over the life of the comet.

Its also possible that the core of the comet is a more solid rock, over which the substantial dust layer accumulated. The likely story is, there's all types of them out there to be found and that there's more than one answer to the question.

As to your belief that the dust should be blown off a comet, I agree, and think that it is in the form of the coma and tail. The longevity of a comet's ability to form a coma and tail I would suppose is a testament to just how much material has accumulated on the comet during its formation 4 billion years ago..

Jerry
2006-Jan-14, 07:49 PM
I try to put the knowledge base into two piles: What we have observed, and what is theory. It is theory that comets formed 4 billion years ago, but it may have been 40 trillion years, and they could be forming now, or any and every number in between.

We know what meteors are like, and asteroid, and it is not a stretch, based upon what we have observed in the last 20 years to guess comets have similar, albiet wetter, compositions.

The geod model is interesting - the center of a small object could certainly be hollowish - with the bulk of the mass at the moment of inertia. If this shell has a metallic composition, it could contain loose dust and water in the interior cavities, and it would not take a great deal of heating of large cavities to create the pressure and jetting we observe. The periodicity could be due to ice clogging the jets as the pressure falls. Once the jet is completely clogged, the pressure rebuilds, and the cycle starts over.

Spherical
2006-Jan-16, 06:00 AM
Yes, in retrospect, no one should have been surprised by dust, especially since the moon is so dusty, but no one predicted it. I would suppose because in previous close comet encounters (Wild 2, and Halley's), the surfaces looked pock-marked and rocky, not dusty. I'm personally at a loss to try and explain why the jets produce so much moisture, and the impact so little.
Arthur C. Clarke warned that the moon might well be covered with a deep sea of dust. Early on, NASA was worried that it could be a very serious problem for landings on the moon.

The jets might well be chemical in origin and the impact purely mechanical.

01101001
2006-Jan-17, 02:57 AM
In this case, you may be in a better seat for evaluating the results than the PIs. What appears clear to me, is Jessica Sunshine is in denial!
By the way, where's your analysis of the data? Are you hiding it from us? It's been more than two weeks since the latest release to PDS:

Deep Impact Project Data Management Plan (http://pdssbn.astro.umd.edu/missions/deepimpact/deep_impact_pdmp.pdf) (PDF 500 kB)


Timeline for DI Project Archiving
Delivery date Archive Products
08/31/2003 Earth based pre-encounter spectra and images.
03/31/2004 Data collected in the 30 days after launch.
03/31/2005 Calibration files and payload tests during Earth flyby.
12/31/2005 Earth based data leading up to impact. Spacecraft measurements through impact.
03/31/2006 Earth based post impact data.
Deep Impact: Mission Results - Data Archiving (http://deepimpact.jpl.nasa.gov/results/archiving.html)

Jerry
2006-Jan-19, 08:29 PM
By the way, where's your analysis of the data? Are you hiding it from us? It's been more than two weeks since the latest release to PDS:

Deep Impact Project Data Management Plan (http://pdssbn.astro.umd.edu/missions/deepimpact/deep_impact_pdmp.pdf) (PDF 500 kB)


Deep Impact: Mission Results - Data Archiving (http://deepimpact.jpl.nasa.gov/results/archiving.html)
I plowed around in there a little bit, and did not find one document newer than May 2005 - The data might be there, but all I turned up was empty folders when I tried to unzip, security notices and the usually network rag about file not found. But I did find this:


There are no proprietary data rights for the DI Mission. Science team members do have a limited amount of exclusive time–not to exceed six months–for validation of data prior to delivery to the PDS.

Fully reduced, calibrated and corrected data products will be produced by the science team for delivery to PDS per the schedule given in Section 6. The PI and Team Leaders are responsible for coordinating all scientific investigations involving the use of calibrated data from their respective instruments and ensuring that all science data products are delivered in a timely fashion.

Similar verbage in the WMAP contracts has not prevented data releases scheduled two years ago to still be in the drawer.

VanderL
2006-Jan-20, 02:29 PM
The PI and Team Leaders are responsible for coordinating all scientific investigations involving the use of calibrated data from their respective instruments and ensuring that all science data products are delivered in a timely fashion.

Jerry,

Just ask for the data, the DI team will coordinate the scientific investigation, so you can co-author the subsequent paper!

Cheers.

Launch window
2006-Jan-23, 05:06 PM
How Do Comets Evolve? (http://www.spaceref.com/news/viewsr.html?pid=19128)

good article !

Doodler
2006-Feb-02, 07:56 PM
A little update for this one.

http://www.space.com/missionlaunches/060202_comet_ice.html

Seems they did find water, and most of it is subsurface.

Jerry
2006-Feb-02, 09:08 PM
Are you and I reading the same article? The article states that Deep Impact found a small patch of Ice on the surface, and that they believe this ice originated inside the nucleus - but there was no data or evidence cited to support this 'belief'.


Tempel 1 has a surface area of roughly 45 square miles, or 1.2 billion square feet. The area taken up by the water ice, however, is only 300,000 square feet. The rest of the comet surface is dust.

0.025% Surface water - this is not the percentage one would normally associate with a dirty ice ball.

“It’s like a seven-acre skating rink of snowy dirt,” said study co-author Peter Schultz of Brown University.

Seven acres of dirty snow found on 45 square miles of dirty dirt. It is time to put Wipple to rest: He was totally wrong.



The same team previously reported that Tempel 1’s interior also contained an abundance of organic material and suggested the comet may have originated in a region of the solar system now occupied by Uranus and Neptune.

I agree with Vander: I see data being mecilessly being pounded upon to force it to comply with prior conceptions. Notice the article mentions only 'organics' in the interior composition, and no clay, no minerals...where did they go?

Look at the July 12th article:


"The major surprise was the opacity of the plume the impactor created and the light it gave off," said Michael A'Hearn of the University of Maryland. "That suggests the dust excavated from the comet's surface was extremely fine, more like talcum powder than beach sand."
...
Deep Impact's collision "woke up" the large dust plume, as well as some gases, including water vapor, carbon dioxide and carbon monoxide. Some hydrocarbons were also detected, according to Schultz.


By September the ratio was changing:


There is more dust than ice, A'Hearn said, but the ratio is less than 10-to-1.

In Jessica Sunshines December interview with the Planetary Society, when ask about surprises, she mentions neither opaque dust, nor the high temperature spike, and talks only about organics and water vapor.

Now look again at this most recent article:


The same team previously reported that Tempel 1’s interior also contained an abundance of organic material and suggested the comet may have originated in a region of the solar system now occupied by Uranus and Neptune.

So "some" hydrocarbons and 0.025% surface ice somehow translates into a ice and organic filling with a dusty clay shell...an M&M glazed with sand?

We banged into a comet and saw a lot of CLAY dust, some organics, and a little water vapor. These are the facts. The rest is just prior beliefs and speculations. I agree, there must be water and organics in the body of a comets somewhere, but dammit, the Deep Impact event provides ZERO evidence that the interior is dominated by water and organics, and ZERO evidence Tempel I once lived where Neptune is. Bad Science!

ToSeek
2006-Feb-02, 11:40 PM
Deep Impact mission reveals comet's icy cargo (http://www.newscientistspace.com/article.ns?id=dn8670&feedId=online-news_rss20)


The consensus model of a comet leading up to the Deep Impact experiment is no longer valid, says Don Yeomans at NASA’s Jet Propulsion Laboratory in Pasadena, California, US, a member of the mission science team. "It's certainly not a dirty iceball or an icy dirtball," he told New Scientist. "It's a very, very weak, dusty structure with interior ices."

Jerry
2006-Feb-03, 03:08 PM
Thank you, ToSeek, That is a much better conclusion, it is based upon Deep Impact data, and I hope he is willing to explain this to O'Hearn and Sunshine, who don't seem to get it.

Even this characterization is troubling: We did not see the impact crater, and the density is based upon an analysis of the hyperbolic return of dust particles to the surface. The error bars on this analysis are at 50%, but I think they could even be wider, since static effects are not know and the initial velocities of the returning particles are inferred. The surface looks like it is cratered, which means there would be surface resilience, strength, a stable morphology.

Finally, to accumulate and hold all of that surface dust implies much greater mass and density - what is holding all that dust? It should escape with each and every impact - just as dust excapes from the moon. This is a very small body.

nutant gene 71
2006-Feb-03, 07:38 PM
Of course, Tempel-1 deep inpact is only a sample of 'one'. But there seems to be enough evidence that perhaps comets are not 'dirty iceballs' anymore, in fact have little water, and are more like dirty 'dust balls' instead.

I've long had a notion (if any had followed my past posts) that comets are little solar region 'vacuum cleaners', gathering molecules and dust on their way out into the colder regions, and letting them loose again into the inner regions of the solar system. At this time, I'm not sure we really know what comet tails are made up of, but they should turn out as de-pressurized dust particles from comets in the hotter inner regions; in the outer colder regions, the process should be opposite, where they gather particles; hence, they don't shrink into nothing over time, but remain replenished. This is not the same as now theorized, that comets are remnants of the early solar system's formation; rather, they are cosmic entities in their own right. Will comets turn into asteroids eventually? Hard to say, but probably not.

BTW, this is perhaps more ATM for now, but as more data comes in from the outer solar system, we should get a better fix on why comets do what they do, and are fluffy dust balls rather than ice balls. (However, for dust to be more attracted on the comet's mass in outer regions might mean something that had been debated on ATM, that G is greater out there than here (http://www.bautforum.com/showthread.php?p=449947&highlight=dust+balls#post449947), but that's a line of reasoning which is not crickey to discuss here.) One way to confirm whether or not comets are distant solar system scrapers is to tally what loose dust and molecules constitute 'empty' space out by the Kuiper belt and beyond.

Omicron Persei 8
2006-Feb-03, 07:38 PM
The surface looks like it is cratered, which means there would be surface resilience, strength, a stable morphology.

That's not necessarily true. A powdery surface can indeed show cratering effect due to a lack of destinctive erosion systems during and after an impact. The dust and ice is ejected and sent on a ballistic trajectory. Those particles with less velocity will, of course, fall back down to the surface...weak gravity or not. Also the initial point of impact could cause a "ripple" of molten material to form due to the powdery surface quickly melting and refreezing...much in the way a crater stiking bedrock can form ripples of molten material inside the blast crater that quickly freeze into place.

Superluminal
2006-Feb-03, 10:50 PM
I don't think that its time to put Whipple to rest. We smacked one comet that has been in the inner solar system for who knows how long. It would have been interesting if we could've smacked a comet that had just come in from the Kuiper Belt. Hale-Bopp or Hyakutake would have been ideal. Unfortunatly comets such as those are rare and don't give us enough lead time to get a mission ready.

Be great if we could get another DI mission ready, and put it on standby for the next great comet.

VanderL
2006-Feb-03, 11:50 PM
I don't think that its time to put Whipple to rest. We smacked one comet that has been in the inner solar system for who knows how long. It would have been interesting if we could've smacked a comet that had just come in from the Kuiper Belt. Hale-Bopp or Hyakutake would have been ideal. Unfortunatly comets such as those are rare and don't give us enough lead time to get a mission ready.

Be great if we could get another DI mission ready, and put it on standby for the next great comet.

I don't agree with you assertion that Whipple's comet model has any value at all. It is clearly shown that there is not enough ice to produce whatever kind of jets (by orders of magnitude). There is now evidence from several comets (Borelly, dry as a bone, Wild 2, with sharp relief and steep cliffs, and now Tempel 1) that show us that ices are a no-show, jets are extremely narrow and can emit from the "darkside". This means that the whole idea of solar irradiation of comets giving rise to outgassing and jet formation is void.

Whipple is out of the picture, the ices have now gone "underground" (subsurface), and please don't tell me you can get the ices heated from the outside through layers of dust. It just doesn't add up. Admit it, we need a new comet model.

Cheers.

VanderL
2006-Feb-03, 11:55 PM
That's not necessarily true. A powdery surface can indeed show cratering effect due to a lack of destinctive erosion systems during and after an impact. The dust and ice is ejected and sent on a ballistic trajectory. Those particles with less velocity will, of course, fall back down to the surface...weak gravity or not. Also the initial point of impact could cause a "ripple" of molten material to form due to the powdery surface quickly melting and refreezing...much in the way a crater stiking bedrock can form ripples of molten material inside the blast crater that quickly freeze into place.

Not so, dust won't give you steep cliffs, it will give you gentle slopes, and what impacts do you think occur on comets? If they are impacted, it will be micro-sized material. Comets are tiny, and don't have any gravity to speak of. They are just not a target for impacts, unless guided by electronics of course
:D .

Cheers.

Omicron Persei 8
2006-Feb-04, 02:03 AM
Not so, dust won't give you steep cliffs, it will give you gentle slopes, and what impacts do you think occur on comets? If they are impacted, it will be micro-sized material. Comets are tiny, and don't have any gravity to speak of. They are just not a target for impacts, unless guided by electronics of course
:D .

Cheers.

Or randomness. Remember how long those comets have been out there. Those impacts probably only happen a billion or so years after its birth...plenty of stuff still floating around the early solar system. Given that these things were cutting in and out of the orbital plain I wouldn't be surprised if they were impacted quite readily with small particles. That would certainly explain its dust coating.

** Edited -- crappy spelling

Jerry
2006-Feb-04, 04:07 AM
Or randomness. Remember how long those comets have been out there. Those impacts probably only happen a billion or so years after its birth...plenty of stuff still floating around the early solar system. Given that these things where cutting in and out of the orbital plain I would be surprised if they were impacted quite readily with small particles. That would certainly explain its dust coating.
Agreed...but I still think the nucleus is more dense than O'Hearn's team. The density is based, in part, upon particle size, and Stardust gives us reason to believe the particle size estimates may be too small. It is EXTREMELY difficult to accurately estimate particles size on the bases of backscattered light.

Remember, the Whipple model was just an educated guess before we had ANY real data. NONE of the real date point in the direction of an icey dirt ball, and certainly not a dirty ice ball.

This is exactly why evidence must be studied objectively, and without preconceptions as to what it means. I had an undergrad professor who insisted on calling the 'Nobel elements', inert gases; even though it was obvious that they react, both naturally and in man-induced synthesis. It was what he had been taught and what he taught for forty years, but it was wrong.

It is ok for a theory that has been taught forever to be wrong - that should be the keystone difference between a scientific theory, and a religious tenent. It has taken NASA six months to admit the Whipple model is now dead. Comets are still very fascinating objects - But Fred would not be defending a dirty iceball with less than 0.01% surface moisture. Fred knew he was mortal, and an educated guess is always trumped by observational evidence to the contrary. The icey dirtball is just as lame. The jets - high in moisture - clearly do not represent the same class of sample ejected by Deep Impact.

Omicron Persei 8
2006-Feb-04, 11:24 AM
I had an undergrad professor who insisted on calling the 'Nobel elements', inert gases; even though it was obvious that they react, both naturally and in man-induced synthesis. It was what he had been taught and what he taught for forty years, but it was wrong.

Hold on inert or "nobel" gases are called so because normal conditions don't allow them to react very readily to other compounds...they have to be forced into doing so; either through a special natural process or a man-made initiation. It wasn't that you were taught wrong, its that inert elements are inert most of the time.


It is ok for a theory that has been taught forever to be wrong - that should be the keystone difference between a scientific theory, and a religious tenent. It has taken NASA six months to admit the Whipple model is now dead. Comets are still very fascinating objects - But Fred would not be defending a dirty iceball with less than 0.01% surface moisture. Fred knew he was mortal, and an educated guess is always trumped by observational evidence to the contrary. The icey dirtball is just as lame. The jets - high in moisture - clearly do not represent the same class of sample ejected by Deep Impact.

So why does a comet have to have a high surface moisture content? Can't voids in a dust covering allow different jets with different compositions depending on the distribution of the compounds within the core? As I see it we <i>are</i> looking at a different class of comet; one that's drier than outer solar system specimens. Whipple may have not been completely correct, but it certainly wasn't wrong. They definately aren't as dry as an asteroid.

VanderL
2006-Feb-04, 04:42 PM
So why does a comet have to have a high surface moisture content? Can't voids in a dust covering allow different jets with different compositions depending on the distribution of the compounds within the core? As I see it we <i>are</i> looking at a different class of comet; one that's drier than outer solar system specimens. Whipple may have not been completely correct, but it certainly wasn't wrong. They definately aren't as dry as an asteroid.

Remember that ice was central to Whipple's model, specifically for the production of jets, the new data show that it doesn't work this way. Whipple's model is wrong, it's that simple (btw Borelly was aslo dry as a bone, so Tempel 1 is not a one-off comet).

Now to get to a new model, whatever the mechanism, I think jets are the key feature to be explained. The "Whipplers" are now resorting to subsurface pockets of ices/volatiles, but that leaves the big question how those pockets get heated to produce jets. I want to point out that jets are produced far from the Sun as well, and remember those jets are very narrow and high speed. Just solar heat isn't going to work.

Cheers.

VanderL
2006-Feb-04, 06:28 PM
Whipple may have not been completely correct, but it certainly wasn't wrong. They definately aren't as dry as an asteroid.

Forgot to mention that asteroids are thought to contain ices too, so your assertion that comets are not as dry as asteroids is unfounded.

As an aside, there is a news item about a binary asteroid (Patroclus) that seems to resemble a comet (based on it's calculated density), so possibly asteroids and comets have much more in common. Since this is the only binary asteroid found to date in the Trojan family of asteroids in Jupiter's orbit, I'm curious what Jerry has to say about this density calculation.

Cheers.

Superluminal
2006-Feb-04, 09:08 PM
All we have looked at are comets that have spent a lot of time in the inner solar system. Even Halleys Comet made numerous passes through the inner solar system. Look at Enceladus, its outgassing as a comet would, but its a moon of Saturn. We would certainly call it a comet if it passed through our realm of space.

Until we can examine comets from the Kuiper Belt or Oort Cloud, I don't think the Whipple model can totally be put to rest. What we found at Temple 1 seems to me to be consistant with an almost burnt out dirty snowball, its mostly dirt now.

Jerry
2006-Feb-05, 12:54 AM
Until we can examine comets from the Kuiper Belt or Oort Cloud, I don't think the Whipple model can totally be put to rest. What we found at Temple 1 seems to me to be consistant with an almost burnt out dirty snowball, its mostly dirt now.

Whipple was trying to characterize the comets we have seen, not what might be out there. Otherwise, I agree - There is no reason that a family of comets cannot exist that more closely resemble the icy moons of Saturn.

Check out this image of a spec of something in Stardusts Aerogel:

http://www.berkeley.edu/news/media/releases/2006/02/01_stardust.shtml

Notice the Sonic coning, caused by the high speed penetration of the particle, and now think about this:

Aerogel has a void volume of >99%. According to NASA, Tempel 1 has a void volume of 90%. Both aerogel and the dust raised from Tempel 1 by Deep Impact are silicates. If Deep Impact entered a body with 90% void volume, most of the energy would be dispersed in the same way it is in aero gel: Outwards, and downward, relative to the point of entry. This is true of fiberglass, kevlar, pumis, steel wool, styrofoam, goose down, wool, and the head on a pint of Guiness. In any subtrate with high void volume, momentum and force are absorbed outward and downward from the point of impact.

Deep Impact's ejecta emerged in the same direction in which the probe impacted. Since there was little water and other volatiles in the ejecta, there should have been very little gas pressure to disipate within the nucleus of the comet. If Tempel 1 has the structure NASA proposes, there should have been little, if any dust emerging from the hole. The model proposed by NASA is STILL fatally flawed.

VanderL
2006-Feb-05, 12:18 PM
All we have looked at are comets that have spent a lot of time in the inner solar system. Even Halleys Comet made numerous passes through the inner solar system. Look at Enceladus, its outgassing as a comet would, but its a moon of Saturn. We would certainly call it a comet if it passed through our realm of space.

Until we can examine comets from the Kuiper Belt or Oort Cloud, I don't think the Whipple model can totally be put to rest. What we found at Temple 1 seems to me to be consistant with an almost burnt out dirty snowball, its mostly dirt now.

Interesting you mention Enceladus, it only makes it worse for the dirty snowball model; if the mechanism responsible for the jets on that moon are comparable with the mechanism that form cometary jets, sunlight is not the source. So, whatever the ice content of the body in question, the results so far, silicates and jets, even from what you describe as a "burnt out dirty snowball", indicate that Whipple's model is wrong on the key points.

We might as well start afresh. Starting with the first important question: how can we get water molecules (or OH-ions) from a surface that contains almost exclusively silicates or dust, without resorting to hidden pockets of ice?

Cheers.

Jerry
2006-Feb-05, 04:40 PM
Upon further reflection, when deep impact slammed into the comet, it is possible to get a reflection from each and every layer - this may be why Sunshine is talking about layering in the nucleus of Temple 1. But layering also requires different strata with different densities. It does not seem likely to me that anything other than a surface layer of dust would produce dust. In other words, the deeper layers should break up in chunks - they must have varying densities to continue to expell ejecta, and the ejecta must vary layer by layer.

We don't see that: We see dust, dust that in my opinion, was much more likely the results of a surface (transitional) wave moving rapidly across the surface of a very hard object.

R.A.F.
2006-Feb-05, 06:59 PM
We see dust, dust that in my opinion, was much more likely the results of a surface (transitional) wave moving rapidly across the surface of a very hard object.

The old "iron covering", right? Clang, clang, clang went the comet, eh?

It would be nice if you could "show us the evidence" instead we get...


The model proposed by NASA is STILL fatally flawed.

...your thinly veiled implication that NASA doesn't know what it is talking about...once again...

I sure would like to know exactly how it benefits NASA to be so "stubbornly" wrong about this...


edited to add...IMO...comets having hard "shells" is an ATM idea...

VanderL
2006-Feb-05, 08:04 PM
Upon further reflection, when deep impact slammed into the comet, it is possible to get a reflection from each and every layer - this may be why Sunshine is talking about layering in the nucleus of Temple 1. But layering also requires different strata with different densities. It does not seem likely to me that anything other than a surface layer of dust would produce dust. In other words, the deeper layers should break up in chunks - they must have varying densities to continue to expell ejecta, and the ejecta must vary layer by layer.

We don't see that: We see dust, dust that in my opinion, was much more likely the results of a surface (transitional) wave moving rapidly across the surface of a very hard object.

The dust is very fine, is it likely that the dust from the impact could support a surface pockmarked with craters, depressions and scarps as seen in the images? Also what about comet Wild 2's surface features, could those be formed in a vast layer of dust?

Cheers.

Jerry
2006-Feb-06, 06:10 AM
The old "iron covering", right? Clang, clang, clang went the comet, eh?

It would be nice if you could "show us the evidence" instead we get...

...your thinly veiled implication that NASA doesn't know what it is talking about...once again...

I sure would like to know exactly how it benefits NASA to be so "stubbornly" wrong about this...

edited to add...IMO...comets having hard "shells" is an ATM idea...
Just Two months ago, Sunshine was still saying comets are 'pretty much what we expected', but two days ago, in this article:

Deep Impact mission reveals comet's icy cargo (http://www.newscientistspace.com/article.ns?id=dn8670&feedId=online-news_rss20)[/QUOTE]

NASA finally stated that Tempel 1 is "Neither a 'dirty ice ball' nor a 'icy dirt ball'" - which is what I have been saying since July 6th", so I feel rather vindicated in my assessment of the observational evidence, which trumps all prior predictions, including mine.

(Incidently, there was a significant amount of iron, as pyroxenes and other mag silicates, in the dust blown off of Tempel 1 by the impact.)

The physics of a copper projectile impacting an object that is 90% void volume will not cause ejecta from the point of penetration, unless there is significant elasicity, or tension in layers near the surface. NASA is telling us this fine dust was ejected from deep in the body of the comet; a conclusion which would require that the dust itself was arranged in compressive, resilient layers, and I don't see how that is possible.

A better model, more consistent with our observations is this: Deep Impact thudded into a rusty, dusty, resilient surface. In the vacuum of space, there is no carrier for a reflective shock wave, and the energy transitioned to a tidal-like surface wave, whipping every gram of dust off the hard surface near the point-of-impact. (I would like to say the surface is composed of Iron and Nickel like many meteors that have impacted the earth, but I can't: The data-in-hand do not support that conclusion.)

Edited to add: I don't see any advantage in the NASA PI's slow acceptance of the implications of the new data. I do think that they so greatly expected the existing model to be verified, that they have been very conservative in the interpretation of the Deep Impact results. I think everyone was surprised; and I don't know anyone who is not puzzled, and having a difficult time coming up with a reasonable answer for how the jets work.

The model I have proposed has nothing to do with new physics of any kind: It is a reasonable, Newtonian interpretation of the data in-hand, which includes pressure wave transmission properties through a solid.

VanderL
2006-Feb-11, 06:29 PM
"When we planned our experiment, we estimated how long it would take for the dust to fall back onto the comet, and multiplied that estimate by 4," said Lucy McFadden, Co-Investigator on Deep Impact. "We only had a limited time to observe because this was all happening at relative speeds of 22,000 miles per hour. To our surprise, the dust never cleared!"

So, what does this little surprise tell us about our knowledge of comets? Does this mean comets have thick layers of very fine dust? This in stark contrast to the visible surface features? Or does it tell us the dust doesn't fall back as expected, or does it tell us something else? I think Jerry has some points about comets that make much more sense than the "mainstream" approach, which consists of either ignoring evidence or fitting the data to an outdated model.

Cheers.

Omicron Persei 8
2006-Feb-12, 03:58 AM
Does this mean comets have thick layers of very fine dust? This in stark contrast to the visible surface features?

What I don't get is why you don't think impacts into powdery surfaces can't make ridges and cliffs. Dry, fine powder allows for steep cratering features. It's the old marble thrown at flour idea. Besides...what is there on the comet, besides outgassing, that'll mess with those features once they've formed. There isn't much erosion going on...

VanderL
2006-Feb-12, 03:01 PM
Does this mean comets have thick layers of very fine dust? This in stark contrast to the visible surface features?

What I don't get is why you don't think impacts into powdery surfaces can't make ridges and cliffs. Dry, fine powder allows for steep cratering features. It's the old marble thrown at flour idea. Besides...what is there on the comet, besides outgassing, that'll mess with those features once they've formed. There isn't much erosion going on...

I can try to explain why I think this very thick dust layer is unlikely:

1. Dust is a good insulator, the heat capacity data are inconsistent with a thick dust layer, the heat disappears as soon as the sunlight is blocked.
2. Dust can move around, so any disturbance will lead to smoothing steep features.
3. Comets, like asteroids and atmosphere-less moons, are bombarded by energetic particles, charging up the particles. This leads to a constant "re-shuffle" of these charges, also leading to smooth surfaces (incidentally this is also thought to be the reason so much dust is on these celestial bodies, as charged dust particles will be attracted).
4. Impacts on asteroids (as described here (http://spacescience.spaceref.com/newhome/headlines/ast16dec98_1.htm)), have been calculated to produce "quakes" also leading to the deposit of dust in the lower parts of the surface.

And I want to add that I'm not the only one questioning that dust can be capable of sustaining the surface features, remember the Nasa team's surprise at the "steep cliffs" and "spires", even overhangs found on comet Wild 2. Furthermore did you actually see the close-up images from comet Tempel 1? There's a lot of scarps and what look like crater rims with almost vertical sides. Dust just doesn't have the consistency to form these shapes. Brownlee commented after the Wild 2 images, that the consistency resembled "freeze-dried ice cream", something that is invalidated by the Tempel 1 observations, no ice only dust.

Cheers.

Omicron Persei 8
2006-Feb-13, 01:03 AM
1. Dust is a good insulator, the heat capacity data are inconsistent with a thick dust layer, the heat disappears as soon as the sunlight is blocked.

Wouldn't that be the case if there WAS a think dust layer? Dust with vacuum occupying the voids would make for a great insulator of surfaces covered with this dust...we know the entire surface isn't covered as such.

2. Dust can move around, so any disturbance will lead to smoothing steep features.

Something has to disturb it. What would that be?

3. Comets, like asteroids and atmosphere-less moons, are bombarded by energetic particles, charging up the particles. This leads to a constant "re-shuffle" of these charges, also leading to smooth surfaces (incidentally this is also thought to be the reason so much dust is on these celestial bodies, as charged dust particles will be attracted).

The inverse square law...live it, know it. The dust would have to be pretty close to be attracted to such an object. And two particles have to have opposite charges even to be attractive. What is the mechanism for this? UV and cosmic rays?

And I want to add that I'm not the only one questioning that dust can be capable of sustaining the surface features, remember the Nasa team's surprise at the "steep cliffs" and "spires", even overhangs found on comet Wild 2. Furthermore did you actually see the close-up images from comet Tempel 1? There's a lot of scarps and what look like crater rims with almost vertical sides. Dust just doesn't have the consistency to form these shapes. Brownlee commented after the Wild 2 images, that the consistency resembled "freeze-dried ice cream", something that is invalidated by the Tempel 1 observations, no ice only dust.

That's why I'm saying that the whole surface isn't covered with a thick layer of dust. Some areas may be thinner in places than others. That dust would be covering the icy core that is responsible for found water traces.

Launch window
2006-Feb-13, 09:07 AM
Deep Impact mission reveals comet's icy cargo (http://www.newscientistspace.com/article.ns?id=dn8670&feedId=online-news_rss20)

great link there !

VanderL
2006-Feb-13, 09:33 PM
1. Dust is a good insulator, the heat capacity data are inconsistent with a thick dust layer, the heat disappears as soon as the sunlight is blocked.

Wouldn't that be the case if there WAS a think dust layer? Dust with vacuum occupying the voids would make for a great insulator of surfaces covered with this dust...we know the entire surface isn't covered as such.

Thanks for this reply, what happens with a dusty layer is that it heats up slowly, and the heat that is eventually captured by the dust layer, will be released slowly, this is not seen. The "uptake" and release is fast. So the evidence is against a thick layer.



2. Dust can move around, so any disturbance will lead to smoothing steep features.

Something has to disturb it. What would that be?

Well, anything from charged particlse through micrometeorites, to larger impacts, and don't forget direct heating and cooling. Also we know comets form jets, they could disturb any existing dust as well.


3. Comets, like asteroids and atmosphere-less moons, are bombarded by energetic particles, charging up the particles. This leads to a constant "re-shuffle" of these charges, also leading to smooth surfaces (incidentally this is also thought to be the reason so much dust is on these celestial bodies, as charged dust particles will be attracted).

The inverse square law...live it, know it. The dust would have to be pretty close to be attracted to such an object. And two particles have to have opposite charges even to be attractive. What is the mechanism for this? UV and cosmic rays?

Yes, anything with enough energy.



And I want to add that I'm not the only one questioning that dust can be capable of sustaining the surface features, remember the Nasa team's surprise at the "steep cliffs" and "spires", even overhangs found on comet Wild 2. Furthermore did you actually see the close-up images from comet Tempel 1? There's a lot of scarps and what look like crater rims with almost vertical sides. Dust just doesn't have the consistency to form these shapes. Brownlee commented after the Wild 2 images, that the consistency resembled "freeze-dried ice cream", something that is invalidated by the Tempel 1 observations, no ice only dust.

That's why I'm saying that the whole surface isn't covered with a thick layer of dust. Some areas may be thinner in places than others. That dust would be covering the icy core that is responsible for found water traces.

Well, that's almost what I'm saying, a little dust, but mostly a solid surface, imo likely a rocky surface. That's why the jetting mechanism is so important. From the data it seems that 2 things can be excluded as jet mechanism:
1. Evaporation of ices; there's not enough to begin with, and there's no increase in volatiles/water from the impact experiment.
2. The data from comet Wild 2 show that the jets are narrow and fast and can be seen ejecting from the dark side of the comet. Inconsistent with any model that supposes solar heating is the energy source (and the fact that comets can't seem to hold on to the heat).

To me this means that comets do not jet because heat from sunlight evaporates pockets of ice/volatiles and are therefore not required to be "dirty snowballs" or "snowy dirtballs" as per Fred Whipple. They can just be some sort of rocky material with an as yet unknown jet mechanism, which at least has something to do with the bright patches/spots (see publication by Sekanina et al. in Science 18JUNE 2004 VOL 304 p1770-1773).

Cheers.

Superluminal
2006-Feb-15, 04:21 AM
But it does seem that sunlight plays a role in jetting. Most comets are more active just after perihelion that when at distance of more than two or three AU's. Although, IIRC, Hale-Bopp was still active after it had receded beyond the orbit of Saturn.

Jerry
2006-Feb-15, 03:44 PM
great link there !
The articles title:

Deep Impact mission reveals comet's icy cargo

Is misleading.


But the mission’s science team says the water ice is present in surprisingly small amounts, covering less than 1% of Comet Tempel 1’s surface.

So a more appropriate headline would be:

"DEEP IMPACT reveals Tempel 1 comet is not a dirty iceball"

It is still unclear where the water vapor came from - was it part of the ejecta, or a background jet? There was a cyclic jet observed in the days before the impact, and if it followed its normal cycle, it would have 'erupted' just before the impact, so if it erupted just after the impact, did water show up in the ejecta, or was it in the background? Or both?

VanderL
2006-Feb-16, 06:17 PM
The articles title:

Deep Impact mission reveals comet's icy cargo

Is misleading.

So a more appropriate headline would be:

"DEEP IMPACT reveals Tempel 1 comet is not a dirty iceball"

To sum it up:

No surface ice, or at least too little by orders of magnitude to explain the coma water abundance.
Dust after the impact, so no (or too little) subsurface ice either.
Surface features are not consistent with a thick layer of fine-grained dust.
Solar heating of any ice/volatiles "pockets" seems out of the question. So, the jet mechanism and the dust production and the water production are all unexplained.

Exit "snowball" model, enter the humbling realisation that we really don't know what makes comets "work".


It is still unclear where the water vapor came from - was it part of the ejecta, or a background jet? There was a cyclic jet observed in the days before the impact, and if it followed its normal cycle, it would have 'erupted' just before the impact, so if it erupted just after the impact, did water show up in the ejecta, or was it in the background? Or both?

We need more details for that, but I would like to remind you of the unexpected observation by the ODIN team (the Swedish telescope) that the water abundance seemed to decrease upon impact.

Cheers.

Jerry
2006-Feb-17, 05:04 PM
This months Planetary Society article on Deep Impact says the Water and organic components decreased by a factor of twenty, however, they calculate the the volume of water actual increased by a factor of 8, but most of the vapor is obscured by the dust. If the amount of vapor increased, but is more abscured, the plume must be totally dominated by the dust component: ((1g/cc)(4g/cc))/(8x20) would tend to indicate that moisture content is no greater than 0.17%, by mass.

The Planetary Society article is disappointing in a couple of respects: There is an artist's depiction of the comet on the first page, and in this image it looks like the nucleus is coated with ice. The caption also calls the comet nucleus a 'dirty snowball', so the mindset is still rather fixed.

Stubborn Lucy, you are. Learning difficult, will be.

Jerry
2006-Feb-20, 04:21 PM
This article:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2192.pdf

Clearly shows that the probe penetrated (thick dust? a cobwebby surface?) in the first three frames, THEN struck a (harder? more resilient) surface that caused it to emit a bright UV flash - but contrary to first reports, this flash was dimmer than expected (!?).

Since it took roughly 125ms before the bright flash occurred, my hypothesis that the dust or surface layer is only 1-3 meters thick is certainly wrong, and even though the angle of impact was 20-40 degrees, the probe must have penetrated quite deeply before the bright flash occurred.

Fascinating structure!

VanderL
2006-Feb-20, 05:30 PM
This article:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2192.pdf

Clearly shows that the probe penetrated (thick dust? a cobwebby surface?) in the first three frames, THEN struck a (harder? more resilient) surface that caused it to emit a bright UV flash - but contrary to first reports, this flash was dimmer than expected (!?).

Since it took roughly 125ms before the bright flash occurred, my hypothesis that the dust or surface layer is only 1-3 meters thick is certainly wrong, and even though the angle of impact was 20-40 degrees, the probe must have penetrated quite deeply before the bright flash occurred.

Fascinating structure!


Ok, so we have to revise the time between the early flash and the second flash to 123 msec. That means the projectile could have travelled another 1254.6 m before the dust plume started to emerge. Or do you think the delay time is consistent with "implosive, excavating and funnelling" action as claimed by the experts?

Cheers.

P.S. The images are unreadable by my computer software, any solutions?

Jerry
2006-Feb-23, 06:13 AM
The experts are saying there is 'layering', which I would assume means that when you get a bright flash after burrowing for 125ms, there was some kind of change in density or resiliency. I can't argue with that. I guess we will never really know.

You are not missing much by not seeing the images, just three very dim spots of light prior to the flash.

01101001
2006-Mar-20, 07:25 AM
Some Lunar and Planetary Science Conference (LPSC) 2006 Deep Impact-talk documents (PDF format):

A DEEP IMPACT MISSION CONTRIBUTION TO THE INTERNAL STRUCTURE OF JUPITER FAMILY COMETARY NUCLEI: THE TALPS OR “LAYERED PILE” MODEL (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1232.pdf)


Based on this proposal, a structural model for the interior, called here the Talps or ‘layered pile’ model, is presented for typical Jupiter family comet nuclei that has an inner core transitioning to an outer mantle consisting of a sequence of thin, randomly stacked, layers, each of limited area and, possibly showing small differences in composition, out to the surface. As presented here this model predicts a correlation between the radial distance and the average thickness of the layers. As long as gravity plays a minor role large nuclei are expected to have thicker surface layers and vice versa.

DEEP IMPACT: THE FIRST SECOND (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1165.pdf)


These frames witnessed the beginning of the conical ejecta plume’s expansion. In addition, they caught the expansion of a cloud of incandescent, probably liquid silicate, droplets that sprayed away from the impact site.

TEMPEL 1: SURFACE PROCESSES AND THE ORIGIN OF SMOOTH TERRAINS (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1364.pdf)


Deep Impact spacecraft [1] obtained high resolution views (better than 10m/pxl) of some 30% of the surface of comet 9P/Tempel 1. The images reveal the nucleus to be a geologically complex body with a) prominent layering, possibly of global extent, b) widespread preservation of apparent impact scars, c) strong evidence of scarp retreat and a diversity of slope morphologies, d) extensive smooth terrains strongly suggestive of flow deposits.

ASYMMETRY OF GASEOUS CO2 AND H2O IN THE INNER COMA OF COMET TEMPEL 1 (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2149.pdf)


The distribution of the gas in the inner coma was mapped and an asymmetry was found in both the CO2 and H2O. The CO2 is more prevalent in the southern coma, while the H2O is more prevalent in the sunward direction. The ratio of CO2 compared to H2O is over a factor of 2 larger in the southern, anti-sunward direction than in any other region. Further study of this asymmetry will give insight to the chemistry of the near-nucleus ambient coma as well as the anisotropic outgassing of the nucleus.

GRAVITY OR STRENGTH? AN INTERPRETATION OF THE DEEP IMPACT EXPERIMENT (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1068.pdf)


So, either gravity or strength craters can be consistent with the observations. Thus, the observations to date do not discern between the relative importance of strength and gravity in the DI event.

DEEP IMPACT: EXCAVATING COMET TEMPEL 1 (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1978.pdf)


The preliminary analysis of the data has already lead to significant, new understanding of cometary properties and behavior and this talk will summarize the present state of our understanding with details of some results in related talks.

WATER ICE ON TEMPEL 1: BEFORE, DURING, AND AFTER THE IMPACT EVENT (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1890.pdf)


Water ice was detected and mapped in all three phases of observations. We present the identification, spatial distribution, and particle size of water ice and trace its path during impact and in relation to the comet’s structure.

Others at: LPSC 2006: SPECIAL SESSION: RESULTS FROM THE DEEP IMPACT MISSION (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/sess453.pdf)

ToSeek
2006-Apr-04, 05:12 PM
The 250,000 Ton Punch (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1917&mode=thread&order=0&thold=0)


Over the weekend of 9-10 July 2005 a team of UK and US scientists, led by Dr. Dick Willingale of the University of Leicester, used NASAE28099s Swift satellite to observe the collision of NASA's Deep Impact spacecraft with comet Tempel 1. The Swift observations show that the comet grew brighter and brighter in X-ray light after the impact, with the X-ray outburst lasting a total of 12 days.

George
2006-Apr-04, 08:45 PM
The 250,000 Ton Punch (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1917&mode=thread&order=0&thold=0)


"The Swift observations reveal that far more water was liberated and over a longer period than previously claimed," said Dick Willingale.

Also, just curious, why are there two x-ray peaks in their graph - rotation?

Sticks
2006-Apr-05, 09:01 AM
Here is how this is reported on the BBC website (http://news.bbc.co.uk/1/hi/sci/tech/4871934.stm)

This extra water being given off, is it enough to change it's trajectory :neutral: The told us this would be safe :shifty:

ToSeek
2006-Apr-05, 02:20 PM
Here is how this is reported on the BBC website (http://news.bbc.co.uk/1/hi/sci/tech/4871934.stm)

This extra water being given off, is it enough to change it's trajectory :neutral: The told us this would be safe :shifty:

By my reckoning, even the 250,000 metric tons of water is less than a billionth of the total mass of the comet. It shouldn't make a significant difference.

Sticks
2006-Apr-05, 03:11 PM
I only mention this, because one of the ideas to steer rouge comets off of collision course was to use a large reflector to create a jet to nudge it onto a different heading.

01101001
2006-Apr-05, 04:56 PM
By my reckoning, even the 250,000 metric tons of water is less than a billionth of the total mass of the comet. It shouldn't make a significant difference.

And the 250000 tonnes total over the impact-related outburst duration, should be compared to the normal non-impacted rate of 16000 tonnes per day.

The 250,000 Ton Punch (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1917&mode=thread&order=0&thold=0)

Tempel 1 is usually a rather dim, weak comet with a water production rate of 16,000 tonnes per day. However, after the Deep Impact probe hit the comet this rate increased to 40,000 tonnes per day over the period 5-10 days after impact. Over the duration of the outburst, the total mass of water released by the impact was 250,000 tonnes.

Jerry
2006-Apr-06, 03:45 AM
The 250,000 Ton Punch (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1917&mode=thread&order=0&thold=0)
After seeing the plots, this is quite an incredible claim: All there is, is a shift in the background, a shift that never returned to the original baseline. They are integrating all the noise in this background shift, and calling it Deep Impact water. There is not even a hint of a Gaussian distribution. Baseline shifts can be anything from and including the solar wind, to calibration errors, to a dustier environment that may or may not contain copious amounts of moisture.

From Sticks reference:

"All this is supposition; all we know is that when we put in the numbers we seem to get an excess coming off of about two and a half times over the quiescent level."

No, they don't see anything "coming off", 'coming off' implies a rise, a distribution, a pattern, not a shift from the expected baseline.

Bad science!

George
2006-Apr-06, 01:35 PM
After seeing the plots, this is quite an incredible claim: All there is, is a shift in the background, a shift that never returned to the original baseline. They are integrating all the noise in this background shift, and calling it Deep Impact water. There is not even a hint of a Gaussian distribution. Baseline shifts can be anything from and including the solar wind, to calibration errors, to a dustier environment that may or may not contain copious amounts of moisture.
I am curious why their graph shows two peaks. Is this to be expected? Is the valley due to a leeward orientation (in the shadow)?

Jerry
2006-Apr-06, 02:15 PM
I am curious why their graph shows two peaks. Is this to be expected? Is the valley due to a leeward orientation (in the shadow)?
Good question - looking at the timing, the two peaks are both associated with the original plume. When I looked at the data, I assumed both of these peaks were picked up by other observers as well, because they are in the time frame very near to the impact. My guess is that as the heavier particles were pulled back by gravity, the lighter and gaseous elements became more exposed - the distribution should be more gaussian, but since the sampling times are hours apart, the true nature of the distribution is lost. If the conclusion of the Liecester scientists is based upon this second peak, and not the shift in the baseline, the conclusion is much more robust.

But if I am interpreting the articles correctly, they are doing a mole count in the baseline shift, AFTER the peaks desolved - they are integrating a much larger area than the initial (second) peak, and that is not valid. It is like measuring the grains of moisture in the air after a tyre burst, and saying "Oh, there is more moisture in the air now than there was before the tyre burst - that tyre must have been full of water."

George
2006-Apr-06, 03:37 PM
...if I am interpreting the articles correctly, they are doing a mole count in the baseline shift, AFTER the peaks desolved - they are integrating a much larger area than the initial (second) peak, and that is not valid. It is like measuring the grains of moisture in the air after a tyre burst, and saying "Oh, there is more moisture in the air now than there was before the tyre burst - that tyre must have been full of water."
Interesting. I would have guessed they would have taken their peak megawatt value and equate it to tonnage, but I am a novice on such things, admittedly.

Blob
2006-Jul-14, 07:12 PM
Scientists Gaining Clearer Picture of Comet Makeup and Origin

Scientists are getting their best understanding yet of the makeup of comets – not only of the materials inside these planetary building blocks, but also of the way they could have formed around the Sun in the solar system’s earliest years.

When NASA’s Deep Impact spacecraft slammed into comet Tempel 1 on July 4, 2005, the collision sent tons of pristine materials into space and gave astronomers from around the world, using ground- and space-based telescopes, the first look “inside” a comet. From that sample, over the past several months, scientists who used the imaging spectrometer on NASA’s Spitzer Space Telescope have refined their models of what a comet is made of and how it comes together.

"Spitzer’s spectral observations of the impact at Tempel 1 not only gave us a much better understanding of a comet’s makeup, but we now know more about the environment in the solar system at the time this comet was formed" - Dr. Carey Lisse of the Johns Hopkins University Applied Physics Laboratory.

Read more (http://www.jhuapl.edu/newscenter/pressreleases/2006/060714.asp)

Blob
2006-Jul-14, 07:21 PM
Title: Spitzer Spectral Observations of the Deep Impact Ejecta
Authors: C. M. Lisse, J. VanCleve, A. C. Adams, M. F. Ahearn, Y. R. Fernández, T. L. Farnham, L. Armus, C. J. Grillmair, J. Ingalls, M. J. S. Belton, O. Groussin, L. A. McFadden, K. J. Meech, P. H. Schultz, B. C. Clark, L. M. Feaga, J. M. Sunshine

Spitzer Space Telescope imaging spectrometer observations of comet 9P/Tempel 1 during the Deep Impact encounter returned detailed, highly structured 5 - 35 µm spectra of the ejecta. Emission signatures due to amorphous silicates and carbon, and crystalline silicates, carbonates, phyllosilicates, PAHS, water gas/ice, sulphides were found. Good agreement is seen between the ejecta spectra and the material emitted from comet C/1995 O1 (Hale-Bopp) and the circumstellar material around the young stellar object HD100546. The atomic abundance of the observed material is consistent with solar and C1 abundances, and the D/G ratio was determined to be = 1.3. The presence of the observed mix of materials requires efficient methods of annealing amorphous silicates, and mixing of high- and low-temperature phases over large distances in the early proto-solar nebula.

Rea more (http://www.sciencemag.org/cgi/rapidpdf/1124694v1.pdf) (subscription, PDF)

RGClark
2006-Jul-18, 03:27 PM
We discussed on this forum before the observations of Lisse et.al. that the Deep Impact mission showed carbonates and clays within Temple I.
The results have now been published in Science:

Scientists Gaining Clearer Picture of Comet Makeup and Origin
by Staff Writers
Laurel MD (SPX) Jul 16, 2006
"From its orbit, Spitzer's infrared spectrograph closely observed the materials ejected from Tempel 1 when Deep Impact's probe dove into the comet's surface. Astronomers spotted the signatures of solid chemicals never seen before in comets, such as carbonates (chalk) and smectite (clay), metal sulfides (such as fool's gold), and carbon-containing molecules called polycyclic aromatic hydrocarbons, commonly found in barbecue grills or automobile exhaust on Earth.
"Lisse said the clay and carbonates were surprises because they typically require liquid water to make - and liquid water isn't found in the regions of deep space where comets form. Also surprising was the superabundance of crystalline silicates, material formed only at red-hot temperatures found inside the orbit of Mercury."
http://www.spacedaily.com/reports/Scientists_Gaining_Clearer_Picture_of_Comet_Makeup _and_Origin_999.html

Spitzer Spectral Observations of the Deep Impact Ejecta.
Published Online July 13, 2006
Science DOI: 10.1126/science.1124694
http://www.sciencemag.org/cgi/content/abstract/1124694v1


Bob Clark

Blob
2006-Jul-18, 06:16 PM
Hum,
see also this (http://www.bautforum.com/showthread.php?t=19336&page=7)

ToSeek
2006-Jul-18, 08:44 PM
Thread containing last two posts merged with this thread.

ToSeek
2006-Aug-08, 05:53 PM
How Pure Is the Comet? (http://skytonight.com/news/3491846.html)


When NASA slammed the Deep Impact probe into comet Tempel 1 on July 4th, 2005, researchers were searching for the oldest stuff in the solar system. They thought that, below its altered outer layers, the comet's nucleus might contain ice and dust unchanged since 4.5 billion years ago — our best link to the birth of our solar system.

But when a team led by Carey Lisse (University of Maryland) aimed the infrared Spitzer Space Telescope at the cloud of ice and dust that erupted from the collision, they were surprised. The team reports in the August 4th Science that the Tempel 1 debris was laced with carbonates and clays: two classes of minerals that, on Earth, usually form in the presence of liquid water.

For a comet, liquid water does not mean oceans and rivers. Instead, it implies groundwater or steam seeping through the interior sometime in the past, destroying or altering the original materials within.

"The detection of carbonates and clays is surprising," says Paul Weissman (Jet Propulsion Laboratory), a comet researcher not involved in the Spitzer study. "For some people, this makes comets more interesting, but for me it also means that some of the pristine record we have always touted as being within cometary nuclei may have been lost."

RGClark
2006-Aug-09, 04:15 AM
How Pure Is the Comet? (http://skytonight.com/news/3491846.html)

Given the observation of eruptions of liquid water on Enceladus, and the widespread speculation they may be due in part to radiogenic heating you would think it would at least be mentioned the prior theories that radiogenic heating might have allowed liquid water in comet interiors early in the Solar Systems history AND that this may have allowed conditions conducive to life within comets.
Just as importantly is the fact the theories of radiogenic heating in comets were not introduced arbitrarily but because carbonates and clays were already observed in carbonaceous meteorites, some if not all of which are believed to stem from comets.


Bob Clark

George
2006-Aug-09, 08:02 PM
Because of their much smaller size - therefore, much greater surface area to mass ratio - the specific heat transfer rate of comets might be too fast to allow much radiogenic heating. I'm only guessing this is so, however.

Jerry
2006-Aug-09, 09:48 PM
One of the problems we are running into, is that mission instrumentation has been designed based upon prior expections. No one is certain how to interpret the results, because, in the case, no one anticipated that dust would hide so much. In retrospect, an observer that stayed focused on the event instead of clamming up an hiding in order to sneak a peak later might have reveal much more.

The same is true of Cassini and Huygens: The material that is out there is defying the ability of the spectrometers sent to Titan to define it. I think it would bode well to assume we know less and observe more.