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Fraser
2005-Jul-03, 08:18 PM
SUMMARY: NASA's Deep Impact spacecraft released its impactor "probe" Sunday morning, and changed its trajectory to pass a comfortable distance from Comet Tempel 1. When it was released, the impactor was 880,000 km (547,000 miles) away from Tempel 1. After releasing the impactor, Deep Impact began firing its engine for 14 minutes, which slowed down, and kept it out of the path of the onrushing comet. If all goes well, the impactor will strike Tempel 1 on Monday, July 4 at 0652 UTC (1:52 am EDT).

View full article (http://www.universetoday.com/am/publish/deep_impact_release_impactor.html)

What do you think about this story? Post your comments below.

dave_f
2005-Jul-03, 09:11 PM
If I read that right, the impactor will reach the comet a little before 1AM CDT tonight. Ooooo this is gonna be exciting. B)

Fraser
2005-Jul-03, 10:16 PM
Yeah, around 11:00 pm Sunday night my time.

om@umr.edu
2005-Jul-04, 12:19 AM
For a dissenting opinion on the importance of NASA's Deep Impact event, see NASA's Fireworks (http://www.physorg.com/news4899.html)

"Deep Impact is NASA’s big cosmic fireworks show for the Fourth of July, but they’re going to end up using smoke and mirrors to help validate this theory about a big cloud of dust that supposedly made the solar system."

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2005-Jul-04, 02:57 AM
Originally posted by om@umr.edu@Jul 4 2005, 12:19 AM
For a dissenting opinion on the importance of NASA's Deep Impact event...
I'm curious that the "scientist" who was quoted in that article seemed to imply that comets acquire sizable amounts of new material at some point in their elliptical orbits around the Sun. I'm guessing that the reported simply misunderstood the material in front of him.

It did seem kind of conspiratorial that this "scientist" is implying that the various people studying the results of Deep Impact are going to fudge the data to make it fit the current model of the Solar System.

dave_f
2005-Jul-04, 03:46 AM
I'm web streaming NASA's live coverage right now. :ph34r: Other than a minor oscillation problem in the antenna and a receiving station handover problem, things are all green. The auto-nav will be activated shortly.

om@umr.edu
2005-Jul-04, 04:09 AM
Originally posted by antoniseb@Jul 4 2005, 02:57 AM
. . . that article seemed to imply that comets acquire sizable amounts of new material at some point in their elliptical orbits around the Sun.
Yes, Anton, comets have lost material and aquired new material for billions of years as they moved along paths that traversed the inner and outer parts of the solar system.

That has been routinely reported with almost every news story about comets.

With kind regards,

Oliver
http://www.umr.edu/~om

dave_f
2005-Jul-04, 04:32 AM
The first auto-nav burn was successful, apparently. It lasted 22 seconds to nudge the impactor closer to the goal.

antoniseb
2005-Jul-04, 04:57 AM
Originally posted by om@umr.edu@Jul 4 2005, 04:09 AM
That has been routinely reported with almost every news story about comets.
I'd be interested in seeing some routine report that says they are currently still gaining materials. My understanding is that they gained their material during the formation of the Solar System, and have been losing material ever since.

Fraser
2005-Jul-04, 05:00 AM
Here's a cool link to nearly live images of the comet taken by Deep Impact. they're updating this page to show new images:

http://www.nasa.gov/mission_pages/deepimpa...ages/index.html (http://www.nasa.gov/mission_pages/deepimpact/images/index.html)

dave_f
2005-Jul-04, 05:18 AM
The second automated burn was successful. They are off by only one kilometer now from their intended target.

Half an hour to go.

om@umr.edu
2005-Jul-04, 05:20 AM
Originally posted by antoniseb@Jul 4 2005, 04:57 AM
My understanding is that they gained their material during the formation of the Solar System, and have been losing material ever since.
We know comets lose lots of material as they approach the Sun. That produces their "tails".

Comets are in highly elliptical orbits and naturally collide with lots of dust on their journey as they cross the orbits of planets.

It doesn't make sense to me to imagine that comets would not collect material.

If they managed to avoid accreting any material and continuously lost material since their birth, as you suggest, then comets must have been quite large initially - about the size of Jupiter?

I don't believe that.

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2005-Jul-04, 05:37 AM
Originally posted by om@umr.edu@Jul 4 2005, 05:20 AM
If they managed to avoid accreting any material and continuously lost material since their birth, as you suggest, then comets must have been quite large initially - about the size of Jupiter?
?!?!?!? No, whoever said that comets must have started out the size of Jupiter. The prevailing view is that they were about the size we see them now, and were flung out to the outer Solar System, and they come back in every once in a while in small numbers after some kind of disturbance. As to accreting new dust, It is possible that they collect small amounts of it, but that would be pretty trivial compared to the material lost. It is also likely, considering the low gravity of these objects that any dust hitting the comet would free an equal or greater amount of material from the comet.

I'm still waiting for you link to a routine report saying that comets gain materials.

dave_f
2005-Jul-04, 05:38 AM
The third burn was successful. Contact in 10 minutes.

om@umr.edu
2005-Jul-04, 05:56 AM
Originally posted by antoniseb@Jul 4 2005, 05:37 AM
1. The prevailing view is that they were about the size we see them now . . .

2. . . . any dust hitting the comet would free an equal or greater amount of material from the comet.

3. I'm still waiting for you link to a routine report saying that comets gain materials.
Hi, Anton.

1. If comets were initially the size they are now, and they accreted no material, then it follows that they lost no material.

2. If dust grains collected from the inner part of the solar system "free an equal or greater amount of material from the comet", then comets are a random mixture of material collected from different parts of the solar system. This is why they cannot be used to identify primordial building blocks of the solar system.

Meteorites that formed at the birth of the solar system are a much better source of information on the primordial building blocks.

3. I will not go searching through old news reports to provide you evidence that comets also collect material on their journeys. I have read that many times. If you can't find it in old news reports, try an astronomy textbook.

With kind regards,

Oliver
http://www.umr.edu/~om

Fraser
2005-Jul-04, 06:16 AM
Kabooom!

antoniseb
2005-Jul-04, 01:33 PM
Originally posted by om@umr.edu+Jul 4 2005, 05:56 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (om@umr.edu &#064; Jul 4 2005, 05:56 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-antoniseb@Jul 4 2005, 05:37 AM
1. The prevailing view is that they were about the size we see them now . . .
1. If comets were initially the size they are now, and they accreted no material, then it follows that they lost no material. [/b][/quote]
I did say ABOUT the same size they are now. The biggest fresh comets we see (for instance Hale-Bopp) have diameters around 40 kilometers. The largest dormant remains of old comets we see may have diamters in the ten to twenty kilometer range. This is different only be a factor of two, which is ABOUT the same size compared to your assertion that they must have originally been as large as Jupiter, which I was arguing against.

I understand your unwillingness to look for a routine report saying that comets gain materials. There are none.



2. If dust grains collected from the inner part of the solar system "free an equal or greater amount of material from the comet", then comets are a random mixture of material collected from different parts of the solar system. This is why they cannot be used to identify primordial building blocks of the solar system.

Impacting dust grains would only affect the first fraction of a meter of the surface of a comet, but yes, that surface would be a thin mixture of materials from the inner Solar System mixed with evolved material from the early days of the Solar System. It is a good thing then that Deep Impact blasted material from many meters down. Rosetta will tell us something about the amount of contamination. I expect it to be very low.

I agree that some probe landing on, exploring, and drilling a Kuiper belt Object would tell us with more accuracy and reliability what the early conditions were in the region of the giant planets and beyond. The Deep Impact probe was much cheaper, faster, and easier than that.

I look forward to seeing the results of the many studies.