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Thread: Progress of Dawn in the solar system

  1. #331
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    Dr. Raymon has pictures from 19 Feb 15 in his latest discussion on how Dawn will enter Ceres orbit.

  2. #332
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    Quote Originally Posted by Lord Jubjub View Post
    Dr. Raymon has pictures from 19 Feb 15 in his latest discussion on how Dawn will enter Ceres orbit.
    Emily Lakdawalla take on the latest pictures. She has compared them with pictures of the same resolution of other moons of similar size.

    http://www.planetary.org/blogs/emily...s-geology.html

    Emily Lakdawalla states

    "I've been resisting all urges to speculate on what kinds of geological features are present on Ceres, until now. Finally, Dawn has gotten close enough that the pictures it has returned show geology. Before, we could clearly see craters; but everything has craters. Now, with the latest images taken on February 19, we can see the shapes of those craters, and begin to interpret what they mean about Ceres' interior and geologic history. But we shouldn't get carried away, because the images still have a pretty small number of pixels; at their original resolution, the visible disk is about 210 pixels wide.

    In fact, before I even go in to any interpretation, I want to prime my analytical eye with images of other worlds we've visited at similar resolution. Dawn is seeing Ceres for the first time much the way that the Voyager spacecraft gave us our first images of the icy moons of the outer solar system as geological worlds. So I dug in to the Voyager archives and pulled out images of icy moons similar in size to Ceres, with similar numbers of pixels across their disks. Five of the pictures below are different moons of Saturn and Uranus, and three of them are of Ceres. All are presented at their original resolution. Check them out and compare and contrast!"
    Last edited by selvaarchi; 2015-Feb-26 at 10:11 PM.

  3. #333
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    Could these bright spots on Ceres be ice volcanoes?

    http://spaceflightnow.com/2015/02/28...ice-volcanoes/

    The discovery of puzzling bright spots on Ceres, the Texas-sized world now being studied by NASA’s Dawn spacecraft, has scientists wondering whether the features could be plumes from volcanoes launching material into space.

    Scientists have detected evidence of ice volcanoes on Ceres with telescopes before, but Dawn’s approach to the dwarf planet will yield the first up-close imagery and data on the little world’s make-up and terrain.

    “Ceres’ bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin,” said Chris Russell, Dawn’s principal investigator based at UCLA. “This may be pointing to a volcano-like origin of the spots, but we will have to wait for better resolution before we can make such geologic interpretations.”

    Scientists believe Ceres could be covered in a crust of ice, perhaps encasing an underground ocean.

  4. #334
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    A new series of animated images of Ceres has just been released. Although only about 44% of the planet is illuminated, the images are spaced in time; all or most of its surface can be observed, as Ceres rotates before Dawn's camera.
    The brightest of the bright spots is very prominent in several of these images. It presents a squarish appearance, and still does appear to be properly resolved.
    It remains visible, even after Ceres' rotation has carried the crater in which it lies onto the unlit portion of the planet. The floor and even the rim of the crater are dark, but the bright spot can still be seen. Interesting how it could reflect light from within what appears to be a totally dark crater...
    Last edited by Ross 54; 2015-Mar-02 at 09:18 PM.

  5. #335
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    Quote Originally Posted by Ross 54 View Post
    A new series of animated images of Ceres has just been released. Although only about 44% of the planet is illuminated, the images are spaced in time; all or most of its surface can be observed, as Ceres rotates before Dawn's camera.
    The brightest of the bright spots is very prominent in several of these images. It presents a squarish appearance, and still does appear to be properly resolved.
    It remains visible, even after Ceres' rotation has carried the crater in which it lies onto the unlit portion of the planet. The floor and even the rim of the crater are dark, but the bright spot can still be seen. Interesting how it could reflect light from within what appears to be a totally dark crater...
    link to article and images, below:
    http://dawn.jpl.nasa.gov/feature_sto...et_Arrival.asp
    Sorry but when using your link I got this :

    The page cannot be found (Error 404 )

    I went to the Nasa site and got this new link :

    http://www.nasa.gov/sites/default/fi...es-gif-360.gif
    Last edited by galacsi; 2015-Mar-02 at 09:22 PM.

  6. #336
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    Thanks, Galacsi. I tried linking the URL of the NASA announcement, but it refused to work, so removed it. The image series you linked is the one to which I was referring.

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    Appreciated here too for the updates.
    A remote possibility - the white spots might be visible in the shadow because they are active erupting plumes reflecting light?

  8. #338
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    Water vapor plumes rising above the elevation of the crater rim, and catching the Sun, are a possibility. I wonder, though, why these would appear so compact and reflective. They don't seem to have a vertical component, when seen at an angle, as one might expect, or to disperse broadly.

  9. #339
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    I remark these brigh spots are clearly visible only with raking light( and low illumination ). They could be made of snow (Dirtty snow ? ) ,created by these wator plumes , or carbonates or other white salts whose origin could also be hydrothermal.

    But I would prefer them to be alien cities ,alas I will not put any money on this idea !

  10. #340
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    Quote Originally Posted by galacsi View Post
    I remark these brigh spots are clearly visible only with raking light( and low illumination ). They could be made of snow (Dirtty snow ? ) ,created by these wator plumes , or carbonates or other white salts whose origin could also be hydrothermal.
    I dunno, in earlier animation, the spot was visible in direct illumination. We are yet to see an animation of complete rotation of the (dwarf) planet.
    Map shows other bright features associated with impact craters, but the double spot still stands out.
    I don't think it's an active plume, it has been seen for years, so it should have spouted off huge amounts of material even if it was a weak one.
    As the double spot is proven real now (not an artifact), it kinda rules out that it is merely brighter material excavated by impact on an unusually tall central peak. I guess I like the salt hypothesis most at this point.

    Oh well...over six weeks for next set of better images...
    Last edited by Zartan; 2015-Mar-03 at 01:19 PM.

  11. #341
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    I find these bright spots puzzling as well. I did wonder if they might be erupting vents, but now I am not so sure. I am beginning to lean towards them being fresh deposits after a (relatively) recent eruption.

  12. #342
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    More from Emily Lakdawalla on Ceres and also from "universe Today"

    http://www.planetary.org/blogs/emily...e-a-guide.html

    NASA held a press briefing on the Dawn mission yesterday, sharing some new images and early interpretations of them. The new images include a total of 27 from the Rotation Characterization 2 sequence that I discussed last week, as well as their first global map made by combining these 27 images in a mosaic. I spent yesterday playing with these photos, trying to decide what to write about them. I see lots of things that intrigue me, and I'm looking forward to Dawn investigating them in more detail.

    There are lots of places where crater floors are not the shape I expect. There are lots of subtle linear topographic features that might not be related to craters, but it's hard to say. I'm hesitant to write about these subtly intriguing features, because I feel like I indulged in speculation enough in my previous post on Dawn's photos; it seems premature to try to draw any more conclusions.

    So instead of writing another lengthy post interpreting the images, I invite you to check out these photos yourself, and offer you some guidance on things to look for. First, just appreciate the full rotation animation. Take a moment to imagine yourself as Dawn, watching Ceres rotate leisurely below you over the course of its 9-hour day.
    http://www.universetoday.com/119235/...s/#more-119235

    As the Dawn spacecraft prepares to enter orbit around Ceres on March 6, the science team provided the latest images and a mission preview during a mission briefing on March 2. The images released yesterday show more of those unusual bright spots and lots of craters, and feature two new global views of Ceres: one spinning globe, and a a mosaic of a flat map-view of Ceres’ surface.

    But the most-talked about feature is the 90-km-wide (57-mile) crater with two bright spots.

    “These spots are extremely surprising and have been puzzling to the team and everyone that has seen them,” said Deputy Principal Investigator Carol Raymond. “The team is really, really excited about this feature because it is unique in the solar system.”

    Raymond added that the team will be revealing the true nature of spots with the public in real time as the spacecraft gets closer and is able to make a determination.

    So what is the leading theory on the bright spots?

  13. #343
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    We hear from the NASA press conference that cryovolcanoes are now considered improbable, as a source of the bright spot. It's said that exposed ice on the crater floor appears to be the leading explanation. We're also told that the bright spot faded out as it reached the terminator, in the latest series of photographs. This last seems a simplification of a more complex problem.
    The terminator is not a smooth line on a cratered world. Anyone who has observed the Moon carefully, with even a modest telescope knows this. The terminator is a rough, jagged line. Crater floors go into the darkness before crater rims; peaks stand out brightly, surrounded by blackness.
    This is true on Ceres, too. The bright spot is still bright when the floor of the crater surrounding it already appears dark.
    It might be suggested that an elevated area exits at the center of the crater, perhaps even a central peak, that catches the last of the Sun's light at twilight. This does not seem to be the case, though.
    Another piece of information from the press conference-- Such elevated terrain was looked for carefully, at the site of the bright spot, but nothing of the sort was found. This helps the argument against cryovolcanoes, but it also raises some questions-- how can exposed ice on a dark crater floor reflect light that isn't there? How can the thin, wispy sublimation of exposed ice, of the sort apparently observed on Ceres form such a dense, reflective, compact spot ?
    Last edited by Ross 54; 2015-Mar-04 at 06:14 PM.

  14. #344
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    I can't believe it's not next year or next month but two short days away now.

  15. #345
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    That's when Dawn has decelerated enough so that it will be going too slowly to escape. Dawn will continue to decelerate until about March 17, and will continue to overshoot Ceres for a few days more. It will then fall to Ceres and enter into an orbit around that asteroid early next month.

    I've taken some pictures from Mark Rayman's Dawn Journal, and then measured them. However, I am unable to upload the results of my measurements.

  16. #346
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    NASA Spacecraft Becomes First to Orbit a Dwarf Planet | NASA
    NASA's Dawn spacecraft has become the first mission to achieve orbit around a dwarf planet. The spacecraft was approximately 38,000 miles (61,000) kilometers from Ceres when it was captured by the dwarf planetís gravity at about 4:39 a.m. PST (7:39 a.m. EST) Friday.

    Mission controllers at NASAís Jet Propulsion Laboratory (JPL) in Pasadena, California received a signal from the spacecraft at 5:36 a.m. PST (8:36 a.m. EST) that Dawn was healthy and thrusting with its ion engine, the indicator Dawn had entered orbit as planned.

    "Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Marc Rayman, Dawn chief engineer and mission director at JPL. "Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home."
    Dawn Blog Ľ Dawn Journal | November 28 has some diagrams of its odd trajectory for this month.

    I got the news from NASA's Dawn Mission (@NASA_Dawn) | Twitter

  17. #347
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    Congratulations NASA

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    Can't wait for the new pictures.

    R


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  19. #349
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    Yay Dawn!

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    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  21. #351
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    When the Hubble Space Telescope photographed the bright spot in 2003-2004, it reportedly found it about 9 percent brighter than Ceres as a whole. Given Ceres' albedo of around 9.0 percent, that gives an albedo of ~ 9.8 % for the bright spot.
    Hubble also found the apparent diameter of the bright spot to be, conservatively, about 1/7 the diameter of Ceres, or about 85 miles. The bright spot was not well resolved, so the size and brightness figures were subject to revision, given better imagery.
    Now, thanks to Dawn, we have those better images. The apparent diameter of the bright spot is about 8 miles, based on the space it occupies in a crater of a diameter given as 57 miles.
    From this we can see that the apparent area of the bright spot has been reduced by ~ 113 times. Barring complicating factors, its albedo should also have increased 113 times, above that inferred from the Hubble data. 113 times an albedo of 9.8 gives an albedo figure of just over 1000 percent. Anything above 100 percent albedo would seem to indicate not a reflective object, but a source of light, on its own account.

  22. #352
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    Quote Originally Posted by Ross 54 View Post
    When the Hubble Space Telescope photographed the bright spot in 2003-2004, it reportedly found it about 9 percent brighter than Ceres as a whole. Given Ceres' albedo of around 9.0 percent, that gives an albedo of ~ 9.8 % for the bright spot.
    Hubble also found the apparent diameter of the bright spot to be, conservatively, about 1/7 the diameter of Ceres, or about 85 miles. The bright spot was not well resolved, so the size and brightness figures were subject to revision, given better imagery.
    Now, thanks to Dawn, we have those better images. The apparent diameter of the bright spot is about 8 miles, based on the space it occupies in a crater of a diameter given as 57 miles.
    From this we can see that the apparent area of the bright spot has been reduced by ~ 113 times. Barring complicating factors, its albedo should also have increased 113 times, above that inferred from the Hubble data. 113 times an albedo of 9.8 gives an albedo figure of just over 1000 percent. Anything above 100 percent albedo would seem to indicate not a reflective object, but a source of light, on its own account.
    I don't think that's how it works. Albedo of the 8 mile area would be determined by the ratio of incoming light vs light reflected, with more than 100% return indicating a light source. I don't think that its correct to assume that if a given spot's area is found to be greatly less, then the previously measured albedo would be proportionally more.

    showing that these spots are not light sources is trivial: simply measure if the brightness falls off as the spot rotates out of the direct sunlight. we should see a measurable drop off as it crosses the terminator. I would imagine this has been done repeatedly, and if it were a light source, it would be headline news.
    Last edited by iquestor; 2015-Mar-08 at 06:55 PM.

  23. #353
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    As I understand it, for a reflected light output of a given intensity, the smaller the area of the reflector, the greater the albedo, or reflective efficiency it must have, in proportion. I have read that in observing distant asteroids they estimate the diameter based on a reasonable albedo for such a body. If they can ascertain that the albedo is higher, they adjust the diameter estimate downward.

    It's been said that the bright spot on Ceres disappears when it reaches the terminator. That seems a simplification of a more complex problem. The terminator is far from being a smooth line, on a cratered world. Low areas, like crater floors pass into darkness before their rims do.
    In some recent images of Ceres, the floor of the crater in which the bright spot lies can be seen to be in darkness, yet the bright spot can still be seen. It appears to become invisible only when geometric foreshortening causes the source, which seems to have no vertical component, to appear edge on from our point of view.

  24. #354
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    Quote Originally Posted by Ross 54 View Post
    As I understand it, for a reflected light output of a given intensity, the smaller the area of the reflector, the greater the albedo, or reflective efficiency it must have, in proportion. I have read that in observing distant asteroids they estimate the diameter based on a reasonable albedo for such a body. If they can ascertain that the albedo is higher, they adjust the diameter estimate downward.

    It's been said that the bright spot on Ceres disappears when it reaches the terminator. That seems a simplification of a more complex problem. The terminator is far from being a smooth line, on a cratered world. Low areas, like crater floors pass into darkness before their rims do.
    In some recent images of Ceres, the floor of the crater in which the bright spot lies can be seen to be in darkness, yet the bright spot can still be seen. It appears to become invisible only when geometric foreshortening causes the source, which seems to have no vertical component, to appear edge on from our point of view.
    I think what you are saying is true for known light sources but doesn't make sense to me (an amateur) for measuring or determining albedo for an area on the surface of a body.
    perhaps it does when finding the albedo of an entire body, but not a smaller area. (I could be wrong on this).

    I haven't seen the images you refer to, but for a bright reflective spot on the bottom of a crater, they would seem to be a lot of reasons why the reflection might persist momentarily, due to uneven surfaces reflecting light at angles, etc. Since Dawn is orbiting Ceres, the area can be (an I am sure, has been) viewed on the dark side, which would quickly show whether it was an actual light source rather than reflected light.

  25. #355
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    I'm having trouble imagining how a reflective surface at any angle, on the floor of the bright spot's crater, can reflect light, when that crater floor lies in darkness.
    As I understand it, Dawn had been approaching Ceres from the lighted side. I've also read that Dawn must currently be repositioned in order to photograph the surface of Ceres, then back again to communicate with Earth. They use a limited supply of hydrazine fuel to do this. They report being highly conservative in their use of this fuel.
    I suspect they would avoid using this fuel to image what was expected to be a dark, featureless surface. Then, too, once Dawn came around to the unlit side of Ceres, the Sun was lying in about the same direction as the planet. They reportedly want to avoid photography under these conditions, so that excessive light from the Sun can not damage the camera.
    I've not seen any images of the unlit side of Ceres, other than the last two with both lighted and dark portions shown. One of these shows the bright spot surrounded by darkness. It's unclear that the other includes that portion of the surface which contains the bright spot.

    On a separate point-- I apparently introduced some errors, in my attempt to compare the Hubble Space telescope images to those from Dawn. I now prefer this calculation: The difference between the albedo of Ceres background, and the bright spot, multiplied by the reduction in its apparent area afforded by Dawn's better imagery. This generates an albedo figure of .9 As this must be divided between two spots of unequal brilliance, I adopted the albedo figures of approximately .6 for the brighter, and .3 for the dimmer of the two spots.

    The figure for the brighter of the two is still well above that of the sort of ice we might expect to find on Ceres. It's not too far from NASA' current figure of .4
    In any case, all these size estimates and albedos are quite tentative. The bright spots are still optically unresolved. They very likely appear larger and dimmer than than will when better imagery becomes available.
    Last edited by Ross 54; 2015-Mar-09 at 05:53 PM.

  26. #356
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    You are also looking at uncalibrated images, with unknown clipping points in the histograms for the currently released images. I feel like you're skirting either ATM or CT ideas here. Any claim that "something" must be generating light at Ceres' surface must be viewed as an extraordinary one. What are you trying to say here? You are trying to use precise calculations on uncalibrated, radiometrically clipped and possibly compressed images. This has a high probability of failure.

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  27. #357
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    I'm not challenging any established scientific theory, nor asserting that there is a conspiracy to withhold information from the public. I am merely considering some (to me, at least) interesting questions, and possibilities raised during the exploration of a world very largely unknown to us. I attempt to use the best information that I know to be available to me.
    I am content to leave with the moderators of this forum any discussion, or decision bearing on where my posts belong within this forum.

  28. #358
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    These bright spots are weird for sure. I'm glad they are saving the hydrozine for orbital use, no need to waste it long range. It's keeps us guessing for a while longer for the answers, a good mental exercise on the verge of discovery.

  29. #359
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    Marc Rayman comments on the lights in his newest blog entry:

    "For example, some people ask if those spots might be lights from an alien city. That’s ridiculous! At this early stage, how could Dawn determine what kinds of groupings Cereans live in? Do they even have cities? For all we know, they may live only in rural communities, or perhaps they only have large states."

    Looking at the animated .gif, the bright spots seem to disappear fairly quickly after the terminator, so they probably aren't active lights. Though, the animation has very low frame-rate.
    Of course, the actual brightness question is far from resolved: the history of observing the spot(s) has been that with every new observation, they have got smaller but brighter: no reason to assume we have reached the plateau right now. They are still overexposed and we can't observe any structure other than separation of bigger and lesser spot.
    Interestingly, my original hypothesis - that the spot is a very tall central peak of a crater - has apparently been ruled out.

    Just for giggles, here is an old artists' impression of Ceres, based on Hubble pics. Looking at Dawn pics, I'm thinking that Ceres should really have been visited long ago. I mean, better late than never, but even discounting the bright spots, the world seems to have lots of interesting things going on.

    In fact, entire asteroid exploration progress has been strangely bass-ackwards. We started visiting the tiny ones and gradually moved to the bigger ones - Lutetia, Vesta, Ceres...makes a nice suspense story but logically, it should have been other way around...

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    I enjoy Dr. Marc Rayman's blogs, they're very informative and accessible. He doesn't take himself overly seriously, and seems open to new possibilities.
    One notable feature of the Feb. 25th set of images is that the bright spot, surrounded by darkness, appears to undergo geometric foreshortening, as Ceres rotation carries it around the planet. It appears to flatten out, and only become invisible to us when it's presented edge-on. It does not appear to have any vertical component.

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