[X] My Assistant

[Guest_BruceMoomaw_*]

Don Brownlee's response yesterday to two questions on Stardust:

Moomaw: "I see that NASA, in its next Discovery proposal, is going to allow proposals for extended missions for both Deep Impact and Stardust in the "Missions of Opportunity" category. A few years ago, you told me that it was extremely unlikely that it would be possible to use Stardust's coming Earth flyby to retarget it to any future comet or asteroid flybys simply because it will be almost out of maneuvering fuel. Have you since identified any possible targets for such a flyby?

"Also, regarding the peculiar craters on Wild 2: is a consensus being reached that they are indeed sublimation pits rather than impact craters -- and is it possible that the craters on Tempel 1 might also be sublimation pits, despite their more rounded slope profiles?"
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Brownlee: "We could have done another comet flyby, but this would have involved trajectory changes before the Earth return. This is a risk to our main mission and a risk that we chose not to take. It is likely that Stardust will pass near an asteroid in the near future, but we have not looked into this in any detail. The orbit will be smaller after the flyby and I am not sure how far it will go into the asteroid belt.

"The great depressions on Wild 2 are a real mystery because nothing like them was seen on any of the other 3 comets that have been imaged. The presence of normal-looking impact craters seen by Deep Impact indicates that old comet surfaces do retain normal looking impact craters. The features on Wild 2 might be ablation-modified craters or just odd craters, but absence on the other comets argues against this. Temple 1 clearly has a very old cratered surface; and in contrast, my belief is that Wild 2 has a young heavily modified surface. Why it would look so different from Halley, a very active and presumably highly altered surface, is unknown.

"It is possible that Wild 2 had an earlier history closer to the Sun that created these features. It is also possible that comets are just a diverse bunch."
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Now, since the only asteroid-relevant instrument Stardust will have left after the flyby is a camera -- and one without a working color filter wheel -- it is seriously doubtful whether a simple photographic flyby of one near-Earth asteroid would be worth even the relatively small sum for an extended mission. Still, you never know for certain.