[X] My Assistant

[Guest_BruceMoomaw_*]

Looks like I have a siazable amount of crow to eat today on this mission -- but the same thing may be true of the mission's scientific advocates.

(1) Contrary to all my confident statements, it starts to look as though the impact actually vaporized very little ice from the comet's interior -- virtually all that huge ejecta cloud was simply dry, very fine surface dust kicked into space by the impact itself. At any rate, that seems to be the case from both the craft's own observations and those of the SWAS satellite (which was roused from long-term hibernation for this particular mission):
http://www.jpl.nasa.gov/news/news.cfm?release=2005-113a
http://www.cfa.harvard.edu/press/pr0523.html

Jeffrey Bell will be delighted -- he was cackling to me right after the impact that the entire huge ejecta cloud could be explained by this alone. I didn't believe him. But, as he said at the time, this also calls the science rationale for the mission into still further question: it seems to make it even more certain that any impact which produced a crater big enough to be seen would also produce a cloud of ejecta big enough to completely blot it out from the main craft's cameras. About all we've really learned from this impact is that Tempel 1 has a very thick but very loose surface dust layer, as opposed to a thinner and/or cemented one -- and couldn't we have learned that just as well (and more besides) just from equipping the main craft with a radar sounder?

By the way, NASA TV didn't bother to cover today's DI press conference at all -- they were too busy covering really exciting stuff like the Shuttle...and...the ISS...ZZZZZZZZZZ

Where was I? Oh, yes:

(2) Ed Strick and Decepticon were right about the Impactor and I was wrong: during the final seconds of its descent, it did get clouted by two different particles big enough to throw it briefly off attitude. However, it also hit the surface at 25 degrees from the local vertical -- so, if its camera wasn't pointing directly down the line of approach, this would also have somewhat blurred its final photos as I suggested.

[Bob Shaw]

Bill:

I don't doubt that the plume is there!  It's the structures within it I'm thinking of - S&T (I think) ran an article four or five years ago about 'Moonbows' and other atmospheric phenomena and how they'd work in different atmospheres and with different crystals in the upper reagions of such atmospheres, and I was wondering if we're seeing what we think we are!

Bob Shaw

An interesting page on the Exploratorium site regarding this subject:

http://www.exploratorium.edu/mars/martiansnow.html

[Bob Shaw]

Could DI revisit the same comet in the future?

I'd say it's highly unlikely - the two objects are not remotely co-orbital, they just happened to be in the same place at the same time. The Japanese sampling mission, on the other hand, is c-r-e-e-p-i-n-g up on it's quarry and - like Eros/NEAR before it (or shepherd ring satellites, or the Apollo 12 S-IVB), would dance around it's target for as long as it wasn't pumped away or tidally disturbed. For DI to return to it's target might take a l-o-n-g time!

[Bob Shaw]

Here's some diagrams of the Hayabusa orbital path:

http://www.isas.jaxa.jp/e/enterp/missions/.../scenario.shtml

[Guest_BruceMoomaw_*]

No one has come up with any workable scheme to allow Deep Impact to reexamine Tempel 1 -- although it remains a real possibility that ANOTHER spacecraft might do so, and in fact there might be considerable scientific benefit in doing so. I think it likely that some kind of attempt to repeat CONTOUR's planned flybys of multiple comets is among the front-runners for the next selected Discovery mission, and it's very easy to visualize a repeat visit to Tempel 1 (or Wild 2, Borrelly or Churyumov-Gerasimenko) as being part of its itinerary.

[Bob Shaw]

See Bruce's earlier comments regarding the lack of primordial material - looks like not only was the plume all surface dust, but it didn't have much of a, well, deep impact...

http://www.spaceflightnow.com/deepimpact/050714eso.html

[ljk4-1]

See Bruce's earlier comments regarding the lack of primordial material - looks like not only was the plume all surface dust, but it didn't have much of a, well, deep impact...

http://www.spaceflightnow.com/deepimpact/050714eso.html

So what does this mean for the Rosetta lander? I know getting anything back from a comet's surface will be an achievement, but will it not sample nearly as much as scientists hope?

[chris]

So what does this mean for the Rosetta lander?  I know getting anything back from a comet's surface will be an achievement, but will it not sample nearly as much as scientists hope?

If a sample gets back, the science team will be delighted. They will be able to learn huge amounts from the sample, whatever it is. Remember in reality we know remarkably little about comets.

Chris

edit: In light of Doug's comment... er, whoops

[djellison]

Once they get samples back from Rosetta they'll learn a lot of things like..

How in hells name Rosetta brought a sample home when it's not a sample return mission

Doug

[Bob Shaw]

Once they get samples back from Rosetta they'll learn a lot of things like..

How in hells name Rosetta brought a sample home when it's not a sample return mission

Doug

Well, Cap'n, it's the fuel, see? A combination of laughing gas and tyre-rubber, one haha-boinggggg and you're home again. Anyway, who needs Earth-landing gear? Genesis did fine without it...

[Guest_BruceMoomaw_*]

I think LJK was just talking about "getting back" DATA from a comet's surface, not actual material. Certainly the extreme dustiness of Tempel shows that they will have to be careful about selecting the absolute best landing site for the Rosetta Lander. (By the way, why didn't they stick with its nice original name of RoLand instead of renaming it "Philae"?)

[djellison]

I HATE Philae - Roland was much better

Doug

[Comga]

No one has come up with any workable scheme to allow Deep Impact to reexamine Tempel 1 -- although it remains a real possibility that ANOTHER spacecraft might do so, and in fact there might be considerable scientific benefit in doing so.  I think it likely that some kind of attempt to repeat CONTOUR's planned flybys of multiple comets is among the front-runners for the next selected Discovery mission, and it's very easy to visualize a repeat visit to Tempel 1 (or Wild 2, Borrelly or Churyumov-Gerasimenko) as being part of its itinerary.

Remember that the nucleus of Comet Tempel 1 is rotating, with a period of about 42 hours. Because the rotation period of Tempel 1 is not known with infinite precision, it would be difficult at best to phase the arrival of a flyby spacecraft to garauntee imaging of the crater. If a flyby occured while the crater was in darkness, or on the terminator, or in the fraction of the sunlit area that is inevitably not seen, then it would just be another flyby. Repeat flybys are probably not as valuable as flybys of additional comets, like Boethin, in the proposed Deep Impact extended mission.

[Guest_BruceMoomaw_*]

It now turns out that they will probably never be able to see the impact crater at all -- due to a combination of the thick dust cloud and the HRI
deconvolution problem. Had it not been for the combination of both, they
could probably have seen it:

http://www.newscientistspace.com/article/d...met-crater.html

And determining the overall size of the impact crater, at least, was an absolute primary mission goal. So, for the third time in a row, we have a Discovery mission very seriously screwed up due to a design or assembly error. One can still hope that Stardust will succeed; but at the moment, the last totally successful one we've had was Lunar Prospector. (Which makes it even more interesting that
the Senate just voted to keep the Discovery cost cap at an artificially low $350 million, in order to continue funding Shuttle/Station -- although I don't know whether that provision will hold in the final House/Senate
compromise.)

[tedstryk]

Bruce, the jury is still out on this one. It often takes years for the really good science from a mission to be processed and digested. Perhaps they will find the crater, perhaps not. Is it dissapointing, yes, but there is still a lot of valuable science to be gleaned from this mission, despite its possible failure on one goal. I think you are starting to sound too much like Jeff Bell.