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NASA Dawn Asteroid Mission Told to "Stand Back Up", Reinstated!
SFJCody
post Mar 29 2006, 08:01 PM
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Magnetometer or not, 2015 will put a significant capstone on humanity's exploration of the solar system: reconnaissance of the first KBO and the first main belt asteroid in the same year. 2016/2017 would be a good time to revise planetary textbooks.
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The Messenger
post Mar 29 2006, 08:05 PM
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QUOTE (AlexBlackwell @ Mar 29 2006, 12:04 PM) *
A couple of slightly outdated (from an instrument standpoint) references are "Dawn: A Journey In Space and Time" by Russell et al. and "DAWN: A JOURNEY TO THE BEGINNING OF THE SOLAR SYSTEM" by Russell et al.

If you have access to Planetary and Space Science, then a slightly more detailed mission description can be found here.

I also mentioned a recent Dawn-related article in Eos.

Thanks - these references are prefect. It will be interesting to compare these surfaces with Tempel I and Itowana.
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Guest_AlexBlackwell_*
post Mar 29 2006, 08:08 PM
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QUOTE (The Messenger @ Mar 29 2006, 08:05 PM) *
Thanks - these references are prefect. It will be interesting to compare these surfaces with Tempel I and Itowana.

You're welcome. And I presume you meant "Itokawa"?
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SFJCody
post Mar 29 2006, 08:10 PM
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QUOTE (The Messenger @ Mar 29 2006, 09:05 PM) *
It will be interesting to compare these surfaces with Tempel I and Itowana.


Perhaps Luna, Mars, Ganymede and Callisto will make better points of reference...
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Mariner9
post Mar 29 2006, 08:45 PM
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I second SFJCody's comment about a capstone event, but I would give it a slightly different slant.

With NEAR we got a look at the lower end of the mid-sized asteroids.

With Hayabusa we got a look at the smallest end of asteroids, and saw our first flying rubble pile

With Dawn, we will see 2 of the largest asteroids.

We will have completed our inital sampling of the asteroid belt.
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Guest_BruceMoomaw_*
post Mar 29 2006, 09:51 PM
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Actually, we still won't have done that. We have already seen three Main Belt asteroids -- one, Mathilde, fairly large, and two more (Gaspra and Ida) quite small; and Rosetta by 2010 should have flown by both little Steins and the quite large (100-km) Lutetia -- but that's still quite a limited set composition-wise. For instance, we will not yet have seen any M-types, or any of the distant D-types that are thought to be even richer in water and organics than the C types are (indeed, on the borderline between asteroids and comets).

Granted that this is assuming that Dawn -- which, at least earlier in its planning, had the potential to fly by several other asteroids during its cruises to Vesta and then to Ceres -- doesn't visit any of these types. But there is clearly such great compositional variety in the Belt (including WITHIN the overall asteroid "types") that it will be some time before we can honestly claim that we've seen a good sampling of it.
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SFJCody
post Mar 29 2006, 09:51 PM
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QUOTE (Mariner9 @ Mar 29 2006, 09:45 PM) *
I second SFJCody's comment about a capstone event, but I would give it a slightly different slant.

With NEAR we got a look at the lower end of the mid-sized asteroids.


...and Rosetta will give us a look at the upper end of the mid-sized asteroids.
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JRehling
post Mar 29 2006, 10:19 PM
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QUOTE (Mariner9 @ Mar 29 2006, 09:45 PM)
With NEAR we got a look at the lower end of the mid-sized asteroids.



QUOTE (SFJCody @ Mar 29 2006, 01:51 PM) *
...and Rosetta will give us a look at the upper end of the mid-sized asteroids.


Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.

-- Winston Churchill
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Mariner9
post Mar 29 2006, 11:00 PM
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Sigh. I considered putting in a caveate about the diversity of the asteroid belt, and just how many types of asteroids there are, and how a mere handful of asteroids does not fully represent the belt...

but I thought when I said "initial sample" that I might be conveying .. uh, "initial sample" as opposed to "exhaustive survey" or "good statistical representation of all major types"

Pardon me for not fully explaining that yes, I have indeed read several good texts and articles on asteroids, and yes, I know there are quite a lot of different types.

I suppose though, you just are not a full member of this forum until you've been corrected by the Moomaw.

Do I get my pin and certificate now?
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dvandorn
post Mar 29 2006, 11:01 PM
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QUOTE (Myran @ Mar 29 2006, 05:34 AM) *
...I worry somewhat, if this will still be within yelling distance? laugh.gif

Myran -- in space, no one can hear you yell...

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Guest_BruceMoomaw_*
post Mar 30 2006, 02:52 AM
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Actually, the Moomaw was just trying to point out that you can't even rightfully call it an "initial survey" until you've gotten at least one look at all the major types of asteroids -- and the M and D types definitely fall into that category. Asteroid size is less important than their composition.
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JRehling
post Mar 30 2006, 03:47 PM
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I have a long-standing belief that I haven't heard expressed explicitly, so I'll say it here: If we ever get to perform a close flyby of a very large number of asteroids, we would seem to be bound to find some interesting anomalies out there, even though most of those worlds are far too small to have their own dynamic thermal history. But with some permutation of parent bodies, impacts, and just plain the unexpected, and 10,000 chances, there have GOT to be some interesting freaks out there. Maybe an asteroid made primarily of some very rare element, like silver. Maybe a surface that has by statistical chance avoided taking any major impacts in 4 billion years. Maybe an asteroid that was last resurfaced by a single massive electrical discharge. Or one that is highly magnetized.

The above is specific-to-general thinking, but given the surprises you see just in the Saturnian satellites, it seems like a collection of bodies 1,000 times as numerous has got to have some inCREDible freaks among it.

Maybe one day we'll see some sort of solar powered/solar sail craft that has enough autonomy to go on arbitrary numbers of flybys and a fleet of them could visit a very large number of asteroids for not very much money; with longevity on their side, doing so for decades.

Some of those freaky finds would be just curiosities that don't tell us much about anything except the freak itself, but the right kind of find could be a major score for science; in principle, something like this could be more valuable than a mission to a major planet. The hitch is that any such discovery would be rear-loaded: It would probably come with no warning, and hence no opportunity for the given asteroid to ever be assessed by a boardroom full of planners as a worthy target. That's potentially a blindspot of planning methodology.
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Guest_Myran_*
post Mar 30 2006, 05:06 PM
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QUOTE
dvandorn said: in space, no one can hear you yell...


You havnt heard us two when we begin one argument and start yelling, its loud! So I worry that even 1 AU of vaccum would be a safe distance. tongue.gif

Back to being serious and re BruceMoomaw & JRehling, yes it would be interesting to have a look at avariety of asteroids and lest one of each type to see if our ideas derived from meteorites found on earth are correct or not.
Are these parts of a once larger 'moon sized' asteroid with a molten core that differentiated and broke up and gave us the various types. Yes moon sized meaning one smaller than Earths Moon, its unlikely it was larger, the total mass of the asteroid belt is to low to think a really larg object existed there.

Or was it another process in smaller asteroids like heating from impacts that caused some asteroids to be carbenous and others to have a high nickel iron content? The latter is perhaps less likely but cant be ruled out. A good survey might settle the question, so Dawn are a good start on doing that.
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JRehling
post Mar 30 2006, 05:12 PM
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QUOTE (Myran @ Mar 30 2006, 09:06 AM) *
Are these parts of a once larger 'moon sized' asteroid with a molten core that differentiated and broke up and gave us the various types. Yes moon sized meaning one smaller than Earths Moon, its unlikely it was larger, the total mass of the asteroid belt is to low to think a really larg object existed there.


The total mass of the main belt asteroids is less than the Moon, but it is still clear from meteorites (remember, we have tons of samples: in fact, some of the samples themselves weigh tons!) that there were larger parent bodies that were broken up significantly by impacts. I'd like to know how clear the picture is on which now-destroyed parent bodies may have existed. I know that it seems that Vesta is the (by far?) largest piece of a shatter event that has created some smaller named asteroids and no end of meteorites. And Vesta is large enough to have differentiated. But I don't know if we have a jigsaw-puzzle-solver's clue as to whether there were originally three such bodies, or five, or twelve, or ???
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Guest_BruceMoomaw_*
post Mar 30 2006, 06:31 PM
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One of the major mysteries of the belt is how Vesta -- which is pretty obviously one of the originally differentiated protoplanets in the Belt -- could have survived almost intact while almost everything else in the Belt was smashed into very small pieces by collisions. There was a recent piece of work by (I believe) Erik Asphaug proposing a time history of the Belt, and of the statistical distribution of different-sized fragments within it, that could explain how this happened. I'll track it down. (There is also Eric Nimmo's recent theory that Vesta may actually be a protoplanet from the inner-planet zone that wandered out into the Belt later on.)

Two other notes:

(1) The "EVE" mission Russell's team is proposing as a follow-up of Dawn would look at Hygeia -- which may be the biggest of the D-type asteroids -- and Psyche or some other M-type. This really WOULD allow us to complete our initial survey of the Belt.

(2) Even among the M types, however, there is currently a knock-down fight as to whether they really are all metallic. Some of them show signs of hydration, which implies that we may have wildly misinterpreted what they're made of -- they may be made not of nickel-iron, but of relatively low-temperature hydrated minerals. Others, however, DO seem from their near-IR spectra and radar reflectivity to be metallic.
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