Dawn Survey Orbit Phase, First orbital phase |
Dawn Survey Orbit Phase, First orbital phase |
Jul 17 2011, 09:09 AM
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#1
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
I think it's time we start a new thread
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Jul 19 2011, 01:35 AM
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#2
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Member Group: Members Posts: 146 Joined: 31-October 08 Member No.: 4473 |
There is a big difference between Miranda and Vesta, however. The difference is the presence of ice and tidal forces on Miranda, both largely absent on Vesta.
Ice is quite ductile, and small gravity can cause it to flow, but plain rock, like on Vesta, don't flow unless it is pretty much hot enough to melt, and the interior pressures in Vesta, with it's light gravity, are not going to contribute that strongly. One of the big questions is how warm was the interior of Vesta at impact? We already know (pretty much) that Vesta got hot enough early to differentiate its core/mantle/crust, and then we can ask how much of this heat was left at impact. Since the planet as a whole did not re-spherize itself, it must have been largely cooled to a solid at impact time. Perhaps some of the core was still liquid -- radioactive decay might have kept it going a while. On the other hand, Quite some time might have passed since the planetary system formed and cleared out the nebula and most debris before the impact. We know that a significant amount of asteroidal objects are dynamically related to Vesta and are shards of the great impact. The surface of Vesta also does not appear to be crater-saturated. (With further imaging, crater counts should be able to give a rough age estimate -- looking forward to that.) So it seems (arms waving wildly) that the energy for reshaping parts of Vesta had to be delivered by the energy of impact. How much shock melting could accomplish is unclear, and a better answer is in the hands of the planetary modelers and the mega-computers. An interesting idea is the possibility that accumulated surface volatiles were stirred up by the impact and ablated by solar and impact heating, and Vesta was a giant comet for a while... Well, I think I've embarrassed myself enough for now. Its a free country, gotta love it. |
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