On a ring origin of the equatorial ridge of Iapetus |
On a ring origin of the equatorial ridge of Iapetus |
Guest_AlexBlackwell_* |
Aug 29 2006, 06:18 PM
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Guests |
Wing Ip just had an interesting Iapetus-related paper published in GRL.
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Aug 31 2006, 10:00 AM
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Under the scenario proposed I would expect volatiles within the descending ring material to produce a temporary atmosphere around Japetus. Could this have provided sufficient drag to melt some of the infalling ices so that they fell as torrents of freezing rain or slush, solidifying pretty quickly on contact with the ground? I imagine this would produce a pretty hard ridge - a pile of 'cryolavas' rather than loose 'cryoregolith' - that would respond to subsequent (post-atmosphere) cratering similarly to the rest of the moon.
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Aug 31 2006, 11:18 AM
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Senior Member Group: Members Posts: 3652 Joined: 1-October 05 From: Croatia Member No.: 523 |
Could this have provided sufficient drag to melt some of the infalling ices so that they fell as torrents of freezing rain or slush, solidifying pretty quickly on contact with the ground? My guess is that due to Iapetus' weak gravity and thus low orbital velocity and also the fact it was probably spinning much more rapidly in the past, the impact velocity would be quite low as others have suggested. Probably too low for impact melting. If impact heating would be low, I'd guess the gentler drag through an atmosphere would heat up the particles even less, giving them time to cool. So once again, no significant melting. The stuff would fall down as it entered the "atmosphere", as dusty material. -------------------- |
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Aug 31 2006, 11:50 AM
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
My guess is that due to Iapetus' weak gravity and thus low orbital velocity and also the fact it was probably spinning much more rapidly in the past, the impact velocity would be quite low as others have suggested. Probably too low for impact melting. If impact heating would be low, I'd guess the gentler drag through an atmosphere would heat up the particles even less, giving them time to cool. So once again, no significant melting. The stuff would fall down as it entered the "atmosphere", as dusty material. I know these are just qualitative speculations with no hard numbers to back them up but I'm not convinced by this no-melting argument. There is no way of knowing the temperature or thickness of any temporary atmsphere formed and sustained by a catastrophic process like this. I would expect an atmosphere formed in this way to be hottest at the top and coolest at the surface (with possibly a very strong temperature gradient: note that Titan's upper atmosphere is remarkably warm even now). It would certainly have had a huge scale height due to the low gravity, probably extending out to the inner edge of the ring. Much would depend on the rate of infall of material. However it would surely have been significantly warmer than the current temperature of Japetus, conceivably warm enough to melt at least some volatiles even without the additional heat from friction. Add frictional heating and it's not hard to imagine a slushy equatorial blizzard growing the bulge layer upon layer, sort of stalagmite-fashion but by freezing rather than mineral precipitation. |
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