[X] My Assistant

[Guest_AlexBlackwell_*]

Wing Ip just had an interesting Iapetus-related paper published in GRL.

[ngunn]

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.

[ugordan]

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.