MODELING AN EXOGENIC ORIGIN FOR THE EQUATORIAL RIDGE ON IAPETUS
This study examines the cratering efficiency of the expected distribution of ring particles that would have been created from ejecta of early impacts on Iapetus to determine whether they could form a ridge on the surface of Iapetus. Assuming water ice for both projectile and target material, pi-scaling calculations suggest that extremely oblique impact angles are needed to add to ridge topography. These extreme impact angles reduce the cratering efficiency, adding material rather than eroding it during crater formation; further, material is likely to be excavated at low angles, leading to accumulation downrange as well. Because infalling debris is predicted to impact at extremely low angles, both of these effects might have contributed to ridge formation on Iapetus.
Infalling material will also deliver heat to the surface of Iapetus, which can lead to a weakening of the moon’s surface and near subsurface material. Using the CTH code from Sandia National Labs, hydrocode models of extremely oblique impacts are used to examine the heat generated by the infalling material to assess the plausibility of a thermally-weakened surface supporting a large surface ridge.