Low effective ultraviolet exposure ages for organics at the surface of Enceladus

Abstract

AbstractThe saturnian moon Enceladus presents a remarkable opportunity in our solar system for searching for evidence of life, given its habitable ocean and plume that deposits organic-bearing ocean material onto the surface. Organic ocean material could be sampled by a lander mission at Enceladus. It is of interest to understand the amount of relatively pristine, unaltered organics present on the surface, given the ultraviolet (UV) and plasma environment. Here, we investigate UV penetration into Enceladus’s surface and the resultant effective exposure ages for various regions, using the UV reflectance spectrum of Enceladus as measured by the Hubble Space Telescope and considering the rate of resurfacing by plume fallout. In high plume fallout regions near the south pole, plume grains are buried by fresher grains within years, resulting in low levels of exposure to solar UV, which penetrates only ~100 micrometers. Regions at latitudes south of ~40°S can have exposure ages <100 years, translating to relatively high abundances of pristine organic material preserved in the regolith.