Ceres's obliquity history and its implications for the permanently shadowed regions

Abstract

Due to the small current obliquity of Ceres (ε≈4°), permanently shadowed regions (PSRs) exist on the dwarf planet's surface. Since the existence and persistence of the PSRs depend on the obliquity, we compute the obliquity history over the last 3 Myr and find that it undergoes large oscillations with a period of 24.5 kyr and a maximum of εmax≈19.6°. During periods of large obliquity, most of the present-day PSRs receive direct sunlight. Some craters in Ceres's polar regions possess bright crater floor deposits (BCFDs). We find an apparent correlation between BCFDs and the most persistent PSRs. In the north, only two PSRs remain at εmax and they both contain BCFDs. In the south, one of the two only craters that remain in shadow at εmax contains a BCFD. The location of BCFDs within persistent PSRs strongly suggests that BCFDs consist of volatiles accumulated in PSR cold traps: either water molecules trapped from the exosphere or exposed ground ice.