The Radiation Environment of Ceres and Implications for Surface Sampling.

Ceres is a large water-rich dwarf planet located within the asteroid belt. Its surface displays evidence of material sourced from a deep subsurface liquid brine layer within recent geologic time, making it a candidate ocean world with possible present-day activity. However, Ceres lacks a substantial atmosphere and likely does not possess a global magnetic field. Therefore, any material emplaced or exposed on the surface will be subject to weathering by charged particles of solar and galactic origin. We have evaluated the effect of charged particle radiation on material within the near-surface of Ceres and find that the timescale for radiation-induced modification and destruction of organics and endogenic material is ∼100 Myr to 1 Gyr within the top 10-20 cm of the surface. Furthermore, we find that the timescale for sterilization of any putative living organisms contained within material at these depths is <500 kyr. Future missions to the surface may therefore consider targeting regions with geologic ages that fall between these two timescales to avoid the risk of backward contamination while ensuring that sampled material is not heavily radiation processed.