Ice in Micro Cold Traps on Mercury: Implications for Age and Origin

Evidence in radar, reflectance, and visible imagery indicates that surface and subsurface water ice is present inside permanently shadowed regions in the north polar region of Mercury. The origin of this ice and the time at which it was delivered to the planet are both unknown. Finding the smallest, most easily eroded ice deposits on Mercury can help answer these questions. Here we present evidence for volatiles trapped in cold traps of scales ∼ 1–10 m. We consider two possible delivery methods for these deposits: a gradual, slow accumulation by micrometeorites or solar wind implantation and an episodic deposition, either primordial or by a recent comet impact. We conclude that the mechanism that best explains the presence of volatiles in these micro cold traps is a comet impact that most likely occurred in the last ∼ 100 Ma.