The source of the significant water ice deposits hidden in Mercury’s polar regions has been a topic of debate among researchers. A new study, published in the Journal of Geophysical Research: Planets, suggests that these deposits were accumulated in only one Mercurian day (176 Earth days) by a large impactor, such as a comet or asteroid. While previous studies have suggested a similar scenario, this is the first study to fully model the impact. Furthermore, these new models suggest that the impactor may have been larger and slower than previously suggested.
Being the closest planet to the sun, Mercury sees daytime temperatures of up to 430°C (806°F). On top of that, Mercury doesn’t have a true atmosphere. Instead, it has an ultra-thin, tenuous layer of gas, called an exosphere, in which gases are constantly blown into space and then replenished by the solar wind. While these aspects of Mercury should make water retention extremely difficult, both Earth-based and orbital observations have found reflective areas that indicate the presence of water ice hidden in permanently shadowed regions (PSRs) near Mercury’s north and south poles.
Scientists have suggested several potential sources of the ice found in PSRs. Some hypotheses include steady delivery by micrometeoroids, solar wind, or a single large, volatile-rich impact. Some studies have found that the ice appears to be relatively pure and “young” (at only a few 100 million years). These findings suggest a rapid, episodic delivery rather than slow accumulation, according to more recent studies.
