Study Says Mercury Gained Polar Ice in 176 Days From 97-Km Hokusai Impact
Updated
Updated · starlust.org · May 27
Study Says Mercury Gained Polar Ice in 176 Days From 97-Km Hokusai Impact
4 articles · Updated · starlust.org · May 27
A new planetary study argues Mercury’s polar water ice could have been emplaced within one Mercurian day—176 Earth days—rather than built up gradually over time.
Models tied that delivery to the 97-km Hokusai crater impact, which may have created a temporary water-rich atmosphere in under an hour and funneled vapor into permanently shadowed polar regions.
The simulations found a Hokusai-scale collision could deposit about 2.3x10 kilograms of ice, roughly matching the lower end of estimated polar ice mass, with atmospheric self-shielding helping more water survive photolysis.
The same models produced deposits only up to 37 centimeters thick, far short of the several-meter radar-bright ice inferred from observations, suggesting a larger, slower impactor may be needed.
Researchers said future work must include other volatiles, while ESA-JAXA’s BepiColombo mission could clarify the ice’s thickness and distribution.
As BepiColombo nears, can it solve why Mercury's ice is thicker than impact models predict?
Did one massive impact deliver all of Mercury's water ice in just a single Mercurian day?
Why does scorching Mercury have polar ice caps while the Earth's barren Moon does not?
Rapid Ice Delivery on Mercury: The Hokusai Crater Impact and the Origin of Polar Water Deposits
Overview
Mercury’s polar regions contain extensive water ice deposits, preserved in permanently shadowed craters that act as natural cold traps. While NASA’s Messenger mission confirmed these deep ice layers, the origin of the ice remained a mystery. A 2026 study provided a breakthrough by modeling how a single, large impact—the one that formed the Hokusai crater—could have rapidly delivered most of Mercury’s polar water. The impact vaporized water, which then migrated and froze in the cold traps. This new explanation connects the crater’s formation to the presence of ice, helping solve a long-standing planetary puzzle.