Mercury’s Polar Ice: How Billions of Tonnes Stay Frozen in Eternal Shadow
TL;DR Summary
Mercury can reach about 430°C in sunlit areas, but its poles host billions of tonnes of water ice tucked in permanently shadowed craters. The planet’s near-absence of atmosphere and the geometry of crater shadows keep these deposits cold and insulated, so they persist rather than melt. The ice is likely delivered by comets, water-rich asteroids, or solar-wind interactions over time, not formed in place. MESSENGER measurements suggest a mass range from about 20 billion to 1 trillion tonnes, and the upcoming BepiColombo mission should refine these figures. The ice is better viewed as a frozen archive of volatile delivery rather than a subsurface ocean.
- How does the closest planet to the Sun, with a surface that hits 430 degrees at noon, hold on to billions of tonnes of ice that never melt? Space Daily
- Deep inside polar craters on Mercury, sunlight has never once fallen — and NASA's MESSENGER spacecraft confirmed in 2012 that those permanently shadowed floors hold ancient water ice, sitting metres from terrain hot enough to melt lead Space Daily
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