We all think of Mercury as a tremendously hot world, which it is, being the closest to the sun. However, it also has a surprising amount of ice for such a toasty little planet. Scientists have long puzzled over how all that ice got there, and a new analysis from the University of Georgia suggests that it’s the intense heat bombarding most of the planet that helps it manufacture ice.
The surface of Mercury is inhospitable, to say the least. The daytime temperatures reach 800 degrees Fahrenheit (427 degrees Celsius), and the nightside can hit -274 degrees Fahrenheit (-170 degrees Celsius). The frosty nightside isn’t where you’ll find ice, though. Despite its close proximity to the sun, Mercury is not tidally locked. So, all the middle latitudes get fried by the sun as it orbits. Instead, the planet’s vast ice reserves are concentrated at the poles.
NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft began its study of Mercury in 2011, quickly confirming the presence of ice at the poles. This confirmed older Earth-based radar observations. Mercury doesn’t have an atmosphere, so it was unclear how water would get to the polar regions.
The University of Georgia team speculates that it’s the lack of an atmosphere and the intense heat from the sun that results in ice formation. Since there’s no atmosphere to spread heat to the poles, they remain extremely frigid. Meanwhile, the sun bombards Mercury with protons (hydrogen nuclei). This causes the production of hydroxyl groups (hydrogen bound to oxygen) in the soil. The heat from the sun can also release hydroxyls from the soil and kick off a chemical transformation.
Two hydroxyl groups from the surface could combine to form water molecules.
When two energized hydroxyl molecules collide above the surface of Mercury, they would form a water molecule plus another hydrogen nuclei. Most of the water molecules would be blown apart by solar radiation, but some of it could end up settling at the poles. There, craters could shield it from the sun indefinitely.
The researchers estimate Mercury could produce 11 billion tons of ice over a period of 3 million years. That’s a lot, but it may only be 10 percent of Mercury’s reserves. The remainder could come from asteroid and comet strikes, similar to the ice present in craters on Earth’s moon.
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