The mechanism of formation and accumulation of water ice on the closest to the Sun and very hot planet is described.
Oddly enough, but the planet closest to the Sun is quite rich in ordinary water ice. It is believed that most of the water to Mercury, as well as to Earth, was delivered by asteroids. Some of it has survived in the eternal shadow of craters near the planet's poles. The temperature here stably remains deep below zero, although the part of the surface illuminated by the Sun can warm up above 400 ° C.
At the same time, such a contrast turns Mercury into an independent "chemical reactor" capable of producing its own water, which is also partially stored in the circumpolar regions of the planet. This is reported in a forthcoming article in the Astrophysical Journal Letters. The work of Professor Thomas Orlando's team is also highlighted in a press release released by the Georgia Institute of Technology.
The mechanism of ice formation is quite simple and was outlined in general terms back in the 1960s. However, now it was possible to apply it to the real conditions of a real planet with its complex surface, chemical and energy balance. According to this scheme, everything starts with the solar wind - a stream of particles that intensely bombards the planet's surface. It consists primarily of protons.
Interacting with minerals on the surface of Mercury, protons are able to bind with them, forming hydroxyl (OH) groups. In turn, hydroxyls can be released from molecules due to the high temperatures on the daytime side of the planet. Free OH groups interact with each other to form hydrogen and water molecules. Most of them escape into space or again disintegrate under the influence of the solar wind.
However, a certain amount manages to move to the circumpolar craters and hide in their cold shadow, where the Sun no longer looks. Without an atmosphere, the transfer of heat around the planet is difficult, and at the poles of Mercury, glaciers persist for entire epochs. Scientists estimate that over a period of three million years, such a mechanism is capable of accumulating about 11 billion tons of water ice, which is about 10 percent of the total amount on the planet.