At the equator of the distant dwarf planet Pluto lies a mountainous region, aptly named Cthulhu. Dark mountains would fit perfectly into the stories of HP Lovecraft. However, there are bright “caps” on the tops of these mountains and on the edges of the craters in this area. If it were on Earth, we would consider it snow.
At first, planetary scientists thought that the observed light formations in the mountains of Cthulhu formed similarly to Earth. It would not just be water, but methane, because we are talking about places where temperatures are around minus 200 ° C. But according to a recently published study, it’s different. There seems to be a process on Pluto that we have not yet observed on Earth or on other planets with which we already have some closer experience.
When the New Horizons images, which showed white formations in the Cthulhu area, were recently published, they immediately gained attention. However, it was not clear whether they consisted mainly of methane ice or rather a mixture of methane and nitrogen.
Methane ice with nitrogen
Tanguy Bertrand of NASA’s Ames Research Center and his colleagues claim in their new study that it is more or less pure methane ice, with a small amount of nitrogen.
Researchers believe that it is not a product of methane condensation, which would be similar to the condensation of water on Earth. According to them, the white peaks of the Cthulhu Mountains are a product of the stratification of Pluto’s atmosphere, where more methane is contained in the atmosphere at higher altitudes due to the flow. Methane ice should form at night, especially during the winter.
At lower altitudes, it evaporates again before the day. At altitudes of around 4 kilometers, however, there is more methane in the atmosphere and so much methane ice can form there overnight that part of this ice is kept solid during the day. When any methane ice appears there, the feedback mechanism is triggered. The bright surface reflects more incident radiation, so it cools – and more methane turns into ice at the site.