Pluto’s mountains are snow-capped, but not for the same reasons as...

In 2015, the New Horizons probe discovered spectacular mountains on Pluto with peaks covered in ice, strikingly resembling terrestrial massifs. Such a landscape had never been observed elsewhere in the Solar System. But, while on our planet the atmospheric temperatures decrease with the altitude, on Pluto, they warm with the altitude, because of the solar radiation. Where does this ice come from? An international team, led by scientists from the CNRS, carried out the investigation. They first determined that this “snow” from the mountains of Pluto is actually ice made from methane, a gas found in trace amounts in Pluto’s atmosphere, much like water vapor on Earth. Then, to understand how the same landscape could be produced under such different conditions, they used a model of the climate of the dwarf planet. This allowed them to discover that due to its particular dynamics, Pluto’s atmosphere is enriched with methane gas at altitude. Therefore, it is only at the top of mountains high enough to reach this enriched zone that the air is loaded enough with methane to allow its condensation. Lower down, the air is too poor in methane for ice to form. Posted in Nature Communications, this work could also explain why the thick methane glaciers observed elsewhere on Pluto are bristling with spectacular craggy ridges, unlike the water, flat, land glaciers.