Are there sand dunes consist of frozen methane on Pluto ?
– News of June 5, 2018 –
Pluto, the distant dwarf planet, is no longer so mysterious since it was flown over by the New Horizons space probe in the summer of 2015. The images from the surface have allowed us to observe a world with much more geological diversity than expected. Some of the geological formations observed on the surface of Pluto appeared only half a million years ago. Among these, an interuniversity team thinks they have identified sand dunes. In a study published in early June in the magazine Science, the team focuses on ripples located in the Sputnik Plain area, a large basin 1000 km wide covered with ice. West of this basin, near a mountain range, the New Horizons photos show polygons separated by dark borders. By observing these formations a little closer, we can see wrinkles, which immediately evokes the dunes observable on Mars. Along these wrinkles, one can also distinguish black trails all oriented in the same direction, as if they had been formed by the wind. But how could dunes have formed on Pluto ? The planet does not really shine because of golden beaches and its atmospheric pressure leaves little room for wind that could carry sand.
The hypothesis of the team at the origin of the study is that the sands of Pluto consist of small particles of methane ice of a few hundred micron each. These particles would be light enough to be transported by the strongest winds of the dwarf planet. These winds would form down mountains and it is precisely at the foot of a mountain range that the dunes were observed. If the winds of Pluto are strong enough to carry these grains of methane, they are not enough to raise them. This is where the phenomenon of Pluto’s ice sublimation works : when heated by the sun, the ice on the surface of the dwarf planet goes directly into the gaseous state. This sublimation could carry some grains of methane in its ascent. At a certain altitude, the winds of Pluto would take over and accumulate these sands in the huge dunes observed by New Horizons. Different phenomena can give rise to similar formations. The dunes of the Earth and Pluto do not have the same origin at all, and yet they look the same from space.
The dwarf planet is in any case the object of other studies by the researchers : another study published a few days ago proposed a hypothesis concerning the formation of Pluto. Comet 67P / Churyumov-Guerassimenko explored by the Rosetta Probe presents a composition strangely similar to the Sputnik plain glacier. This gives the impression that the small planet is the result of the agglomeration of comets. About 1 billion of them could have allowed Pluto to form. This differs from the usual model which assumes that Pluto would have formed directly in the protoplanetary disk and thus have a chemical composition quite close to the sun. It is still difficult to decide between the two hypotheses because none can fully explain the current composition of the dwarf planet. The Kuiper belt is still very mysterious. Maybe the overview of the 2014 MU69 object by New Horizons that will take place in a few months will bring new elements.
Image by NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute [Public domain or Public domain], via Wikimedia CommonsSources