Studying Sputnik Planitia, a large impact crater filled with ice of nitrogen, methane and carbon monoxide, the New Horizons probe observed polygonal shapes separated by small hollows on the surface of the ice. After several hypotheses that do not reach consensus, a team of French and British scientists suggests that convection movements, originating in the sublimation of nitrogen, could create these forms on the surface.
Located in the, is a telluric body with a very cold surface (-236 ° C on average), due to its very great distance from the (on average 39.5 AU, or nearly 6 billion kilometers). Its surface is covered with ices of water, methane, and of . This also has a composed of nitrogen, methane and carbon monoxide, a composition very close to that of surface ice. This atmosphere is very thin: the pressure on Pluto’s surface is only 15 µbars, or 100,000 times less than on Earth.
Interactions between surface ice and the atmosphere
The link between surface ice and the Plutonian atmosphere seems relatively well established: due to the action of theon the surface of Pluto, part of the ice present will sublimate (passage of the state at the ), enriching the Plutonian atmosphere with initially frozen compounds. Conversely, when the temperature drops, part of the atmosphere will condense to form ice on the surface. These sublimation / condensation cycles are also strongly impacted by the strong of the’ plutonian.
Amazing shapes on the ice surface of Sputnik Planitia
Since his firstof Pluto in 2015, the was able to capture images of many regions on the surface of the dwarf planet, including Sputnik Planitia, a large impact basin that was later said to have been filled with ices of nitrogen, methane, and carbon monoxide in minor proportions.
What attracted thescientists are the present on the surface of this mixture of ice, in the form of flat polygons delimited by small narrow hollows. Several hypotheses had already been proposed to explain these characteristics (flow of , temperature in the ice sheet), without any one being able to explain such a surface topography.
Sublimation of nitrogen involved
Thanks to many, the research team claims to have understood the mechanism behind these forms: due to the – transition from solid to gaseous state, without passing through the state – nitrogen on the surface of Pluto, local cooling causes from in layers of ice, thus reshaping its surface. The layer of ice would therefore be perpetually remodeled, according to the cycles of sublimation / condensation on the surface of Pluto.
According to the scientists of the study, such a dynamic could be observed on other regions of the surface of Pluto, or on the surface of other cold bodies, such as(satellite of ), or (one of the biggest bodies of the ).