Astronomy: How methane frost forms on Pluto’s mountain tops

Methane frost on mountain tops in Pluto's equatorial region is formed by a unique atmospheric process that differs from that forming the snow-capped mountains on Earth, reports a study in Nature Communications this week.

Pluto hosts numerous methane deposits and the ones observed on crater rims, walls and mountain tops in the Cthulhu region resemble the snow-capped mountain chains on Earth. However, the exact composition of these frosts (whether they are methane-rich or a combination of nitrogen and methane) and the mechanism by which they are formed was unclear.

Tanguy Bertrand and colleagues used data acquired by the New Horizons mission and performed high-resolution numerical climate simulations to understand the methane cycle on Pluto.

The authors demonstrate that the bright frosts observed in Pluto’s Cthulhu region are mostly made of methane-rich ice. Based on their simulations, they suggest that a circulation-induced enrichment of gaseous methane at high altitudes favour methane condensation on mountain summits and thus the formation of the observed frosts. This is in contrast to the terrestrial process where moist wind rises upslope and cools (due to the decrease with altitude of atmospheric temperatures induced by the expansion of the air in upward motions), triggering water condensation and snow formation on the top of mountains

The Plutonian process may be responsible for the formation of other methane-rich areas on Pluto, they conclude.