Amazingly, the New Horizons flyby (Hi, Pluto!) provided us with enough data to analyze for years. The latest paper to come out covers the ice on the mountains, which while similar to what mountains on Earth look like, aren’t the same at all.

In this study, scientists looked at the Pigafetta Montes mountain range, and they found that the concentrations of methane ice were highest at higher elevations and then those concentrations decreased downslope to the surface of Pluto. This methane-ice creates bright deposits.

So here on Earth, atmospheric temperatures decrease with altitude, because the air expands and cools as it moves upward. Now the atmospheric temps cool temperatures at the surface. When a humid wind approaches a mountain on Earth, the carried water vapor cools and condenses, clouds form and then we get snow on our mountain tops.

On Pluto, the process goes in the opposite direction. The atmosphere actually gets warmer as altitude increases because methane absorbs solar radiation and is more concentrated at those higher elevations. But the atmosphere isn’t thick enough to have an impact on the surface temps, which stay the same. And Pluto’s winds travel down the mountain slopes.

To understand the process, researchers did 3D simulations at the Laboratoire de Météorologie in Paris. Per the press release: They found that Pluto’s atmosphere has more gaseous methane at its warmer, higher altitudes, allowing for that gas to saturate, condense, and then freeze directly on the mountain peaks without any clouds forming. At lower altitudes, there’s no methane frost because there’s less of this gaseous methane, making it impossible for condensation to occur.

The process also explains the formation of penitentes — ice blades — around the rims of craters like those found in the Tartarus Dorsa region. 

More Information

NASA press release 

“Equatorial Mountains on Pluto are Covered by Methane Frosts Resulting from a Unique Atmospheric Process,” Tanguy Bertrand, François Forget, Bernard Schmitt, Oliver White &Will Grundy, 2020 Oct. 13, Nature Communications