Pluto’s Mountains

The bright frosts observed in 2015 in the equatorial region of Cthulhu on Pluto are mostly made of methane-rich ice, according to new research.

This image, taken by NASA’s New Horizon spacecraft in 2015, shows the Pigafetta Montes mountain range on Pluto; the colorization on the right indicates the concentrations of methane ice, with the highest concentrations at higher elevations in red, decreasing downslope to the lowest concentrations in blue. Image credit: NASA / JHUAPL / SwRI / NASA’s Ames Research Center / Daniel Rutter.

“Pluto is covered by numerous deposits of methane, either mixed with nitrogen or as methane-rich ice,” said Dr. Tanguy Bertrand of NASA’s Ames Research Center and the Laboratoire de Météorologie Dynamique at Université Paris and colleagues.

“Within the dark equatorial region of Cthulhu, west of Sputnik Planitia, bright frost containing methane is observed coating crater rims and walls as well as mountain tops, providing spectacular resemblance to Earth’s snow-capped mountain chains.”

“However, the origin of these deposits is enigmatic,” they added.

Using data from NASA’s New Horizons spacecraft, the researchers developed a 3D model of Pluto’s climate.

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.

This process not only creates the methane ice caps on Pluto’s mountains, but also similar features on its crater rims as well.

The mysterious bladed terrain that can be found in the Tartarus Dorsa region around Pluto’s equator is also explained by this cycle.

“It is particularly remarkable to see that two very similar landscapes on Earth and Pluto can be created by two very dissimilar processes,” Dr. Bertrand said.

“Though theoretically objects like Neptune’s moon Triton could have a similar process, nowhere else in our Solar System has ice-capped mountains like this besides Earth.”

The study was published in the journal Nature Communications.

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T. Bertrand et al. 2020. Equatorial mountains on Pluto are covered by methane frosts resulting from a unique atmospheric process. Nat Commun 11, 5056; doi: 10.1038/s41467-020-18845-3