The methane snowcaps located on Pluto’s mountains are quite unusual as they were formed in reverse – at least in comparison to the snowcaps found here on Earth.
NASA’s New Horizons spacecraft revealed some very interesting facts about Pluto when it passed by the planet in 2015 which included frozen methane and nitrogen in addition to finding evidence of ice water.
In an interview with Space.com, Tanguy Bertrand, who is a planetary scientist at NASA Ames Research Center in Moffett Field, California, as well as the lead author of the study, explained, “The bedrock of Pluto is made of water ice, but it is so cold that the ice is harder than rock,” adding, “The mountains on Pluto are made up of this cold hard water ice.”
This brings us to their most recent discovery of how the snowcaps may have formed from the top down instead of from the bottom up. The snowcaps were found on Pigafetta Montes and Elcano Montes which are located in the dark region along the equator that’s called Cthulhu. The summits of Pigafetta Montes measure almost 2.2 miles in height and their reflective snowcaps are present at around the one mile mark. This is actually the first time ever that this has been found in our solar system besides Earth.
It wasn’t know for certain whether the caps were created from frozen methane, frozen methane that was diluted with frozen nitrogen, or perhaps a combination of both possibilities. That’s when scientists decided to analyze the data collected by the New Horizons spacecraft in order to answer that question once and for all. And according to their results, the snowcap frost “is almost pure methane ice, with traces of nitrogen ice”.
As for how they formed, it is the complete opposite of what happens on Earth. Here, the snowcaps are created when moist wind rises up and cools down, causing the moisture to condense and form snow on the top of the mountains.
On Pluto, however, since the atmosphere is so thin, the sun heats it up so that the higher up you go, the warmer it is. With that being said, the “atmosphere has more gaseous methane at its warmer, higher altitudes, allowing for that gas to saturate and freeze directly on the mountain peaks tall enough to reach the enriched zone,” Bertrand explained, adding, “At lower altitudes, the concentration of gaseous methane is lower, and it cannot condense.”
Bertrand finished off by stating, “This discovery teaches us that there are still plenty of physical and dynamical processes out there in space that we do not know about, and that climates can be very different than that of Earth, despite forming similar landscapes.” Their research was published in the journal Nature Communications and can be read in full here.
A side-by-side picture of the snowcapped mountains of Pluto’s Pigafetta Montes and Elcano Montes compared to the Alps on Earth can be seen here.