Ah, Pluto. The once-and-possibly-future planet that sits way out near the edges of our solar system has always been a curiosity for astronomers, and when NASA’s New Horizons probe passed by the frosty world back in 2015 it captured some truly stunning images along the way.
Those images have been studied in depth for years now, but they’re still revealing secrets about the dwarf planet. Recently, researchers tackled one particularly interesting feature they were able to spot in the images. At first, it appeared as though Pluto was sporting snow-capped mountain peaks akin to Earth, but after doing a bit more digging it quickly became clear that Pluto’s peaks aren’t frosted with water ice, but something much less pleasant.
In a study published in Nature Communications, researchers explain that a peculiar atmospheric process is responsible for the frosted tips of mountains on Pluto. However, the “snow” is actually methane frost accumulating on the peaks, rather than precipitation falling from high above.
“Pluto is covered by numerous deposits of methane, either diluted in nitrogen or as methane-rich ice,” the researchers write. “Within the dark equatorial region of Cthulhu, bright frost containing methane is observed coating crater rims and walls as well as mountain tops, providing spectacular resemblance to terrestrial snow-capped mountain chains. However, the origin of these deposits remained enigmatic. Here we report that they are composed of methane-rich ice.”
Rather than accumulating through a process that would produce falling precipitation as we see on Earth, the researchers suggest that the methane actually condenses near the summits of the mountains, freezing there and producing an aesthetic similar to what we see when we look at a mountain on our own planet.
But how can this be possible when Pluto’s surface temperature is absolutely freezing at nearly 400 degrees Fahrenheit below zero? Well, it’s because the dwarf planet’s atmosphere is essentially the opposite of Earth’s in terms of heat distribution. On Earth, the warmest air tends to be near the surface, and the higher you go, the cooler it gets. The opposite is true on Pluto, where the sun’s far-traveling rays actually warm the atmosphere more than the ground below.
Methane is at a higher concentration at the higher altitudes, and when that warmer gas comes into contact with a frigid peak it condenses and freezes, creating the appearance of a snow-capped mountaintop. It sure looks neat, but yeah, you probably wouldn’t have much fun skiing down them.