The bowl-shaped ridges in Pluto’s ‘bladed’ or ‘snakeskin’ terrain that resemble similar structures on Earth are composed largely of methane ice and are largely a result of dramatic climate change over long periods that triggered geological activity.
These jagged ridges likely formed as a specific kind of erosion wore away the surfaces, leaving dramatic crests and divides.
These sharp and spiky features, known as ‘bladed terrain’, were imaged by NASA’s New Horizons spacecraft when it flew by Pluto in July 2015.
Located at the highest altitudes on Pluto’s surface, these ridges can soar many hundreds of feet into the sky.
The team led by Jeffrey Moore, a research scientist at NASA’s Ames Research Center in California’s Silicon Valley, determined that formation of the bladed terrain begins with methane freezing out of the atmosphere at extreme altitudes on Pluto, in the same way frost freezes on the ground on Earth, or even in your freezer.
Structures similar to the bladed terrain, though only a few meters high, exist on Earth in high-altitude snowfields along the equator, and are known as penitentes.
"When we realised that bladed terrain consists of tall deposits of methane ice, we asked ourselves why it forms all of these ridges, as opposed to just being big blobs of ice on the ground," said Moore.
"It turns out that Pluto undergoes climate variation and sometimes, when Pluto is a little warmer, the methane ice begins to basically 'evaporate' away," Moore said.
Scientists use the term "sublimation" for this process where ice transforms directly into gas, skipping over the intermediate liquid form.
Through variations in Pluto's climate over millions of years, atmospheric methane froze onto high-elevation surfaces, then much later sublimated into gas.
Over long periods of time, this process eroded the surface, creating ridges, crests, and divides.
Knowing that methane is found in high-elevation areas, scientists can use the data returned by New Horizons to infer other areas around the planet where methane is also likely to be present.
Low-resolution images of areas on the non-encounter side show evidence of bladed terrain existing there as well.
These findings confirm Pluto has a highly dynamic geological history and will likely provide scientists with new insights into that history and evolution.
The researchers have published a paper describing their findings in the journal Icarus.