Strange formations are found at the highest altitudes on the surface of the dwarf planet Pluto. They resemble giant knife blades of ice and can soar many hundreds of feet into the sky. According to new research published in the journal Icarus, these structures are made almost entirely of methane ice, and likely formed as a specific kind of erosion wore away their surfaces, leaving dramatic crests and sharp divides.
Pluto’s bladed terrain as seen from NASA’s New Horizons spacecraft during its July 2015 flyby. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
Lead author Dr. Jeffrey Moore, a member of the New Horizons team and a researcher at NASA’s Ames Research Center, and co-authors determined that formation of Pluto’s ‘bladed terrain’ begins with methane freezing out of the atmosphere at extreme altitudes (in the same way frost freezes on the ground on Earth).
“When we realized 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,” Dr. Moore said.
“It turns out that Pluto undergoes climate variation and sometimes, when Pluto is a little warmer, the methane ice begins to basically ‘evaporate’ away (a process called sublimation).”
Similar structures — called penitentes — can be found in high-altitude snowfields along Earth’s equator, though on a very different scale than the blades on Pluto.
The terrestrial penitentes are just a few meters high, with striking similarities to Pluto’s vastly larger bladed terrain. Their spiky texture also forms through sublimation.
In this extended color image of Pluto taken by NASA’s New Horizons spacecraft, rounded and bizarrely textured mountains, named the Tartarus Dorsa, rise up along Pluto’s day-night terminator and show intricate but puzzling patterns of blue-gray ridges and reddish material in between. This view, roughly 330 miles (530 km) across, combines blue, red and infrared images taken by New Horizons’ Ralph/Multispectral Visual Imaging Camera on July 14, 2015. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“The erosion of Pluto’s bladed terrain indicates that its climate has undergone changes over long periods of time — on a scale of millions of years — that cause this ongoing geological activity,” Dr. Moore and colleagues said.
“Early climatic conditions allowed methane to freeze out onto high elevation surfaces, but, as time progressed, these conditions changed, causing the ice to ‘burn off’ into a gas.”
“As a result of this discovery, we now know that the surface and air of Pluto are apparently far more dynamic than previously thought,” they said.
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Jeffrey M. Moore et al. Bladed Terrain on Pluto: Possible Origins and Evolution. Icarus 300: 129-144; doi: 10.1016/j.icarus.2017.08.031
