Shedding light on mysterious formations resembling giant knife blades of ice on Pluto, scientists have found that the “bladed terrain” is made almost entirely of methane ice, and likely formed as a specific kind of erosion wore away the surfaces, leaving dramatic crests and sharp divides. Among the many surprises that NASA’s New Horizons mission discovered when it flew past that distant world in July 2015, the strange “bladed terrain” had remained a mystery.
These jagged geological ridges are found at the highest altitudes on Pluto’s surface, near its equator, and can soar many hundreds of feet into the sky.The blades are related to Pluto’s complex climate and geological history, according to the study published in the journal Icarus. A team led by New Horizons team member 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.
“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.
Similar structures can be found in high-altitude snowfields along Earth’s equator, though on a very different scale than the blades on Pluto. This 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. 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. The findings suggest that the surface and air of Pluto are apparently far more dynamic than previously thought.