The mysterious "bladed terrain" of Pluto is made almost entirely of methane ice, and likely formed as a kind of erosion that wore away the planets surfaces, leaving dramatic crests and sharp divides, scientists say. NASA's New Horizons mission - which flew past Pluto in July 2015 - discovered the strange formations resembling giant knife blades of ice, whose origin 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, as high as a New York City skyscraper. They are one of the most puzzling feature types on Pluto, and it now appears the blades are related to Pluto's complex climate and geological history. A team led by Jeffrey Moore, a research scientist at NASA's Ames Research Center in the US has 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 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," 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," he said. This process is called sublimation where ice transforms directly into gas, skipping over the intermediate liquid form.
Similar structures can be found in high-altitude snowfields along Earths equator, though on a very different scale than the blades on Pluto. The findings, published in the journal Icarus, show that surface and air of Pluto are far more dynamic than previously thought. Identifying the nature of the exotic bladed terrain also brings us a step closer to understanding the global topography of Pluto, researchers said.
The New Horizons spacecraft provided spectacular, high- resolution data about one side of Pluto, called the encounter hemisphere, and observed the other side of Pluto at lower resolution. Since methane has now been linked to high elevations, researchers can use data that indicates where methane is present around Plutos globe to infer which locations are at higher altitudes. This provides an opportunity to map out altitudes of some parts of Plutos surface not captured in high resolution, where bladed terrains also appear to exist.
Though the detailed coverage of Pluto's bladed terrain covers only a small area, researchers have been able to conclude from several types of data that these sharp ridges may be a widespread feature on Pluto's far side, helping to develop a working understanding of Plutos global geography.