Pluto is a mysterious world. Located on the fringes of our solar system, beyond the orbit of Neptune, the dwarf planet is caked in exotic ice formations unlike anything we’ve ever seen — either on Earth or on other planets that we’ve explored so far.
These strange icy structures, dubbed “washboard” and “fluted” terrains, consist of a series of frozen ridges aligned in parallel with each other — all bizarrely oriented in the same direction, from east-northeast to west-southwest.
The peculiar landforms are mostly concentrated on the border of Sputnik Planitia, an ancient basin of nitrogen ice plains commonly referred to as Pluto’s “heart” due to its evocative shape, imaged here by NASA’s New Horizon spacecraft.
Stretching along the northwest margin of the basin, these distinctive landscapes “are among the most enigmatic landforms yet seen on Pluto,” argues a recent paper, published on Monday in the journal Nature Astronomy. The document is a letter authored by Oliver White, a scientist at the SETI Institute, who took an in-depth look at the washboard and fluted terrains on Pluto to understand how they came to be.
Working together with scientists from NASA’s Ames Research Center, White examined the shape and dimensions of the intriguing landforms and discovered new clues about their origin. According to their findings, these distinctive formations, which are unique to Pluto, may have formed during an “ancient glaciation” period in the dwarf planet’s distant past, reports Phys.org.
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The team looked at images from the New Horizons spacecraft — which in 2015 performed a historic flyby of Pluto and its moon Charon, as previously reported by the Inquisitr — and used them to map the washboard and fluted terrains discovered on Pluto. Their effort, coupled with topographic maps previously created from New Horizon data, revealed that these features occur at specific locations near the edge of Sputnik Planitia.
“Washboard terrain occurs in level topographic settings within valley floors, basins, and uplands, while fluted terrain is seen on steeper spurs, massifs, and crater walls that separate basins and valleys,” explains NASA. “These terrains occur at the location on Sputnik Planitia’s perimeter where elevations and slopes leading into the surrounding uplands are lowest, and also where a major tectonic system coincides with the edge of Sputnik Planitia.”
This has prompted the scientists to speculate that the frozen ridges outside of the basin were formed after a major surface change on Pluto, fueled by the movement of its tectonic plates. This event likely occurred before the creation of the Sputnik basin — which appeared roughly 4 billion years ago, when a giant asteroid crashed into Pluto.
At the time, the area was covered in nitrogen ice glaciers, which subsequently disappeared, giving way to elongated sublimation pits — depressions in Pluto’s surface created where ice turns directly into a gas. Once the glaciers retreated, the leftover nitrogen ice debris accumulated at the edge of the basin — which is found at lower altitudes than the surrounding terrain — thereby giving rise to the puzzling ice formations.
“After the nitrogen ice receded via sublimation, the debris was left as the aligned ridges — washboard where deposited on flat terrain and fluted where deposited on steeper slopes,” notes NASA.
Their specific orientation, which occurs consistently in all these landforms, suggests that the phenomenon responsible for their creation was a global-scale process.
“These terrains constitute an entirely new category of glacial landform that is unique to Pluto, and represent geological evidence that nitrogen ice glaciation was more widespread across Pluto in its early history prior to the formation of the Sputnik basin,” concludes White.