Pluto’s Earth-like glaciers puzzle scientists
With heights up to 12, 218 feet (3,724 meters), some of Pluto’s mountain ranges stretch as high as New Zealand’s Alps. This was noted by NASA mathematical physicist Orkan Umurhan, who studied these unusual features and presented the results of his research to the 2018 scientific conference of the Committee on Space Research of the International Council for Science (COSPAR).
Pluto’s mountainous terrain shows surprising signs of glaciation–being covered by glaciers–and has visible gashes and valleys that spread like rays from points in its upper ridges. Some of the gashes appear to have been cut by glaciers now long gone.
“That’s exactly what you see in Yosemite,” said Umurhan, who works at NASA’s Ames Research Center in California. “It’s fascinating to see analogous processes happening with completely different materials, under completely different conditions, but eerily similar to what’s happening on Earth.”
All the glaciers currently seen on Pluto’s surface are located far below the mountain ranges, raising questions as to where they initially came from, and where they went.
Even more confusing, some of the glacial valleys are located in ancient terrains that are heavily cratered while others are in regions less than 100 million years old. In the latter areas, glaciation appears to have occurred for just a brief time before stopping.
Glaciers seen on Pluto today, in the lowlands far from the mountains, are composed mostly of frozen nitrogen, as opposed to glaciers on Earth, which are made of water ice. However, the glaciers sit in a bedrock of water ice that is as hard as granite.
Given Pluto’s low gravity and average temperature of minus 380 degrees Fahrenheit (minus 229 degrees Celsius), its glaciers should be far too hard to flow. They would need be significantly deeper and thicker like those on Earth to carve the valleys seen in the dwarf planet’s mountain ranges.
Furthermore, because nitrogen ice flows faster than water ice, glaciers in the mountain areas should have continually flowed and never built up to a depth capable of carving the valleys.
To explain these anomalies, Umurhan proposes Pluto may once have had significantly more methane than it currently does. New Horizons did find methane frost on high mountaintops. Scientists analyzing the data recently found evidence of methane dunes on the surface.
Methane can harden nitrogen ice much like carbon hardens water ice. If that hardening occurred, the ice could have built up at the base of the mountains instead of having flowed away.
To determine the effects of methane mixed into nitrogen ice, scientists would need to simulate these conditions in a laboratory, something that has not yet been done.
Much of Pluto’s methane may have been lost to space in a process similar to that which depleted the water on ancient Mars.
Nitrogen may regularly be redistributed on Pluto through a climate cycle that involves it evaporating from Sputnik Planitia, then later condensing and falling as snow on the mountaintops. This cycle may also include trace amounts of methane.
Umurhan theorizes that the ice in Sputnik Planitia, the left side of Pluto’s heart feature and location of most of the planet’s nitrogen glaciers, originated in higher elevations, from which it flowed downwards.
After the 559-mile (900-km) round basin was created billions of years ago by a giant impact, it was filled with ice that flowed into it from above, he proposes.
The crater-free Sputnik Planitia remains geologically active and may sit on top of a subsurface ocean.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.