Mountains of Pluto
may be formed on ‘bedrock’ of water-ice

Finding “youthful” mountains on the surface of Pluto has come as a great surprise to the Geology, Geophysics and Imaging (GGI) team studying the distant body since the New Horizons spacecraft flew past.

This image of mountains was taken by New Horizons just 1.5 hours before the spacecraft's closest approach to Pluto. Image Credit: NASA-JHUAPL-SwRI
This image of mountains was taken by New Horizons just 1.5 hours before the spacecraft’s closest approach to Pluto. // Image Credit: NASA-JHUAPL-SwRI

I was not planning to write anything about Pluto. After all, this blog is about water. Water on Mars is one thing. I did not expect to find relevance to a dwarf planet covered in frozen methane and frozen nitrogen.

But I can’t ignore the findings of scientists who studied images from New Horizons to announce a discovery of mountains rising as high as 11,000 feet and a region near Pluto’s equator that may still be geologically active. This conclusion comes from a lack of craters on the surface, said GGI team leader Jeff Moore of NASA’s Ames Research Center in Moffett Field, Calif.

One would expect that Pluto would be scarred from all the space debris falling to the surface over billions of years — unless recent geologic activity had erased the pockmarks, according to a report posted today by NASA.

“This is one of the youngest surfaces we’ve ever seen in the solar system,” Moore said.

Pluto has practically no gravitational interaction with another planetary body, which is believed to be why mountains have risen on the moons of giant planets. On Pluto, other forces must be at play.

“This may cause us to rethink what powers geological activity on many other icy worlds,” said GGI deputy team leader John Spencer of the Southwest Research Institute in Boulder, Colo.

The mountains are likely made of a water-ice “bedrock,” because frozen methane and frozen nitrogen are not strong enough to form mountains, the researchers say.

“At Pluto’s temperatures, water-ice behaves more like rock,” said deputy GGI lead Bill McKinnon of Washington University in St. Louis.

The scientists have been waiting nine years for New Horizons to reach Pluto, and now it is over. Yesterday, the spacecraft zoomed by at 30,800 miles per hour while seven instruments collected all sorts of information. Now all those data will be analyzed and discussed, adding to our knowledge of the solar system and beyond.

One mystery solved is the Pluto’s actual size — 1,473 miles in diameter — somewhat smaller than many earlier estimates. Pluto’s atmosphere complicated the estimates.

“The size of Pluto has been debated since its discovery in 1930,” McKinnon said in a report from NASA. “We are excited to finally lay this question to rest.”

The size revision means that Pluto is less dense than presumed earlier. The amount of ice in the interior is greater, and the lowest layer of the atmosphere — the troposphere — is shallower that once believed.

Pluto’s largest moon, Charon, lacks a significant atmosphere, so observations from New Horizons confirms previous estimates of 751 miles across.

The next two smaller moons were too small for researchers to estimate their size until now. Hydra appears to be about 30 miles in diameter, and Nix is about 20 miles across. Mission scientists believe that ice may be making their surfaces extra bright.

Pluto’s two smallest moons, Kerberos and Styx, are harder to measure but researchers expect to make estimates later.

Pluto and its largest moon, Charon, shown just above the Earth's surface in this graphic. Graphic: John Hopkins University APL
Pluto and its largest moon, Charon, placed just above the Earth’s surface in this graphic to show their relative sizes.
John Hopkins University Applied Physics Laboratory

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