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Pluto’s glaciers change with its seasons

New Horizons captured this image of floating ices on Pluto’s surface. Image Credit: NASA/JHUAPL/SwRI

Using data returned by NASA’s New Horizons mission’s July 2015 Pluto flyby, a group of researchers discovered evidence that the dwarf planet’s glaciers expand and grow in response to seasonal changes.

Led by planetary scientist Helen Maynard-Casely of the Bragg Institute at the Australian Nuclear Science and Technology Organization (ANSTO), the researchers analyzed photographs of ice mountain peaks on Pluto’s surface and simulated conditions on that surface by using Wombat, a high-intensity neutron diffractometer at the Australian Center for Neutron Scattering (ANSTO).

Theirs is the first thermal expansion study of methane and nitrogen on Pluto.

In the simulation, they observed changes in the densities of both methane and nitrogen molecules in response to temperature changes. Pluto’s glaciers are composed of solid, frozen methane and nitrogen.

“Nitrogen actually has two crystal structures in the range of temperatures seen on Pluto. The nitrogen story is really interesting because the molecules have the ability to cool into an ordered structure, which is the alpha nitrogen phase, and at this point, there is a big volume drop…Whereas at a slightly higher temperature, around 44 Kelvin [minus 380.47 degrees Fahrenheit, or minus 229.5 Celsius], the nitrogen molecules are freely rotating in a plastic state,” Maynard-Casely reported.

Pluto’s hills of water ice flow on a sea of nitrogen. Image Credit: NASA/JHUAPL/SwRI

When Pluto’s temperatures warm, the methane and nitrogen molecules that make up its glaciers change their orientations and move, causing the glaciers to expand.

“In the warmer seasons of Pluto, still about minus 220 C, both the methane and nitrogen molecules are freely rotating in the solids–the molecules are not bound together very well. Studies of the mechanical properties of these materials at very low temperatures are really challenging, so we are missing useful information for the unusual conditions on the outer planetary bodies,” Maynard-Casely noted.

“The fact that methane and nitrogen molecules can flow at such extremely low temperatures has to do with how the methane and nitrogen molecules are arranged in their crystal structures,” she added.

“Gone is the thought that Pluto is a dead world. New Horizons has picked up evidence that the dwarf planet has been geologically active throughout its four-billion-year life.”

Findings of the study have been published in the journal IUCrJ.


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.

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