Pluto: It's Atmosphere More Extensive Than Thought

Artist’s impression of how the surface of Pluto might look. The image shows patches of pure methane on the surface.

CREDIT: ESO/L. Calçada

A new simulation of Pluto's upper atmosphere shows that it extends so far from the planet that stray molecules may be deposited on its largest moon, Charon.

The new model predicts that Pluto's atmosphere can extend as far as 6,456 miles (10,390 kilometers) into space, or about 4.5 times the diameter of Pluto. That's more than halfway to Charon.

"That is amazing, from my perspective," said Justin Erwin, the lead author of the paper and a Ph.D. student at the University of Virginia.

Researchers combined two previously known models of Pluto's atmosphere to better estimate the escape rate of molecules into space. Their refinement made a big difference.

"Our [calculated escape rate] is a little bit smaller, but the small change in the escape rate causes a large change in the structure of the atmosphere," Erwin added.

Erwin's supervisor at the University of Virginia, Robert Johnson, was a co-author of the paper reporting the findings, which was published on the preprint site Arxiv and has been submitted to the journal Icarus for publication.

Fire and ice
Pluto's tenuous atmosphere is mainly composed of methane, nitrogen and poisonous carbon monoxide that likely comes from ice on the dwarf planet's surface. The size of the atmosphere changes as Pluto moves closer and farther from the sun in its elliptical orbit.

When Pluto swings near the sun, the sun's heat evaporates the ice and gases slowly escape into space. This process continues until Pluto moves away and the sun's heat fades. Then, the ice builds up until Pluto approaches the sun again.

Pluto's last close approach to the sun was in 1989. That is considered a fairly recent event, because it takes 248 years for the dwarf planet to orbit the sun once.

Researchers are trying to refine the escape rate of the gases ahead of the arrival of NASA's New Horizons probe at Pluto in 2015, so that the spacecraft knows what to look for.

For the new calculations, Erwin's team used previously published research from themselves and other scientists.

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