Giant mountains found on Pluto are believed to be volcanoes that spewed out ice and other volatiles, new research presented on Monday shows.
NASA's New Horizons spacecraft spotted two giant mountains during its unprecedented July 14 flyby of Pluto and its primary moon Charon.
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The mountains are more akin to volcanoes found on Mars and Earth than anything ever previously found in the outer solar system, scientists said during the opening day of the American Astronomical Society's planetary sciences meeting in Maryland.
Pluto's mountains are more than 100 miles across and several miles high. The tops have depressions, similar to volcanic shapes.
"If these are indeed volcanic edifices they would form due to eruption of ice onto the surface of Pluto, rather than eruption of rock. That would be one of the most phenomenal discoveries of New Horizons and it would make Pluto and even more fascinating and unique place than it is already proving itself to be," said planetary scientist Oliver White, with NASA's Ames Research Center in Moffett Field, Calif.
"Whatever they are, they're definitely weird. Volcanoes is probably the least weird hypothesis at the moment," he added.
Heating to fire up the volcanoes likely came from the decay of naturally radioactive elements in its silicate core.
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"The heat source may have died off quite a bit over the 4.5 billion years of Pluto's existence," White said.
"We are dealing with very volatile ices at the surface, if these are indeed cryo-volcanic features, they wouldn't require as much heat to be mobilized and to erupt onto the surface as rock would for the inner terrestrial planets. While there's less heat to go around, perhaps you get more bang for your buck, given the nature of these ices," he said.
Other highlights of some 50 papers being presented by the New Horizons team include details about several large fractures cutting into Pluto's surface, possible evidence of an underground liquid ocean.
Scientists also discovered that Pluto's atmosphere is colder, smaller and more compressed than computer models predicted, and that its four small moons are spinning rapidly and wobbling.
Two of Pluto's moons, Kerberos and Hydra, appear to have two lobes and, like the comet begin studied by Europe's Rosetta spacecraft, may be the result of bodies merging together.
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"This seems to be saying to us that at some point in the past, there were more than just the four moons of Pluto – there were at least six," said New Horizons scientist Mark Showalter, with the SETI Institute in Mountain View, Calif.
The other small moons, Styx and Nix, are extremely elongated objects and could be multi-body objects as well, he added.
Hydra, Pluto's most distant moon, is the system's fastest spinner, rotating every 10 hours. That means it rotates 89 times for each of its 38-day orbits around Pluto.
Scientists expected the moons' rotations would have stabilized over time, but tidal forces from Pluto's large moon Charon are believed to keep the moons' orbits chaotic.
"There's clearly something fundamental about the dynamics of the system that we do not understand," Showalter said. "We expected chaos, but this is pandemonium."