Scientists have discovered a small icy object beyond Neptune that has its own thin atmosphere, a finding that challenges long-held assumptions about distant worlds in the solar system.
The object, officially named (612533) 2002 XV93 but nicknamed a "mini-Pluto," measures just 500km across, making it far smaller than Pluto’s 2,370km diameter.
Despite its size, researchers have detected a global atmosphere held in place by gravity, the first time such an atmosphere has been observed on a body this small beyond Neptune.
Until now, Pluto was the only known celestial body beyond Neptune with an atmosphere.
The atmosphere is between five and 10 million times thinner than Earth’s and its composition is not yet confirmed.
Scientists believe it could be made up of methane, nitrogen or carbon monoxide, according to findings published on Monday in Nature Astronomy.
"It was generally thought that an atmosphere would not exist on such a small object," said co-author Junichi Watanabe, director of the Koyama Space Science Institute at Kyoto Sangyo University.
"This suggests that even in a distant, cold world, there are dynamisms we haven’t imagined," Watanabe added.
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Lead author Prof Ko Arimatsu, head of the Ishigakijima Astronomical Observatory, said the discovery "changes our view of small worlds in the solar system, not only beyond Neptune."
He described finding an atmosphere around such a small body as "genuinely surprising" and said it undermines the conventional view that atmospheres are limited to large planets, dwarf planets and big moons.
The atmosphere could be long-lasting, sustained by cryovolcanism, a cold form of volcanism in which volatile gases seep through cracks in the icy surface.
This, scientists revealed, would differ from Earth’s volcanoes, involving ice and gas rather than molten rock.
Alternatively, the atmosphere might be temporary, created by gases released after a recent impact from a smaller object.
If that is the case, it could fade within years or decades, and if it persists or changes with the seasons, that would point to an ongoing internal source.
"This discovery suggests that some small icy bodies in the outer solar system may not be completely inactive or unchanging, as previously assumed," Arimatsu said.
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