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冥王星以外で初めて大気が確認された太陽系外縁天体「２００２ＸＶ９３」の想像図。 A thin atmosphere has been found to exist on one of thousands of trans-Neptunian objects, or TNOs, small celestial bodies outside Neptune, the outermost planet in the solar system, a research team including the National Astronomical Observatory of Japan said.