A team of astronomers in Japan has detected a thin atmosphere around (612533) 2002 XV93, a trans-Neptunian object about 500 km in diameter — an object far too small and cold to retain one.
An artist’s conception of the trans-Neptunian object 2002 XV93. Image credit: NAOJ.
“In the cold reaches of the outer Solar System lie thousands of small objects known as trans-Neptunian objects (TNOs) because they lie outside the orbit of Neptune,” said Dr. Ko Arimatsu from Ishigakijima Astronomical Observatory and colleagues.
“A thin atmosphere has been observed around Pluto, the most famous TNO, but studies of other TNOs have yielded negative results.”
“Most TNOs are so cold, and their surface gravity so weak, that they are not expected to retain atmospheres.”
The astronomers observed the trans-Neptunian object 2002 XV93 using a stellar occultation, measuring how it briefly dimmed the light of a background star as it passed in front of it.
“2002 XV93, has a diameter of approximately 500 km. For reference, Pluto’s diameter is 2,377 km,” they explained.
“The orbit of 2002 XV93 is such that, as seen from Earth, it passed directly in front of a star on January 10, 2024.”
“As the star disappears behind 2002 XV93, it might gradually fade, indicating that the light is being attenuated as it passes through a thin atmosphere; or it might suddenly wink out as it slips behind the solid surface of the TNO.”
The researchers found that the observations are best explained by a thin atmosphere surrounding 2002 XV93.
Their calculations indicate that such an atmosphere would dissipate in less than 1,000 years unless it is somehow replenished.
That means it must have formed — or been replenished — relatively recently.
“Observations by the NASA/ESA/CSA James Webb Space Telescope show no signs of frozen gases on the surface of 2002 XV93 that might sublimate to form an atmosphere,” the authors said.
“One possibility is that some event brought frozen or liquid gases from deep inside the TNO to the surface.”
“Another possibility is that a comet crashed into 2002 XV93, releasing gas that formed a temporary atmosphere.”
“Further observations are needed to distinguish between these two scenarios.”
“This discovery shows that even a few-hundred-kilometer TNO can host, at least transiently, an atmosphere, challenging standard volatile-retention scenarios,” they concluded.
“Our findings suggest that a fraction of distant icy minor planets can exhibit atmospheres, potentially sustained by ongoing cryovolcanic activity or produced by a recent impact of a small icy object.”
The team’s paper was published in the journal Nature Astronomy.
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K. Arimatsu et al. Detection of an atmosphere on a trans-Neptunian object beyond Pluto. Nat Astron, published online May 4, 2026; doi: 10.1038/s41550-026-02846-1
