A team of astronomers in Japan has discovered evidence of a faint atmosphere surrounding the small trans-Neptunian object 2002 XV93. Previously, only Pluto was known to retain an atmosphere among bodies beyond Neptune due to its stronger gravity. The finding, made via a rare stellar occultation on January 10, 2024 and published in Nature Astronomy, indicates a short-lived atmosphere requiring continuous replenishment.
Astronomers led by Ko Arimatsu at NAOJ Ishigakijima Astronomical Observatory observed 2002 XV93—a trans-Neptunian object about 500 km across—passing in front of a background star on January 10, 2024. Viewed from multiple locations in Japan, the event produced a gradual dimming of starlight consistent with refraction through a thin layer of gas.
This stellar occultation revealed an unexpected atmosphere on an object far smaller than Pluto (2,377 km across), which has a confirmed thin atmosphere. Among thousands of icy trans-Neptunian objects beyond Neptune's orbit, low temperatures and weak gravity typically prevent gas retention.
The research, published in Nature Astronomy and reported by The Japan Times on May 5, 2026, suggests the atmosphere would dissipate in less than 1,000 years without replenishment, implying recent formation or renewal. James Webb Space Telescope data shows no frozen gases on the surface to sublimate, leading scientists to consider alternatives like internal material exposure or comet impacts.
Further observations are needed to determine the atmosphere's composition and origin. The team includes Fumi Yoshida, Tsutomu Hayamizu, Satoshi Takita, Katsumasa Hosoi, Takafumi Ootsubo, and Jun-ichi Watanabe.
The discovery expands understanding of trans-Neptunian objects, suggesting distant small bodies may retain atmospheres more commonly than previously thought.