Astronomers detect an atmosphere around a tiny frozen world beyond Pluto
Astronomers have confirmed the presence of a thin atmosphere around a small frozen body orbiting the distant reaches of the solar system, overturning long-held assumptions about what small icy worlds are capable of. The object, designated (612533) 2002 XV93, measures approximately 500 kilometers in diameter and lies beyond Neptune. It is now only the second Kuiper Belt object known to possess an atmosphere, after Pluto.
The discovery emerged from a stellar occultation observed on January 10, 2024, when 2002 XV93 passed in front of a distant star as seen from Japan. A team led by Ko Arimatsu of the National Astronomical Observatory of Japan deployed three telescopes across the country to capture the event. Instead of the star's light cutting off abruptly when the object's solid surface blocked it, the brightness faded gradually — a telltale sign of light refracting through a thin gaseous layer. The findings were published in the journal Nature Astronomy.
The atmosphere is extraordinarily tenuous. It is estimated to be between five million and ten million times less dense than Earth's, and between 50 and 100 times thinner than Pluto's already sparse atmosphere. The most likely constituent gases are methane, nitrogen, or carbon monoxide. At roughly 500 kilometers across — compared to Pluto's 2,377-kilometer diameter — 2002 XV93 may be the smallest known object in the solar system to maintain a global atmosphere held in place by gravity. Arimatsu described the detection as "truly unexpected," saying it challenges "the traditional notion that atmospheres are the exclusive domain of large planets, dwarf planets, and some large moons."
The object is classified as a plutino, meaning it shares an orbital resonance with Neptune, completing two full orbits around the Sun for every three Neptune completes, at roughly 40 times the Earth-Sun distance. Computer modeling by the research team indicates that such a fragile atmosphere would disperse within a few hundred to a thousand years, which means some active mechanism must be continuously replenishing it. Two competing explanations have been proposed: a recent cometary impact that released trapped gases from beneath the surface, or active cryovolcanism — ice volcanoes transporting frozen or liquid volatile substances from the object's interior to its surface.
The mystery deepens further because observations from NASA's James Webb Space Telescope have so far found no trace of frozen gases on the surface of 2002 XV93 that could sublimate and sustain an atmosphere. Arimatsu emphasized that continued monitoring will be critical to resolving the question. If the atmosphere dissipates over the coming years, that would support the impact theory. If it remains stable or fluctuates seasonally, it would point toward a steady supply of internal gases from cryovolcanic activity. Either outcome would carry significant implications for understanding the geological and atmospheric potential of small icy bodies throughout the outer solar system.
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