An international team of astronomers reported Monday that a frigid, pint-sized world in the outer reaches of the solar system may possess an atmosphere — one so tenuous that it is barely detectable by Earth-based telescopes. If confirmed, the object known as (612533) 2002 XV93 would become the smallest body ever found to retain a global atmosphere by gravity, a distinction that challenges longstanding assumptions about where atmospheres can exist.
The detection relied on a stellar occultation: when the tiny world passed directly in front of a background star in 2024, telescopes in Japan captured a subtle dimming of the starlight, a signature consistent with a diffuse gaseous envelope. “This is an amazing development, but it sorely needs independent verification. The implications are profound if verified,” said Alan Stern of the Southwest Research Institute, the lead scientist behind NASA’s New Horizons mission to Pluto and beyond, who was not involved in the study.
Lead researcher Ko Arimatsu called the finding “genuinely surprising,” noting that it challenges “the conventional view that atmospheres are limited to large planets, dwarf planets and some large moons.” The object, formally classified as a plutino, orbits the sun twice for every three orbits of Neptune and was more than 3.4 billion miles from Earth at the time of the observations — farther than Pluto itself.
The suspected atmosphere is extraordinarily thin. The study estimates it is 5 million to 10 million times less dense than Earth’s protective blanket, and 50 to 100 times thinner than even Pluto’s wispy atmosphere. According to Arimatsu, the likeliest chemical constituents are methane, nitrogen or carbon monoxide, any of which could reproduce the observed starlight dimming.
The origin of the atmosphere remains an open question. Arimatsu said that if the gas envelope is produced by ongoing volcanic activity — cryovolcanoes spewing ice and volatile compounds from the interior — it may persist or vary with the object’s seasons. Alternatively, a comet strike could have blasted material off the surface to create a temporary, fading atmosphere. “That is why future monitoring is so important,” he said. “If the atmosphere fades over the next several years, that would support an impact origin. If it persists, or varies seasonally, that would point more toward ongoing internal gas supply.”
Further observations, especially by NASA’s James Webb Space Telescope, could verify the atmosphere’s composition and monitor its evolution. The study appears in the journal Nature Astronomy.