A small, icy world far beyond Neptune is challenging long-standing assumptions about planetary science. Astronomers have discovered evidence of a thin atmosphere surrounding a trans-Neptunian object known as 2002 XV93—an object considered too small and too cold to retain any gaseous envelope.
Located in the outer reaches of the Solar System, trans-Neptunian objects (TNOs) are typically airless due to their weak gravity and extreme temperatures. Only larger bodies like Pluto have been confirmed to host tenuous atmospheres. But 2002 XV93, with a diameter of about 500 kilometers, appears to defy that rule.
The discovery came during a rare alignment event on January 10, 2024, when the object passed in front of a distant star. By analyzing how the starlight gradually dimmed—rather than disappearing abruptly—astronomers identified the signature of a thin atmosphere surrounding the object.
The observations were led by the National Astronomical Observatory of Japan, with contributions from both professional and amateur astronomers across Japan. Their combined data strongly support the presence of an extremely fragile atmosphere.
What makes the finding even more intriguing is its instability. Models suggest that such an atmosphere should dissipate in less than 1,000 years unless it is continuously replenished. However, data from the James Webb Space Telescope show no clear evidence of surface ice that could sustain it through sublimation.
Two main scenarios are being explored. One possibility is that internal processes released volatile materials from beneath the surface. Another is that a recent comet impact injected gas into the surrounding space, temporarily forming an atmosphere.
