Astronomers Detect Atmosphere on Tiny Kuiper Belt World

CAPE CANAVERAL, Fla. Astronomers have detected a thin atmosphere around a small icy object beyond Pluto, marking the solar system's smallest known world with a gravity-bound global atmosphere, according to a new study.

The object, designated 612533 2002 XV93 and classified as a plutino, measures about 300 miles across. Researchers led by Ko Arimatsu of Japan's National Astronomical Observatory observed it in 2024 using three ground-based telescopes. The team captured the object as it passed in front of a distant star, causing a brief dimming of the starlight that revealed the atmosphere's presence. The findings appear in Monday's issue of Nature Astronomy.

At the time of observation, the object was more than 3.4 billion miles from the sun, farther than Pluto and located in the distant Kuiper Belt, a region populated by icy bodies. Its atmosphere is estimated to be 5 million to 10 million times thinner than Earth's and 50 to 100 times less dense than Pluto's tenuous layer, the only other confirmed atmosphere in the Kuiper Belt.

Possible components include methane, nitrogen or carbon monoxide, which could explain the observed dimming effect. Arimatsu noted that the discovery...