Study Detects Thin Atmosphere on Tiny Kuiper Belt Object Beyond Pluto

A new study indicates that a small icy world beyond Pluto has a thin atmosphere possibly produced by volcanic activity or a comet impact.

The object, about 300 miles across, represents the smallest body in the solar system with a clearly detected gravity-bound global atmosphere, according to lead researcher Ko Arimatsu of Japan's National Astronomical Observatory.

"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, principal investigator for NASA's New Horizons mission to Pluto. Stern did not participate in the study.

Confirmation would make this the second object past Neptune with an atmosphere, following only Pluto.

The discovery provides new information on the solar system's most distant and coldest bodies in the Kuiper Belt. In 2024, researchers observed the object occulting a background star with three telescopes in Japan, causing a brief dimming of the starlight.

"It changes our view of small worlds in the solar system, not only beyond Neptune," Arimatsu said in an email. He called the presence of an atmosphere on such a small body "genuinely surprising" and said it challenges "the conventional view that atmospheres are limited to large planets, dwarf planets and some large moons."

Designated (612533) 2002 XV93, the object is a plutino that orbits the sun twice for every three orbits Neptune completes. During the observations, it sat more than 3.4 billion miles from Earth, farther than Pluto, the only other Kuiper Belt object with a confirmed atmosphere.

The study's atmosphere is estimated at 5 million to 10 million times thinner than Earth's. It is 50 to 100 times thinner than Pluto's atmosphere. Likely components include methane, nitrogen or carbon monoxide, which match the observed dimming, Arimatsu said.

NASA's James Webb Space Telescope could analyze the atmosphere's composition in future observations, Arimatsu noted.

Researchers could not determine the atmosphere's origin, which is far too sparse to sustain life. They proposed ice volcanoes ejecting gas from the interior or a comet collision stirring up material, which would cause the atmosphere to dissipate over time.

Jose-Luis Ortiz, a Spanish astronomer who studies trans-Neptunian dwarf planets but was not involved, called the results interesting but advised caution. "I still doubt that it is an atmosphere. We need more data," he told AFP.

Ortiz suggested a close-in ring system as an alternative explanation for the dimming.

Arimatsu said he could not exclude "exotic alternatives" to an atmosphere but added that "a nearly edge-on ring does not seem consistent with the main features of our observations."

Both astronomers recommended more observations, especially with the James Webb Space Telescope.

Makemake, a dwarf planet slightly smaller than Pluto, may also have a very thin atmosphere, though some researchers question this. The International Astronomical Union reclassified Pluto as a dwarf planet in 2006 after previously recognizing it as the ninth planet.

Last week, NASA administrator Jared Isaacman voiced support for restoring Pluto's planet status. "I am very much in the camp of 'make Pluto a planet again,'" he said while backing a plan to cut NASA's science budget in half, which upset some astronomers.

"It's wild to 'make Pluto a planet again' while decimating the careers of those of us that study it!" planetary scientist Adeene Denton posted on Bluesky.