A new study suggests that a tiny, icy world beyond Pluto harbors a thin, delicate atmosphere that may have been created by volcanic eruptions or a comet strike.
Just 300 miles or so across, this mini Pluto is thought to be the solar system’s smallest object yet with a clearly detected global atmosphere bound by gravity, said lead researcher Ko Arimatsu of the National Astronomical Observatory of Japan.
“This is an amazing development, but it sorely needs independent verification. The implications are profound if verified,” said Southwest Research Institute’s Alan Stern, the lead scientist behind NASA’s New Horizons mission to Pluto and beyond. He was not involved in the study.
If confirmed, the rock would become just the second world past Neptune in our solar system to host an atmosphere — after only Pluto itself.
The finding offers fresh insight into our solar system’s farthest, coldest objects in a region known as the Kuiper Belt. Researchers used three telescopes in Japan to observe the object in 2024 as it passed in front of a background star, briefly dimming the starlight.
“It changes our view of small worlds in the solar system, not only beyond Neptune,” Arimatsu said in an email. Finding an atmosphere around such a small object was “genuinely surprising,” he added, and challenges “the conventional view that atmospheres are limited to large planets, dwarf planets and some large moons.”
Ko Arimatsu/AP 
This so-called minor planet — formally known as (612533) 2002 XV93 — is considered a plutino, circling the sun twice in the time it takes Neptune to complete three solar orbits. At the time of the study, it was more than 3.4 billion miles away, farther than even Pluto, the only other object in the Kuiper Belt with an observed atmosphere.
This cosmic iceball’s atmosphere is believed to be 5 million to 10 million times thinner than Earth’s protective atmosphere, according to the study appearing Monday in the journal Nature Astronomy.
It’s 50 to 100 times thinner than even Pluto’s tenuous atmosphere. The likeliest atmospheric chemicals are methane, nitrogen or carbon monoxide, any of which could reproduce the observed dimming as the object passed before the star, according to Arimatsu.
Further observations, especially by NASA’s Webb Space Telescope, could verify the makeup of the atmosphere, according to Arimatsu.
Ice volcanoes or comet collision?
The researchers could not say for sure what created the atmosphere, which is nowhere near thick enough to support life.
But they suggested it could have been made by gas being shot out from the world’s interior by erupting ice volcanoes.
Or it could have been kicked up by a comet smashing into the world, which would mean it will gradually disappear.
Jose-Luis Ortiz, a Spanish astronomer not involved in the research who studies dwarf planets beyond Neptune, said the results were interesting, but urged caution.
“I still doubt that it is an atmosphere. We need more data,” he told AFP.
An alternative explanation for the observations could be that the object has a ring close to its body, Ortiz said.
Ko Arimatsu acknowledged that he could not rule out “exotic alternatives” to an atmosphere.
However, “a nearly edge-on ring does not seem consistent with the main features of our observations,” he added.
Both astronomers called for further observations to reveal more about this strange world — particularly with the James Webb space telescope.
There have also been suggestions that a dwarf planet called Makemake, which is slightly smaller than Pluto, could have a very thin atmosphere, though some scientists are skeptical. Pluto was long considered our ninth planet, but in 2006 the International Astronomical Union reclassified Pluto as a dwarf planet.
Last week, NASA administrator Jared Isaacman suggested the space agency was considering reinstating Pluto as a fully-fledged planet.
“I am very much in the camp of ‘make Pluto a planet again,'” Isaacman said.
Isaacman made the comments while endorsing a proposal to halve NASA’s science budget, raising concerns among 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 wrote on Bluesky.