A tiny icy object beyond Pluto may have a global atmosphere, researchers report
A new study suggests a tiny icy world beyond Pluto has a thin, delicate atmosphere that remains bound by gravity, challenging what scientists previously assumed about which objects can sustain atmospheres in the outer solar system. The object, formally known as (612533) 2002 XV93, measures about 300 miles (500 kilometers) across, according to the researchers.
The discovery focuses on the Kuiper Belt region, where icy bodies orbit far from the sun. In the 2024 observations described in the study, researchers used three telescopes in Japan to watch the object pass in front of a background star, a method that briefly dims starlight when material around the object absorbs or scatters the light.
Lead researcher Ko Arimatsu of the National Astronomical Observatory of Japan said the team detected a clearly observed global atmosphere around such a small body. In an email, Arimatsu said the result “changes our view of small worlds in the solar system, not only beyond Neptune,” and he added that finding an atmosphere on the object was “genuinely surprising.”
The study estimates that the atmosphere is far thinner than Earth’s. It said the atmosphere is 5 million to 10 million times thinner than Earth’s protective atmosphere, and it described the atmosphere as far thinner than even Pluto’s tenuous atmosphere, by a factor of about 50 to 100.
Researchers said the atmospheric chemicals most likely to reproduce the observed starlight dimming are methane, nitrogen or carbon monoxide. They also said further monitoring could help clarify where the gas comes from—whether it reflects internal activity or the aftermath of an impact event.
Arimatsu said that future observations, “especially by NASA’s Webb Space Telescope,” could verify the atmosphere’s makeup. He also said the pattern of how the atmosphere changes over time could provide clues to its origin, adding, “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” from ice volcanoes.
Alan Stern, who led NASA’s New Horizons mission to Pluto and beyond and serves as the lead scientist for the mission, said the discovery was promising but required independent confirmation. Stern said, “This is an amazing development, but it sorely needs independent verification. The implications are profound if verified,” and Stern said he was not involved in the study.
The findings were published Monday in the journal Nature Astronomy. At the time of the study observations, (612533) 2002 XV93 was more than 3.4 billion miles (5.5 billion kilometers) away, farther than even Pluto, the only other Kuiper Belt object with an atmosphere that has previously been observed, according to the report.