Astronomers have detected what they believe to be a thin, delicate atmosphere surrounding a tiny, icy world beyond Pluto, according to a new study. The object, formally known as (612533) 2002 XV93, is a plutino, meaning it orbits the Sun twice for every three orbits of Neptune. Just 300 miles (500 kilometers) across, it is considered the smallest object in the solar system with a clearly identified global atmosphere held by gravity.
Discovery and Observations
Lead researcher Ko Arimatsu of the National Astronomical Observatory of Japan and his team used three telescopes in Japan to observe the object in 2024 as it passed in front of a background star, briefly dimming the starlight. This technique allowed them to infer the presence of an atmosphere. The findings were published Monday in the journal Nature Astronomy.
“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, lead scientist for NASA’s New Horizons mission to Pluto and beyond. Stern was not involved in the study.
Atmospheric Characteristics
The atmosphere of this cosmic iceball is estimated to be 5 million to 10 million times thinner than Earth’s atmosphere, and 50 to 100 times thinner than Pluto’s tenuous atmosphere. The likely chemical components are methane, nitrogen, or carbon monoxide, any of which could account for the observed dimming.
“It changes our view of small worlds in the solar system, not only beyond Neptune,” Arimatsu said. Finding an atmosphere around such a small object was “genuinely surprising,” he added, challenging the conventional view that atmospheres are limited to large planets, dwarf planets, and some large moons.
Possible Origins and Future Research
The atmosphere may have been created by volcanic eruptions or a comet strike. Further observations, especially by NASA’s Webb Space Telescope, could confirm its composition. “That is why future monitoring is so important,” Arimatsu said. “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.
At the time of the study, the object was more than 3.4 billion miles (5.5 billion kilometers) away, farther than Pluto, which is the only other Kuiper Belt object with a known atmosphere. The finding offers fresh insight into the solar system’s farthest, coldest objects in the Kuiper Belt.
