"Finding an atmosphere around such a small object was genuinely surprising."
— Lead researcher Ko Arimatsu
A Tiny World in the Kuiper Belt Has a Surprising Atmosphere
The Discovery
A new study published in Nature Astronomy has detected a global atmosphere around (612533) 2002 XV93, a minor planet known as a plutino in the Kuiper Belt.
At roughly 300 miles (500 km) across, it is the smallest solar system body ever confirmed to have a gravity-bound global atmosphere. This challenges the long-held assumption that only large planets, dwarf planets, and major moons can hold onto such a gaseous envelope.
Key Details of the Atmosphere
- Extreme Thinness: The atmosphere is estimated to be 5 million to 10 million times thinner than Earth’s, and 50 to 100 times thinner than Pluto’s.
- Detection Method: The finding was made in 2024 using three telescopes in Japan. Astronomers observed the object as it passed in front of a background star—an event known as an occultation—causing a brief, measurable dimming of the starlight.
- Likely Composition: The researchers suggest the atmosphere likely contains methane, nitrogen, or carbon monoxide.
- Distant Location: At the time of the study, the object was more than 3.4 billion miles (5.5 billion km) from Earth—farther than Pluto.
- Orbital Classification: (612533) 2002 XV93 is a plutino, meaning it orbits the Sun twice for every three orbits of Neptune.
Skepticism and Alternative Explanations
While the finding has excited the astronomical community, it has also drawn caution.
Astronomer Jose-Luis Ortiz, who was not involved in the study, expressed doubt, suggesting that a near-edge-on ring of debris could explain the observed dimming rather than an atmosphere. Lead researcher Ko Arimatsu acknowledged that such "exotic alternatives" cannot be completely ruled out, but noted that a nearly edge-on ring does not appear consistent with the main features of the observations.
Alan Stern of the Southwest Research Institute, lead scientist of NASA’s New Horizons mission, called the finding "amazing" but stressed the need for independent verification.
How Did It Get an Atmosphere?
The researchers propose two possible origins:
- Outgassing from the interior via cryovolcanic eruptions (ice volcanoes), which would provide a steady, ongoing supply of gas.
- A temporary atmosphere created by a comet impact, which would gradually dissipate into space over time.
Future monitoring could distinguish between these scenarios. If the atmosphere fades over several years, it would support the impact origin. If it persists or shows seasonal variations, it would point toward ongoing internal activity from cryovolcanism.
Why It Matters
If confirmed, this would be only the second world beyond Neptune known to host an atmosphere, after Pluto. The discovery directly challenges the conventional view that stable atmospheres are limited to larger celestial bodies.
Separately, there have been suggestions that the dwarf planet Makemake may also have a very thin atmosphere, though some scientists remain skeptical.
The Next Steps
Both Arimatsu and Ortiz agree on one thing: additional observations are critical.
Further studies, particularly from NASA’s Webb Space Telescope, could verify the atmosphere’s exact composition and help settle the debate over its origin.