This Small Celestial Object Beyond Pluto Shouldn’t Possess an Atmosphere—but Astronomers Indicate They Might Have Sensed One
Celestial bodies of this size and distance are generally believed to be too frigid and possess insufficient surface gravity to retain gases. However, the results indicate that icy, rocky entities in the far reaches of our solar system exhibit greater dynamism than previously assumed.
Illustration depicting a temporal sequence as the cosmic object traverses in front of a remote star
NAOJ
A small, icy celestial object located beyond Pluto appears to possess something unexpected: an atmosphere. Scientists are not inclined to anticipate that such a tiny, distant world can retain gases. Therefore, the discoveries described in a study released on May 4 in the journal Nature Astronomy challenge conventional beliefs regarding these space entities.
“This finding implies that small icy worlds past Neptune may be more active or dynamic than we commonly presumed,” remarks study co-author Ko Arimatsu, an astronomer at the National Astronomical Observatory of Japan, to Science News’ Lisa Grossman.
The celestial object in focus is known as 2002 XV93. It’s among the many trans-Neptunian objects (TNOs) orbiting the sun within the Kuiper Belt, which is populated with rocks and ice. The dwarf planet Pluto is perhaps the most renowned TNO, being the sole one confirmed to have an atmosphere. However, the majority of these entities are believed to be excessively cold and possess such low surface gravity that they shouldn’t be able to sustain a gas layer.
Interesting fact: A mini Pluto?
2002 XV93 is officially categorized as a “plutino,” a variety of TNO that completes two orbits around the sun in the time it takes Neptune to make three.
Nevertheless, Arimatsu and his team—including amateur astronomers—examined the possibility of 2002 XV93 having a hidden atmosphere. They capitalized on an astronomical event occurring on January 10, 2024, when 2002 XV93 moved directly in front of a distant star from Earth’s viewpoint, with instruments at three locations in Japan capturing data during the eclipse.
The manner in which the icy, rocky object obscured the star’s light provided clues about its gas envelope. A sudden disappearance followed by reappearance of the glow would indicate a lack of atmosphere. Conversely, a gradual fading would suggest the presence of one. To their astonishment, researchers observed the latter.
“The observational data revealed a smooth transition in the star’s brightness near the shadow’s edge, lasting approximately 1.5 seconds,” Arimatsu informs CNN’s Ashley Strickland. “Such a smooth brightness fluctuation can be naturally explained if the starlight was refracted by a very delicate atmosphere surrounding the object.”
This atmosphere likely differs significantly from that of Earth. The researchers estimated that 2002 XV93’s possible atmosphere is around 5 million to 10 million times less dense than Earth’s.
“You wouldn’t be able to breathe it, sense any wind from it, or see anything akin to Earth’s sky,” Arimatsu explains to New Scientist’s James Woodford. “Yet, scientifically, it isn’t trivial, as even such a tenuous atmosphere can noticeably refract starlight, and it indicates the presence or supply of volatile gases around a very small icy entity.”
Conceptual animation for Arimatsu et al. (2026)
Additionally, the team updated 2002 XV93’s presumed diameter to around 292 miles. In comparison, Pluto measures 1,477 miles across. Given the small size of 2002 XV93 and its resultant weak gravity, the team anticipates its atmosphere to last less than 1,000 years unless it is replenished. They also speculate that it could have been formed or refreshed recently.
But how?
Recent data from the James Webb Space Telescope has not shown any signs of frozen gases on the surface that could sublimate to generate an atmosphere. It could be that icy volcanoes have vented gases from deep within 2002 XV93, or perhaps an icy asteroid struck it and released gases, the researchers propose.
“If the atmosphere originated from an impact, its presence may diminish over the forthcoming years or decades. Should it remain stable or exhibit seasonal changes, that would favor a sustained internal supply,” Arimatsu relays to Reuters’ Will Dunham.
Nonetheless, researchers need to collect further observations, especially to validate the study’s conclusions.
“This is an extraordinary finding, but it urgently requires independent confirmation,” Alan Stern, a planetary scientist at the Southwest Research Institute who was not involved in the study, informs the Associated Press’ Marcia Dunn. “The ramifications are significant if confirmed.”