A small icy object far beyond Pluto may be surrounded by a very thin atmosphere. During the event, telescopes in Japan recorded a star fading and reappearing gradually rather than disappearing abruptly, which is usually what happens when an airless object passes in front of it. The result, published in Nature Astronomy, points to the possibility of a faint gaseous layer around the distant body 2002 XV93.
Until now, Pluto has been the only object beyond Neptune confirmed to have a stable atmosphere. That’s why any hint of atmospheric activity around a much smaller body like 2002 XV93 stands out immediately in the data coming from these surveys.
A Strange Fading Of A Distant Star
On 10 January 2024, 2002 XV93 passed directly in front of a background star, creating a short occultation observed by a coordinated set of telescopes in Japan. Instead of a clean “on-off” signal in the starlight, the brightness dropped and recovered smoothly over about 1.5 seconds.
That detail matters. In a normal case where an object has no atmosphere, the star’s light should cut out suddenly. Here, the gradual change suggests the light may have been bent or filtered by something surrounding the object.
The team behind the study, reported in Nature Astronomy, describes this pattern as consistent with a very thin layer of gas around 2002 XV93. The observation came from a multi-telescope setup designed specifically to catch these very short events, since they can last only seconds.
Ko Arimatsu from the National Astronomical Observatory of Japan said that he was “genuinely surprised” by what the data showed. The surprise is understandable: the object is only about 470 kilometers wide.
“2002 XV93, has a diameter of approximately 500 km. For reference, Pluto’s diameter is 2,377 km,” the study team explained.
At this scale, the object’s gravity is generally considered too weak to retain an atmosphere over long periods, raising questions about how such a layer could exist at all.
An Atmosphere That Shouldn’t Really Last
If the interpretation is correct, the pressure of this possible atmosphere would be around one ten-millionth of Earth’s. That’s extremely thin, more like a whisper of gas than anything we would normally think of as an atmosphere.
The analysis sticks closely to what the light curve shows: a smooth dimming instead of a sharp cutoff, which is what led researchers to suggest refraction through a gas layer. But the same dataset also makes it clear that this is a single-event detection, not a repeated measurement.
Because of that, there’s still a lot missing. The composition of the possible atmosphere isn’t known, and even its height above the surface can’t be determined from this observation alone.
Gas, Dust, Or Something Temporary
Several scenarios could explain the signal seen during the occultation, but none of them are confirmed yet. One possibility is a recent impact with another icy body, which could have released a short-lived cloud of material around 2002 XV93. Another is ongoing surface activity, such as cryovolcanism, where volatile substances escape from the interior and form a thin surrounding envelope.
But there is also a more cautious option: the signal may not come from gas at all, but from a thin cloud of dust. Such dust could produce a similar effect on starlight, mimicking an atmospheric signature.
“Observations by the NASA/ESA/CSA James Webb Space Telescope show no signs of frozen gases on the surface of 2002 XV93 that might sublimate to form an atmosphere,” the authors noted.
The study is careful about this point, noting that the current observations can’t distinguish clearly between gas and dust.