Ko Arimatsu detects Pluto-linked atmosphere on 2002 XV93
Ko Arimatsu led astronomers who detected a thin pluto-linked atmosphere around 2002 XV93, a 500-kilometer object beyond Neptune. The team used a 2024 stellar occultation to pick up light changes that fit refraction through a tenuous atmosphere.
The strongest result points to just 100 to 200 nanobars, or about 5 to 10 million times thinner than Earth's air at sea level. For a body that small, and that far from the Sun, the detection gives astronomers a rare measurement from a class of objects that are difficult to study directly.
Ko Arimatsu in Japan
Arimatsu, the lead astronomer at the National Astronomical Observatory of Japan, observed 2002 XV93 passing in front of a distant star in 2024. The researchers captured the occultation from three different locations in Japan, giving them separate views of the same event.
The occultation lasted 15 to 20 seconds, depending on where it was observed. Around totality, the light curve showed about 1.5 seconds of gradual dimming and brightening before and after the star was fully blocked.
2002 XV93 and Pluto
The object is a plutino, meaning it shares an orbit similar to Pluto's orbital rhythm and stays in resonance with Neptune's orbit. It moves around 40 times Earth's distance from the Sun, where sunlight is weak and small bodies are hard to examine in detail.
That is where the complication comes in: 2002 XV93 measures only around 500 kilometers across, so its weak gravity should not hold an atmosphere for long. The team still found a signal consistent with gas around the body, using refraction models based on Pluto's atmosphere.
Refraction on 2002 XV93
The models assumed a temperature structure and a composition mainly made up of methane, nitrogen, or carbon monoxide. The gradual fading in the light curve matched starlight passing through an atmosphere and bending before reappearing.
For readers following the result, the practical takeaway is narrow but clear: the atmosphere is real enough to register in occultation data, yet so thin that it sits far below Earth's scale. The next step for this kind of work is to use more occultations to test whether 2002 XV93 keeps that air over time or only shows it briefly in this observation.
