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Far beyond Pluto, where sunlight is faint and temperatures remain extremely low, countless icy bodies drift through the outer reaches of the Solar System. These distant objects, known as trans-Neptunian objects, have long been viewed as frozen relics left over from the Solar System’s formation. Most are thought to be too small to hold onto gases for any significant length of time.For decades, Pluto stood alone as the only known trans-Neptunian object with a confirmed atmosphere. Larger worlds beyond Neptune had been examined, yet astronomers could only place limits on whether any gases surrounded them. That picture has now changed. According to the study published in Nature, titled “Detection of an atmosphere on a trans-Neptunian object beyond Pluto”, observations of a much smaller object called 2002 XV93 have revealed signs of a thin atmosphere, suggesting that even relatively modest icy bodies in the distant Solar System may occasionally develop gaseous envelopes.
How a distant star helped scientists discover an atmosphere beyond Pluto
The discovery emerged from observations made on 10 January 2024, when 2002 XV93 passed in front of a distant star. Such events, known as stellar occultations, allow astronomers to study objects that are otherwise too small and remote to examine in detail.As the object crossed the star’s line of sight, telescopes in Japan recorded subtle changes in the star’s brightness. Instead of the sharp drop expected from a bare solid body, the light curve showed evidence that starlight had been bent before reaching Earth. That bending effect is important because it can occur when light passes through a layer of gas surrounding an object. By analysing the pattern, the research team concluded that the most likely explanation was the presence of a thin atmosphere around 2002 XV93.
Why scientists did not expect a small world like 2002 XV93 to have an atmosphere
What makes the finding unusual is the size of the object itself. The study estimates that 2002 XV93 has a radius of roughly 250 kilometres, making it far smaller than Pluto and many other well-known icy bodies beyond Neptune.As per the study, previous searches for atmospheres around larger trans-Neptunian objects had failed to find convincing evidence, establishing only very low upper limits. Yet this comparatively small body appears to possess a surface pressure between about 100 and 200 nanobars according to the team’s analysis. That is extremely thin by Earth standards, but still substantial for an object of its size and location.The result challenges a long-standing expectation that small worlds in the Kuiper Belt and related populations should struggle to retain volatile gases. Under conventional models, weak gravity and long exposure to space would gradually allow such materials to escape.
Possible origins of the atmosphere on 2002 XV93
The discovery immediately raises a difficult question. If 2002 XV93 is too small to easily hold an atmosphere over long periods. The researchers suggest that the atmosphere may be temporary rather than permanent. One possibility involves cryovolcanism, a process in which icy materials and volatile compounds emerge from the interior instead of molten rock. If internal activity is still occurring, gases could be replenished as older material escapes into space.Another idea points to collisions. The outer Solar System contains countless small icy objects, and an impact could release frozen volatile substances trapped beneath the surface. In that scenario, a recently generated atmosphere might persist for a period before gradually thinning away.At present, the observations do not reveal which explanation is correct. The composition of the atmosphere also remains uncertain, with methane, nitrogen and carbon monoxide among the possibilities considered in the study.
Search for more atmospheric worlds beyond Pluto
Study suggests that Pluto may not be as unusual as once believed. If a body only a few hundred kilometres across can host an atmosphere, other distant icy worlds might be capable of doing the same under the right circumstances.That possibility carries wider implications for understanding the evolution of trans-Neptunian objects. Some may be more active than previously assumed, with internal processes or occasional impacts altering their surfaces and surroundings. Future occultation observations, along with data from advanced observatories, could reveal whether 2002 XV93 is an exception or part of a larger hidden population of atmospheric worlds.For now, the object offers a reminder that the outer Solar System remains full of surprises. Even in regions that appear cold, quiet and unchanged, small frozen worlds may still be capable of producing phenomena once thought reserved for much larger bodies. Go to Source
