In the distant region beyond Neptune, astronomers have discovered a small world with an atmosphere that challenges current understanding. The object, measuring about 500 kilometers (310 miles) across, is too small for its weak gravity to retain an atmosphere for long. Yet it possesses a thin, tenuous atmosphere, Science Alert reports.
This finding on (612533) 2002 XV93 could reshape knowledge about atmospheric retention on small icy bodies in the outer Solar System. The discovery also demonstrates advanced techniques for detecting faint phenomena at great distances.
What is 2002 XV93?
2002 XV93 is a plutino — a small body that shares a similar orbital rhythm with Pluto, orbiting at roughly 40 times Earth's distance from the Sun in resonance with Neptune. These icy worlds serve as a fossil record of the early Solar System, preserving information about its composition and dynamics. The resonance with Neptune indicates that the planet migrated outward in the past.
The Kuiper Belt region beyond Neptune remains difficult to study due to the faintness of these distant, icy objects.
How the Atmosphere Was Detected
In 2024, astronomers led by Ko Arimatsu observed a stellar occultation, when 2002 XV93 passed in front of a distant star. The event was recorded from three locations in Japan.
For a bare rock, the starlight would disappear and reappear abruptly. Instead, the light curve showed gradual dimming for about 1.5 seconds before totality and gradual brightening afterward, lasting a total of 15 to 20 seconds depending on the site. This pattern indicates that starlight was refracted by an atmosphere.
Modeling the Atmosphere
Researchers modeled the atmosphere using Pluto’s as a reference, assuming a temperature structure and composition primarily of methane, nitrogen, or carbon monoxide. They simulated density at different altitudes and light refraction.
The best-fit model points to an extremely thin atmosphere of 100 to 200 nanobars — roughly 5 to 10 million times thinner than Earth’s atmosphere at sea level.
Why This Atmosphere Is Surprising
Such a thin atmosphere should dissipate in just a few hundred to a thousand years. Its current presence implies active replenishment.
Possible explanations include: a recent comet impact that released gases forming a temporary atmosphere, active cryovolcanoes, similar to those suspected on Pluto, releasing volatiles from the interior.
Broader Implications
This is the first detection of an atmosphere on a small trans-Neptunian object (TNO) other than Pluto. The results show that even small bodies can host atmospheres, at least temporarily, and that these can be detected with current technology despite their extreme faintness.
The discovery challenges the traditional view that only larger bodies can sustain significant atmospheres. It suggests that a fraction of distant icy minor planets may exhibit transient atmospheres sustained by cryovolcanic activity or recent impacts.
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