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Astronomers have detected a faint atmosphere around a small icy body in the outer Solar System, far beyond the orbit of Neptune. The object, designated 2002 XV93, is a Trans-Neptunian Object — a frozen world barely bigger than a large city. Until now, scientists believed that bodies this small could not retain any kind of atmosphere.
The finding, published in Nature Astronomy, suggests that such mini-worlds may be much more active than planetary scientists previously believed. The atmosphere of 2002 XV93 is around five to ten million times thinner than Earth's — so thin that you would not even feel a breeze if you were standing on the surface. So far, the only other Trans-Neptunian Object found with even a hint of an atmosphere is Pluto, which is over five times larger.
The team used a technique known as "occultation". This involves observing how the light of a distant star changes when a planetary body passes in front of it. If the object has no atmosphere, the star's light disappears and reappears sharply. If there is an atmosphere, however, the light is gradually dimmed and brightened — a small but measurable change that the instruments can detect.
The small size of the body means it has a very weak gravitational pull, so any atmosphere around it can easily escape into space. Predictions suggest that the atmosphere may completely disappear within one hundred to one thousand years. This means something must be replenishing the atmosphere — and there are two leading theories about what might be happening.
Trans-Neptunian Object — a small body that orbits beyond Neptune. Occultation — when one celestial body passes in front of another. Gravitational pull — force that attracts objects. Atmosphere — layer of gases around a planet or body. Replenish — to fill up again. Volatile — easily evaporated.
Why is the discovery of an atmosphere on such a small body important for our understanding of the Solar System? What other questions does this discovery raise?
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