Far beyond Neptune, in one of the coldest and darkest regions of our solar system, astronomers have discovered something unexpected: a small icy object with an atmosphere that shouldn’t really be there.
This object, known as 2002 XV93, belongs to a group of distant bodies called trans-Neptunian objects (TNOs).
These objects orbit the Sun at vast distances and are usually very cold, with weak gravity.
Because of this, scientists generally believe that most TNOs cannot hold onto an atmosphere. Even Pluto, the most famous TNO, has only a very thin atmosphere.
But 2002 XV93 has surprised scientists. It is much smaller than Pluto, with a diameter of about 500 kilometers compared to Pluto’s 2,377 kilometers.
Based on its size and conditions, it should not be able to keep any gas around it. Yet new observations suggest that it does.
The discovery was made by a team of professional and amateur astronomers in Japan. They took advantage of a rare event on January 10, 2024, when 2002 XV93 passed directly in front of a distant star, as seen from Earth.
This kind of event is called an occultation. By carefully watching how the star’s light changed as the object moved in front of it, scientists could learn more about the object itself.
If 2002 XV93 had no atmosphere, the star’s light would suddenly disappear as the object blocked it. But instead, the light faded gradually. This is a key sign that the light passed through a thin layer of gas before being blocked, suggesting the presence of an atmosphere.
The findings were reported by a team led by Ko Arimatsu at the NAOJ Ishigakijima Astronomical Observatory and published in Nature Astronomy. Their results indicate that the atmosphere around 2002 XV93 is extremely thin and likely temporary.
In fact, calculations suggest that this atmosphere could only last for less than 1,000 years unless it is constantly being replenished. That raises an important question: where did it come from?
Observations from the James Webb Space Telescope show no clear signs of frozen gases on the surface that could turn into gas and form an atmosphere. This makes the mystery even deeper.
Scientists have proposed a couple of possible explanations. One idea is that gases from deep inside the object somehow reached the surface and escaped into space, forming a temporary atmosphere. Another possibility is that a recent comet impact released gas, creating a short-lived atmosphere.
For now, no one knows for sure. Future observations will be needed to solve this puzzle. What is clear, however, is that even the smallest and most distant worlds in our solar system can still surprise us.
