Atmosphere detected on a small trans-Neptunian object beyond Pluto

Imagine something so small and so distant that its existence seems almost irrelevant, but which suddenly calls into question everything we thought we knew about the Solar System: an icy object the size of a city, orbiting beyond Pluto, has just been shown to have an atmosphere. Until now, an atmosphere was a luxury reserved for planets and, at most, for Pluto, but this discovery forces us to rethink the rules. Most of us think that only large celestial bodies can hold gases around them: the gravity of smaller bodies would be too weak, the cold of space would freeze everything, and any atmosphere would dissipate in an instant. However, the discovery of an atmosphere on the trans-Neptunian object 2002 XV93, which is just 310 miles in diameter, proves that we were wrong. Not only is it possible, but it's happening right where we least expected it. The protagonist of this story is Ko Arimatsu, a Japanese astronomer who, together with an international team and the help of amateurs, decided to closely monitor the occultation of a star by this small TNO. What they observed was subtle but revolutionary: the star did not suddenly go dark as it passed behind the object; instead, its light gradually dimmed, as if passing through a thin haze. That could only mean one thing: there was an atmosphere. And not just any atmosphere, but one with a pressure of between 100 and 200 nanobars—higher than had been observed in objects of this size, and even exceeding the theoretical limits for larger bodies like Makemake, which had already surprised scientists with its methane emissions. Imagine the effort: accurately predicting the time of the occultation, coordinating professional and portable telescopes at various locations around the world, and relying on perfect conditions for just a few seconds. On the night of January 10, 2024, only three locations in the world managed to capture the event, and most of the key data came from telescopes operated by amateurs—ordinary people with modest equipment but enormous passion. Without them, the atmosphere of 2002 XV93 might have gone completely unnoticed. What makes everyone ponder is that this object is about 40 times farther from the Sun than Earth, in a region where nothing like this was supposed to exist. And there's even more: no one knows for sure how it manages to maintain that atmosphere. Could it be active cryovolcanism, releasing gases from its interior? Or could it have been a recent collision with another icy body? The only thing that is certain is that we now need to look at all the small worlds in the Solar System with fresh eyes, because they may hold atmospheric secrets we can't even imagine. There is one angle that the excitement surrounding the discovery might overlook: If such an unexpected atmosphere could only be detected thanks to coordination between professionals and amateurs, how many other phenomena are we missing out on simply because there aren't enough eyes looking at the right time? The universe could be teeming with fleeting atmospheres that cross the threshold of possibility for just a few days or weeks, and no one sees them. In the end, atmospheres aren't the domain of the big players; it's a matter of being in the right place at the right time, and of never underestimating the small details of the cosmos. If an icy rock 6 billion kilometers away can have an atmosphere, the line between planets and “mere rocks” becomes much more blurred than we thought. If this story has made you look at the small worlds of the Solar System in a different light, you can mark it with I'm In in Lara Notes: it's not just about saving the idea; it's about making it your own, because now it belongs to you. And if you end up talking about this with someone—over dinner, in class, or with your kids—you can use Shared Offline to document that special conversation, exclusively in Lara Notes. This discovery comes from The Conversation and saves you 12 minutes of reading.