Astronomers looking for the unexpected find atmosphere

I read a lot of papers and press releases for this show, and it’s rare any more that a particular turn of phrase catches my attention. The good folks at the National Astronomical Observatory of Japan, however, said something so right I had to write it down.

Quote: “But astronomers like to expect the unexpected.”

This was stated in the context of astronomers, who knew full well that a small world statistically shouldn’t have an atmosphere and nevertheless going looking. And you know what, that “The cases that could cause an atmosphere are so few we can’t expect to see one” world has an atmosphere.

https://youtu.be/pHgoRPLFopI?si=fwyEmJxhjKeYlW_X

Yup, we like to do things like point telescopes at the emptiest place on the sky to see what is there if we just look hard enough. We like to go to the bottoms of mines and check if life can be found in the sunless soil. We like to look in places where science isn’t expected and see what we can see. This is how we know the sky is full of galaxies, our world, even kilometers down, is full of life, and … we know that “shouldn’t have an atmosphere world has an atmosphere.

We are the finders of the improbable.

That world, 2002 XV93, is about 500km across, or less than ¼ the diameter of Pluto. With not a lot of mass, and a whole lot of cold, any atmosphere it has can only be temporary as time will cause it to either freeze to the world’s surface or drift away.

But, this is not an impossible situation. We see centaurs — rocky / icy worlds in closer to toward Jupiter or Saturn, sometimes grow temporary atmospheres as they become what we call active. That is a fancy phrase for — “Energy got released and cause ice to become gas”. We think things like landslides, where gravitational potential energy becomes kinetic energy, may be one possibility. Collisions between objects can also release energy.

And these same kinds of things could have happened on the much larger and further out 2002 XV93.

Given the distance to this world, and our utter lack of plans to build a spacecraft headed out that way, it is unlikely that we’ll know exactly what happened anytime in the next couple of decades, but someday, this improbable situation will become a fun “So, this one time,” kind of a story.

To be an astronomer, the path is simple: channel your inner White Witch and believe “as many as six impossible things before breakfast.” And then look for proof.

Sources

• NAOJ Press Release
• Ko Arimatsu et al. “Detection of an atmosphere on a trans-Neptunian object beyond Pluto”, in Nature Astronomy, DOI: 10.1038/s41550–026–02846–1

This content was originally written for the EVSN podcast. Watch video episodes and check out additional content at EVSN.tv.