Posted on by

We may have found our very first exomoon, opening a new chapter in space exploration

We may have found our very first exomoon, opening a new chapter in space exploration

  • Scientists believe they have gathered convincing evidence of the presence of an exomoon – a moon orbiting a planet outside our solar system.
  • By analyzing the movements of a mysterious sodium cloud moving around the planet WASP-49 b, the team was able to construct a convincing argument for the presence of an exomoon.
  • Although many candidates have been proposed, there has never been any confirmed evidence of an exomoon.

Moons probably don’t only exist in our solar system. That’s probably not the case for most things (including life, but that’s another discussion). But despite the many distant stars and exoplanets we have found at this point in our space exploration history, we have yet to find a definitive exomoon – a moon located anywhere other than our small star system.

We’ve definitely found candidates, but we still need to confirm something – partly because multiple candidates become less likely with more data, and partly because it’s really difficult to detect exomoons. In general, they are faint, small, and block less light from stars for shorter periods of time than planets. That is, a new study was published in The astrophysical diary letters May have brought us one step closer than ever to discovering a natural satellite on another world in a very different system.

The secret? Sodium.

The team behind this new study — led by Caltech researcher Apurva Oza — has focused some of our best observing equipment on a mysterious sodium cloud floating around the planet WASP-49 b (which itself orbits the star WASP 49). This cloud was first discovered in 2017 and Oza has been studying it ever since in the hope that it indicates a volcanic exomoon.

See, from what you hear, the sodium shouldn’t be there. WASP-49 b (a hot, Saturn-like planet) and the star it orbits are both composed primarily of hydrogen and helium. The trace amounts of sodium they have could in no way sustain this cloud, which appears to be actively renewing itself at a rate of 220,000 pounds of sodium per second. But still it is there.

So the team looked around and they managed to find several pieces of evidence that seem to point pretty convincingly in the exomoon direction. For one thing, the cloud appeared to double in size, as if it was being refueled, even though it wasn’t directly next to the planet at the time. And on the other hand, the cloud is moving in the wrong direction for it to be a planetary atmospheric phenomenon. “We believe this is a truly crucial piece of evidence,” Oza said in a news release. “The cloud is moving in the opposite direction that physics would tell us if it were part of the planet’s atmosphere.”

In addition to their observations, the team ran modeling to understand the behavior of this cloud. Ultimately, they found that the seemingly irregular movements in front of, behind, and around WASP-49 and WASP-49 b, as well as the apparent lack of connection to a specific location on the surface of WASP-49 b, were best compounded by the presence of a moon an eight-hour orbit around the planet.

These already exciting data points are compounded by the fact that we’ve actually seen a moon in our own cosmic backyard behave in pretty much this way. Jupiter’s moon Io is the most volcanic object in our solar system and is powered by the constant push-and-pull deformations of tidal forces exerted on it by its planetary host. It ejects so much gas and debris that, according to NASA, it could create clouds around Jupiter that are up to 1,000 times the radius of the planet itself. If this potential exomoon is anything like Io, it’s certainly within the realm of possibility , that it would create a sodium cloud that we could see long before we could directly detect the planet.

The possible existence of this moon is exciting, but if we want to confirm its presence we must act quickly. (Well, fast on a cosmic scale anyway). The tidal forces required to generate the amount of volcanic activity required to form such a sodium cloud are extremely powerful and likely take a significant toll on the Moon’s structural integrity. Furthermore, if you throw a bunch of the stuff you’re made of out into the universe via large volcanoes, you no longer have that stuff in you, which makes you even weaker. If we are right about the nature of this object, over time it will essentially decay into nothing more than debris around a distant star. “If there really is a moon there,” Oza said, “it will have a very destructive end.”

It’s good that our telescopes are getting better and better. At some point, there’s a good chance we’ll know exactly what makes up that cloud. Until then, we’ll just have to be patient with promising evidence.

Jackie is a writer and editor from Pennsylvania. She particularly enjoys writing about space and physics and loves sharing the strange wonders of the universe with anyone who will listen. She is looked after by her two cats in her home office.