Astronomers May Have Just Discovered A Bizarre Moon Unlike Any We Know

No one has ever confidently detected a moon outside of our solar system, but a team of astronomers led by Kevin Hoy might have just found the first one. The object orbits a brown dwarf in the CD-35 2722 system, about 73 light-years from Earth, and the findings were published in Nature back in July 2026.

Alice Zurlo, one of the astronomers who worked on the study, called it "the first plausible detection of an exosatellite." But, this celestial body isn't anything like the small, rocky moons in our own solar system. Instead, it appears to be a massive, gaseous body. In fact, the researchers note that the object is so massive it could be a planet. However, because it doesn't orbit a star specifically, its classification remains disputed.

Of course, studying far off objects like this is a lot more difficult than studying those closer to us. The moon that orbits Earth, for example, is much easier to study, as we can actually send physical spacecraft to it in a timely manner. This has allowed us to gather soil samples, which could even help researchers find something that could help humans live on the moon. With objects like the one in CD-35 2722, though, researchers have to work with data that can be a lot more ambiguous.

The researchers weren't able to actually see the object itself, so they watched the brown dwarf instead, looking for a small wobble in its light that would show something was pulling on it with its gravity. Astronomers call this the radial velocity method, and it's the same technique that was used to find the very first exoplanet orbiting a star like our sun.

The researchers used the CRIRES+ instrument on the ESO's Very Large Telescope to observe the brown dwarf on and off from October 2023 through February 2026, allowing them to capture 23 usable measurements. When they lined all of those up, the brown dwarf's wobble repeated itself about every 170 days. Based on that signal, the object would be orbiting around 0.2 astronomical units from the brown dwarf, with a minimum mass of about 0.9 times that of Jupiter.

The brown dwarf sits about 60 times farther from its star than Earth does from the sun, so there wasn't much starlight getting mixed into the light the researchers were measuring. That has been an issue in the past when astronomers have tried this with objects that sit closer to their stars, and none of those earlier attempts led to a confirmed signal.

Brown dwarfs already sit somewhere between planets and stars, as they're too massive to be planets, but they don't have enough mass to sustain hydrogen fusion in their cores like a star. The one in CD-35 2722 has about 37 times the mass of Jupiter. Brown dwarfs can look a lot like giant planets in other ways, too. Astronomers have found Earth-like water and weather outside our solar system on one called WISE 0855, where clouds get thicker and thinner as it spins.

Because it orbits a brown dwarf instead of a planet, astronomers don't agree on what it should be called. There's no official definition of an exomoon, and the International Astronomical Union's rules allow planets to orbit brown dwarfs, so the object arguably counts as a planet. Roman Rafikov, a Cambridge astronomer who wasn't involved in the study, went even further, saying "I would definitely not call it an exomoon or exosatellite." However, for now, the team is using exosatellite, the broader term for any satellite outside our solar system.

Confirming any moon outside our solar system has been difficult, though. In 2017, astronomers thought the first "exomoon" may have been spotted, but that candidate and the others found since then still lack confirmation. The team behind this new detection also tested a model with two satellites orbiting the brown dwarf, but a setup like that would likely fling itself apart after a few hundred years. More observations are still needed to confirm what is actually pulling on the brown dwarf. If the object does turn out to be real, Hoy says it's "definitely possible" that it could have moons of its own, as long as they're on tight orbits so gravitational tides can't pull them away.