The first potential exomoon has arrived, and it makes our Moon appear comically small.

      Scientists might have discovered the first exomoon, although this particular one is as large as Jupiter.

      This artistic depiction illustrates a potential volcanic moon located between the exoplanet WASP-49 b and its star. New findings suggesting that a significant sodium cloud observed near WASP-49 b does not originate from either the planet or the star have led researchers to speculate whether the source could be an exomoon.

      We have already identified over 6,000 planets beyond our immediate vicinity. However, locating a moon orbiting one of these distant planets has proven much more challenging. Astronomers might finally be on the verge of a significant finding, but this object stretches the definition of "moon" significantly.

      Utilizing the Very Large Telescope in Chile, scientists detected strong indications of a moon-like entity within the CD-35 2722 system. Further observations are needed to validate this discovery, but it has the potential to be the first confidently confirmed natural satellite beyond our solar system. There is, however, a small complication: this moon appears to be quite massive.

      Labeling this object as a moon is complicated.

      The existence of a second exomoon candidate suggests that exomoons could be as prevalent as exoplanets. The CD-35 2722 system is radically different from our own. It consists of a young star with about half the mass of the Sun. Orbiting the star is CD-35 2722 B, a brown dwarf approximately 37 times the mass of Jupiter. Brown dwarfs occupy a vague space between the largest planets and the smallest stars. The newly identified object orbits this brown dwarf.

      Researchers estimate its minimum mass to be around 0.9 times that of Jupiter and its orbital period to be roughly 170 days. Given its position in this cosmic framework, "exosatellite" is a more appropriate term for now. There is currently no universally accepted definition of an exomoon, which adds to the difficulty of classification when the host is a brown dwarf.

      How astronomers utilized a method from planet hunting to make this discovery.

      This artist’s impression shows a potentially habitable exomoon orbiting a giant planet.

      The team identified the object using radial velocity measurements with the CRIRES+ instrument on the VLT. This method looks for subtle gravitational wobbles caused by an unseen object in orbit and was notably used to discover the first exoplanet around a Sun-like star. In this case, the researchers applied this technique to a brown dwarf.

      Researchers believe that advancements in technology will ultimately allow them to apply the same method to smaller satellites and less massive hosts as well. The upcoming 39-meter Extremely Large Telescope from ESO is expected to significantly enhance this search. For the time being, CD-35 2722 has provided astronomers with a sufficiently large object that resembles a planet, orbiting something between a planet and a star.