A celestial object circling a failed star 73 light-years from Earth has become the best candidate yet for an exosatellite – a moon outside our solar system. Detected with the European Southern Observatory’s Very Large Telescope (VLT) in Chile, the body orbits a brown dwarf in the CD-35 2722 system, and its mass is comparable to Jupiter’s. The finding, published in Nature, breaks a 30-year drought in exomoon confirmation and immediately complicates standard astronomical nomenclature.

Unlike rocky moons in the solar system, the object is a gas giant and does not trace a path around a planet. The brown dwarf it encircles has a mass roughly 30 times that of Jupiter and is itself in orbit around a larger star. “The satellite is clearly massive enough to be a planet, but it does not orbit a star,” explained Kevin Hoy of Chile’s Universidad Diego Portales, who led the study. “Being the third body in this system makes us want to call it a moon, even though it bears no resemblance to the small rocky moons we know.”

Italian researchers from the National Institute for Astrophysics (INAF) contributed to the analysis, using the VLT’s radial-velocity capabilities to measure tiny wobbles induced in the brown dwarf by the orbiting object. The team describes the system as a unique laboratory where the boundaries between stars, planets and moons dissolve. “In the solar system there is a clean distinction, but here everything is much harder to delineate,” said Alice Zurlo of Diego Portales and INAF.

For now, the discovery remains a “plausible detection”, pending formal classification. Astronomers view it as a proof of concept that exosatellites exist and can be found with current instruments, even if defining them requires a broader framework. The next leap is expected from the Extremely Large Telescope (ELT) and its Italian-led ANDES spectrograph, which will probe for smaller, more familiar exomoons with far greater sensitivity, offering a new window into the architecture of alien planetary systems.