Astronomers report possible first exomoon beyond Solar System

Astronomers may have found the first convincing evidence of a moon-like object beyond our Solar System, identifying a massive companion orbiting a brown dwarf in a distant star system.

The object is part of the CD-35 2722 system, which centres on a relatively young star with about half the mass of the Sun. A brown dwarf orbits the star, while the newly detected object appears to circle the brown dwarf, creating an unusual arrangement that challenges conventional distinctions between stars, planets and moons.

Kevin Hoy, an ESO student based in Chile and lead author of the study published in Nature, described the system as "super weird" compared with our own Solar System.

The researchers call the possible moon an exosatellite. It has at least the mass of Jupiter, while the brown dwarf it orbits is more than 30 times as massive as Jupiter.

Although the object is massive enough to qualify as a planet under some classification systems, it does not directly orbit a star. Instead, it circles another object that orbits a star, making its classification more complicated.

"This system is somewhat hard to define using Solar-System-based words like 'planet' and 'moon'," Hoy said. He is also affiliated with Chile's Universidad Diego Portales and the Millennium Nucleus of Young Exoplanets and their Moons (YEMS).

Alice Zurlo, YEMS director and a collaborator on the study, described the satellite as a giant gaseous body orbiting a highly massive companion several times the mass of Jupiter. Zurlo, also an astrophysicist at Universidad Diego Portales, said the system blurs the usual boundaries between stars, planets and moons.

Astronomers have been searching for moons beyond our Solar System for years, but no candidate has yet been confirmed conclusively. Although more than 6,000 exoplanets have been identified, evidence for possible exomoons remains limited.

Earlier in 2026, a team led by Quentin Kral reported possible signs of a satellite in the HD 206893 system based on observations from the European Southern Observatory's Very Large Telescope Interferometer. However, those observations did not establish a definitive detection.

To investigate CD-35 2722, Hoy, Zurlo and their colleagues used the CRIRES+ instrument on ESO's Very Large Telescope.

They applied the radial velocity method, which detects subtle changes in an object's motion caused by the gravitational pull of another body. As two objects orbit a shared centre of mass, even a smaller companion can produce a measurable wobble in the larger object's movement.

By analysing changes in the brown dwarf's motion, the researchers found evidence supporting the presence of another massive body orbiting it.

"As exotic as it is, this system is truly unique and represents a breakthrough: the first plausible detection of an exosatellite," Zurlo said.

Confirming such objects could help scientists better understand how planetary systems form and evolve, as well as explain why some systems differ significantly from our own.

Researchers expect the European Southern Observatory's upcoming Extremely Large Telescope (ELT), equipped with a 39-metre mirror and advanced instruments, to improve the search for exomoons, including smaller objects beyond the capabilities of current observatories.

The possible discovery also highlights the lack of a universally accepted definition of an exomoon. While an exosatellite refers to a satellite beyond our Solar System, an exomoon generally means a natural satellite orbiting a planet or another celestial body outside it.

The object in CD-35 2722 illustrates the difficulty of applying these labels to a body with a mass comparable to or greater than Jupiter's that orbits a brown dwarf rather than a star directly.