New ‘Exomoon’ Detection in Columba Star System Challenges Cosmic Labels | ESO
Using the European Southern Observatory’s Very Large Telescope (VLT), astronomers have found an object in another planetary system that challenges astronomical labels. The object resembles a moon in that it orbits another object that in turn orbits a star. However, the newly found ‘moon’ is itself as massive as a planet, and the object it orbits is neither a planet nor a star. This video summarizes the discovery.
Observations made with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) have revealed evidence for a moon-like object in the CD-35 2722 system. Unlike moons in our Solar System, the newly found object does not orbit a planet, raising questions about what to name it. Instead, it circles a brown dwarf, an object larger than a planet, that orbits the CD-35 2722 star. If confirmed, this could be the first ‘moon’ discovered outside our Solar System. CD-35 2722 b is a gas giant exoplanet that orbits a M-type star. Its mass is 29.5 Jupiters, it takes 867.6 years to complete one orbit of its star, and is 67 AU from its star. Its discovery was announced in 2011.
Kevin Hoy, an ESO student in Chile and lead author of the study published today in Nature, describes the system he spent months analyzing as “super weird” compared to our own. The biggest and most massive object in this young system is the star CD-35 2722 that has about half the mass of the Sun. The star is being orbited by a brown dwarf, an object too massive to be a planet but too small to be a star. The newly discovered object orbits this brown dwarf.
“This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’,” states Hoy, who is also affiliated with the Universidad Diego Portales and the Millennium Nucleus of Young Exoplanets and their Moons (YEMS) in Chile. The new object the team calls an exosatellite is at least as massive as Jupiter while the brown dwarf has more than 30 times the mass of Jupiter. “The exosatellite is clearly massive enough to be a planet, but it does not orbit a star, though it orbits an object that orbits a star," says Hoy. "Being the third wheel in this system makes us want to call it a moon, even if it is nothing like the small, rocky moons we have in our system.”
This exosatellite or ‘exomoon’, a natural satellite outside our Solar System, is difficult to label, given the differences in this system compared to our own. Alice Zurlo, YEMS Director and collaborator on the study explains: “The satellite we report is a giant gaseous body orbiting a highly massive companion, itself several times the mass of Jupiter.”
“We have a clear delineation between the planets and the Sun in the Solar System, so defining things like moons is simple. In the CD-35 2722 system, where we are blurring the lines between stars, planets, and moons, the whole thing becomes more complicated to describe,” adds Zurlo, who is also an astrophysicist at Universidad Diego Portales.
Regardless of what to call this object, astronomers have been trying to detect satellites outside our Solar System for years, but none has yet been confidently detected. Therefore, despite the over 6,000 exoplanets discovered to date, only a few exomoon candidates have been spotted and the evidence to support them is limited.
For the CD-35 2722 observations, Hoy, Zurlo and their team used the CRIRES+ instrument on ESO’s VLT, employing the method that was used to find the first exoplanet around a Sun-like star. They applied this radial velocity method to detect small wobbles on the brown dwarf caused by the object orbiting it, finding what the team believe to be strong evidence for this ‘moon’. “As exotic as it is, this system is truly unique and represents a breakthrough: the first plausible detection of an exosatellite,” says Zurlo.
Written by: M. Lopes
Edited by: V. González
Footage and photos: ESO, L. Calçada, M. Kornmesser, C. Malin, B. Tafreshi
Duration: 1 minute, 29 seconds
Date: July 22, 2026
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