Astronomers may have found the first moon beyond our Solar System, but the mysterious object is unlike any moon we know. Observations from the European Southern Observatory’s Very Large Telescope (ESO’s VLT) have uncovered evidence of an enormous moon-like body in the CD-35 2722 star system. Rather than orbiting a planet, this unusual object circles a brown dwarf, a celestial body more massive than a planet but not massive enough to become a star.
If confirmed, the discovery could mark the first detection of a natural satellite outside our Solar System, potentially changing how astronomers define moons and planets.
A Bizarre Star System Unlike Our Own
Kevin Hoy, an ESO student based in Chile and lead author of the study published in Nature, spent months examining the CD-35 2722 system. He describes its unusual arrangement as “super weird” compared with our own Solar System.
At the center of this relatively young system is CD-35 2722, a star with approximately half the Sun’s mass. Orbiting the star is a brown dwarf, an object that occupies the murky boundary between planets and stars. Brown dwarfs are generally too small to sustain the hydrogen fusion that powers ordinary stars, yet they are more massive than planets.
The newly identified object orbits this brown dwarf, creating a remarkable arrangement in which a massive satellite circles an object that itself revolves around a star.
“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 researchers refer to the newly detected object as an exosatellite. It has at least as much mass as Jupiter, while the brown dwarf it orbits is more than 30 times as massive as Jupiter. This makes the possible moon far more massive than any natural satellite in our Solar System.
“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.”
A Giant Exomoon That Challenges Cosmic Definitions
The unusual discovery highlights a fundamental problem with applying familiar astronomical labels to objects found in distant star systems.
An exosatellite is a natural satellite located beyond our Solar System, while the term exomoon generally refers to a natural satellite orbiting a planet or another celestial body outside our Solar System. However, astronomers have not established a universally accepted definition of an exomoon.
That distinction becomes especially important in the CD-35 2722 system, where the possible moon is itself massive enough to be considered a planet under some classification schemes.
Alice Zurlo, director of YEMS and a 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.”
The arrangement is very different from the familiar structure of our Solar System, where planets orbit the Sun and moons orbit planets.
“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.
Scientists Search for the First Confirmed Exomoon
Astronomers have spent years looking for moons around objects beyond our Solar System, but no candidate has yet been detected with enough certainty to establish a confirmed discovery.
That makes the latest findings particularly significant. Although scientists have identified more than 6,000 exoplanets, only a handful of possible exomoons have emerged from observations, and the evidence supporting them remains limited.
Earlier in 2026, a research team led by Quentin Kral reported possible signs of a satellite in the HD 206893 star system. Their observations, obtained with ESO’s Very Large Telescope Interferometer, suggested that a moon-like companion might exist, but they did not establish a definitive detection.
The CD-35 2722 system now offers another promising opportunity, supported by measurements of how the suspected moon affects the motion of its larger companion.
How Astronomers Detected the Possible Alien Moon
To investigate CD-35 2722, Hoy, Zurlo, and their colleagues used the CRIRES+ instrument installed on ESO’s Very Large Telescope.
The team applied a technique known as the radial velocity method, which was also used to discover the first exoplanet orbiting a Sun-like star.
This approach works by measuring extremely small changes in an object’s motion. When two celestial bodies orbit one another, their mutual gravitational attraction causes both to move around a shared center of mass. Even a much smaller companion can produce a detectable wobble in the larger object’s motion.
By examining subtle changes in the brown dwarf’s motion, the researchers identified what they consider strong evidence that another massive body is orbiting it.
“As exotic as it is, this system is truly unique and represents a breakthrough: the first plausible detection of an exosatellite,” says Zurlo.
A New Era in the Search for Alien Moons
Confirming moons beyond our Solar System would do more than add another category of objects to astronomical catalogs. These discoveries could help researchers understand how planetary systems form, how their components interact, and why some systems develop structures dramatically different from our own.
Future observations could also reveal whether massive satellites like the one proposed in CD-35 2722 are rare exceptions or part of a much broader population of unusual celestial objects.
ESO’s upcoming Extremely Large Telescope (ELT) is expected to play a major role in that search. Equipped with an enormous 39-meter mirror and advanced scientific instruments, the telescope will give astronomers the ability to detect smaller exomoons that are currently beyond the reach of existing observatories.
As scientists begin identifying more satellites in distant planetary systems, they may discover that familiar distinctions between stars, planets, and moons are not as universal as once assumed.
What Counts as an Exomoon?
A satellite is any object that travels around another object. Satellites can be natural (like our own moon) or artificial (like a spacecraft).
An exosatellite is a satellite located outside our Solar System. The term exomoon generally describes a natural satellite orbiting a planet or another object beyond our Solar System, although astronomers have not agreed on an official definition.
The possible companion in CD-35 2722 illustrates why that definition matters. With a mass comparable to or greater than Jupiter’s, it resembles a planet in size and composition, yet its orbital relationship with the brown dwarf makes it a candidate for an entirely different classification.
