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The European Southern Observatory (ESO) has announced a potential discovery that could be the first moon outside our Solar System (sometimes called an “exosatellite”). The result requires confirmation.
Meet the CD-35 2722 System
The system at the center of this find is CD-35 2722, which the team describes like “three nested Russian dolls.” The main star, CD-35 2722, is young and has a mass about 0.5 times that of our Sun (0.5 M⊙). Orbiting that star is a brown dwarf, a “failed star” whose mass is more than a planet’s but not enough to trigger the nuclear fusion that makes true stars, with a mass greater than 30 times the mass of Jupiter (30 M_J).
The new object detected orbits that brown dwarf rather than the star, and it’s at least as massive as Jupiter (≥1 M_J). Lead author Kevin Hoy, an ESO student, calls the system “super bizarre,” noting how it blurs the usual labels like “moon” or “planet.”
How They Spotted It
The discovery used the Very Large Telescope (VLT) in Chile, with the CRIRES+ spectrograph. The team applied the radial velocity method to detect the gravitational tug the candidate exosatellite exerts on its brown dwarf host. That technique dates to the first exoplanet found around a Sun-like star in 1995 and detects small shifts in the spectrum due to the Doppler effect.
An international group worked on the study, including co-author Alice Zurlo, director of the YEMS program. Zurlo describes the system as a “real scientific headache,” citing the difficulties in classifying objects like this.
What Comes Next
This detection is strong evidence but not a formal confirmation. There is no official definition for “exomoon,” which complicates classification. The result may guide future searches.
Looking ahead, the Extremely Large Telescope (ELT), with its 39-meter mirror, should allow astronomers to search for smaller exomoons and address current measurement and classification issues.
If confirmed, the CD-35 2722 detection would be among the first candidates for moons beyond the Solar System and would inform models of planetary system formation and evolution. Searches for such objects continue, and advances in telescope technology will expand what can be measured.
