Astronomers spot first ‘exosatellite’ in three-tiered star system

Using the ESO’s Very Large Telescope, astronomers have detected the first plausible exosatellite — a moon-like object outside our solar system.

The system, CD-35 2722, has a star orbited by a brown dwarf, which itself is orbited by a Jupiter-sized object. That third object is what researchers are calling an “exosatellite.”

Lead author Kevin Hoy described the system as “super weird” because the object is planet-sized but doesn’t orbit a star directly. Alice Zurlo of YEMS said the discovery blurs traditional lines between stars, planets and moons.

The team used the radial velocity method to detect tiny wobbles caused by the orbiting object. Despite 6,000+ exoplanets found to date, no exomoon had been confidently confirmed until now. Scientists expect exosatellites could be common — 6 of 8 planets in our solar system have moons — but they are hard to detect due to their small size.

Researchers say the discovery, similar in impact to the first exoplanet found in 1992, could lead to many more exosatellite detections in the coming years.