Planetary-Mass Exosatellite Found Orbiting Brown Dwarf

Astronomers have detected a planetary-mass exosatellite orbiting the brown dwarf companion CD-35 2722 B, according to research published online in Nature on July 22, 2026. This discovery, made through radial velocity measurements, provides compelling evidence for an exomoon-like object with a mass comparable to Jupiter. The brown dwarf, CD-35 2722 B, is part of a binary system, and the detected exosatellite orbits this substellar companion.

The findings represent a significant advancement in the search for exomoons, which are celestial bodies orbiting planets outside our solar system. While numerous exoplanets have been identified, the detection of exomoons has been considerably more challenging due to their smaller size and fainter signals. The radial velocity method used in this study measures the slight wobble of a star or brown dwarf caused by the gravitational pull of an orbiting object. By analyzing these subtle shifts in velocity, researchers can infer the presence and mass of unseen companions.

The exosatellite's mass is estimated to be similar to that of Jupiter, making it a substantial object. Its host, CD-35 2722 B, is a brown dwarf, an object more massive than a planet but not massive enough to sustain nuclear fusion in its core like a star. The detection of such a large moon-like object around a brown dwarf opens new avenues for understanding planetary formation and satellite evolution in diverse astrophysical environments. Further observations will be crucial to confirm the exosatellite's orbital characteristics and composition.