Astronomers Spot First Possible Moon Orbiting a Brown Dwarf

A consortium of astronomers observed the brown dwarf CD-35 2722 B, located 73 light-years away, with the CRIRES+ infrared spectrograph on ESO’s Very Large Telescope across 23 nights between October 2023 and February 2026. By applying the Doppler technique, they detected a regular velocity shift indicating a massive satellite—at least 0.9 times Jupiter’s mass—completing an orbit roughly every 170 days. This companion accounts for about 2.5 percent of the dwarf’s mass, a ratio exceeding that of Earth’s Moon and far surpassing the moons of Jupiter and Saturn.

The researchers eliminated other potential sources of the signal, including instrumental and atmospheric artifacts, and confirmed that the orbit lies safely between the Roche limit and the Hill radius, ensuring long-term stability. Published in Nature, the finding is described as an “exosatellite” and may reshape theories of moon formation around sub-stellar objects. Future telescopes like the Extremely Large Telescope could reveal even smaller moons, expanding the search for habitable environments beyond traditional planetary zones.