Is This the First Exomoon? When Planets and Moons Defy Definition

Astronomers may have found the first convincing evidence of a moon-like object beyond our Solar System — but calling it a "moon" turns out to be surprisingly complicated.

Using the CRIRES+ instrument on ESO's Very Large Telescope, researchers detected evidence of a massive object orbiting a brown dwarf in the young CD-35 2722 system. The newly detected object is at least as massive as Jupiter, while its brown-dwarf companion is more than 30 times Jupiter's mass. That brown dwarf, in turn, orbits a star.

So what exactly have astronomers discovered: a moon, a planet, an exosatellite — or something that shows our familiar astronomical labels aren't quite ready for the diversity of other planetary systems?

Join SETI Institute senior planetary astronomer Dr. Franck Marchis and lead author Kevin Hoy as they explore how astronomers detected this unusual object, why previous exomoon candidates have been so difficult to confirm, and what this strange system could teach us about how planets, moons, and brown dwarfs form.

Press release: https://www.eso.org/public/news/eso2610/ 
Paper: https://www.nature.com/articles/s41586-026-10751-w