Just 20 years ago, astronomers imagined that planets beyond the Solar System would be more or less like the ones we know: small, rocky worlds like Mercury, Venus, Earth and Mars orbiting relatively close to their stars, and big, gassy ones like Jupiter, Saturn, Uranus and Neptune, farther away. (Even then, Pluto was recognized as an oddball, though it hadn’t been demoted yet.) Then the first actual exoplanet was discovered, and it turned out to be a big, gaseous world orbiting ridiculously close to its star. Dozens of others very much like it soon turned up, and the astronomers’ preconceptions were abruptly laid to rest.

But at least these so-called “hot Jupiters” actually orbited a star. Not so for a new planet just reported in the journal Astronomy and Astrophysics. The object, known only as CFBDSIR2149, appears to be a planet from four to seven times as massive as Jupiter, floating along with a cluster of stars known as the AB Doradus Moving Group — but tethered to no one star in particular.