Slight, fast, but regular wobbles of nearby small M-dwarf star Gliese 876 showed evidence for a planet with a likely mass slightly higher than a minimum six times the mass of Earth.
The planet's small mass indicates that it is likely terrestrial in nature, similar in composition to the inner planets of our Solar System.
If indeed made predominantly of rock, the planet's surface gravity would not even be able to contain the gasses of a Jupiter-like planet.