Now the verdict is in: Gliese 581g is an ex-planet, not an exoplanet.
The same group of astronomers has also inferred a type of exoplanet that fits in between the rocky planets and the gas giants.
exoplanet astronomy—the search for planets orbiting other stars—has two major goals.
an extrasolar planet; a planet that orbits a star outside of the solar system
exo- + planet
See extrasolar planet.