The celestial body, known as GJ 581g, has a climate that's not too dissimilar from that found on Earth, according to scientists at the Lick-Carnegie Exoplanet Survey.
"The estimated equilibrium temperature of GJ 581g, is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star," the researchers said in a paper submitted to The Astrophysical Journal.
"That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of RV [Radial Velocities] indicates that eta-Earth, the fraction of stars with potentially habitable planets, is likely to be substantial," the astronomers said.
Radial velocity measures the speed at which an object is moving toward or away from the observer. Scientists use the measurement to detect planets based on the gravitational pull of the stars around which they orbit.
GJ 581g is "a minimum mass 3.1 M_Earth planet orbiting at .146 AU with a period of 36.6 days," said the scientists from Lick-Carnegie.
"This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume limited samples of stars in the immediate solar neighborhood suggests that eta_Earth could well be on the order of a few tens of percent," said the team.
"If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets," the said.
The term "Class M" was coined by Star Trek creatory Gene Roddenberry, who used it to describe planets that had Earth-like temperatures and atmospheres in the fictional TV series.