Gliese 581g has a mass about three to four times that of Earth.
Astronomers have discovered a new planet with the closest conditions they have found so far to those on earth.
The planet is orbiting the star, Gliese 581, 20 light years away.
Gliese 581g lies some 20 light-years away in the star's 'Goldilocks zone' - a region surface temperatures would allow the presence of liquid water.
Scientists say that it could also potentially have an atmosphere.
Their findings, made with the Keck telescope in Hawaii, appear in the Astrophysical Journal.
The researchers, from the University of California at Santa Cruz and the Carnegie Institution of Washington, have been studying the movement of the planet's parent star, a red dwarf called Gliese 581, for 11 years.
Their observations revealed a number of exoplanets spinning around the star.
The BBC reports they recently discovered two new alien worlds, bringing the number of planets orbiting Gliese 581 to six.
Gliese 581g has a mass about three to four times that of Earth. It orbits its sun in 37 days and is thought to be a rocky world. It has enough gravity to possibly have an atmosphere.