According to French researchers, the planet `Gliese 581d` is located at the colder outer edge of the "Goldilocks zone", or habitable zone, where liquid water can be sustained.
They also believe the atmosphere of the exoplanet may keep things warm enough for water, the BBC reported.
Gliese 581d was discovered along with another planet Gliese 581c in 2007, occupying the outer and inner edges of the Goldilocks zone, respectively.
Gliese 581c was soon determined to be too close to its host star to sustain water, with a surface temperature exceeding 1,000C.
Conversely, the outlying planet 581d -- with a mass about six times that of the Earth and twice its size -- was initially taken to be too cold to have liquid water.
Now, researchers at the Institute Pierre Simon Laplace in Paris have run computer simulations of the planet`s atmosphere and argued that it is likely to contain high concentrations of carbon dioxide.
Reporting their findings in Astrophysical Journal Letters, the researchers contend that conditions could be suitable for oceans of liquid water as well as clouds and rainfall.
However, Gliese 581d`s denser air and dim red light from its host star would make for a murky environment that would be toxic to humans.
Robin Wordsworth, a member of the research team, said that the findings were further evidence that the sheer variety of planets and environments far outpaced that which we see in our own Solar System.
He said that the simulations are tantamount to a first definitive claim for a habitable exoplanet.
"This discovery is important because it`s the first time climate modellers have proved that the planet is potentially habitable, and all observers agree that the exoplanet exists," Dr Wordsworth was quoted as saying.
"The Gliese system is particularly exciting to us as it`s very close to Earth, relatively speaking. So with future generations of telescopes, we`ll be able to search for life on Gliese 581d directly.