Washington, Jan 7: The "Does human life exist beyond Earth" debate just scored another talking point with the discovery of eight new planets within the so-called "Goldilocks" -- or habitable -- zone of their stars.
Astronomers with the Harvard-Smithsonian Center for Astrophysics, (CfA), announced their findings at a meeting of the American Astronomical Society, CNN reported.
To be considered habitable, exoplanets must orbit within a distance of their stars in which liquid water can exist on the planet's surface, receiving about as much sunlight as Earth.
Hence the Goldilocks zone: Too much sunlight and the water would boil away as steam, too little, and the water would freeze.
Among the eight, scientists say two are the most similar to Earth of any known exoplanets to date.
"Most of these planets have a good chance of being rocky, like Earth," lead author Guillermo Torres of the CfA said in a release.
The discoveries of Kepler-438b and Kepler-442b are the latest in several advancements scientists have made to find signs of possible life in the universe.
At a panel held last summer at NASA headquarters in Washington, astronomers said they were "very close in terms of technology and science to actually finding the other Earth."
That's due in part to the Kepler Space Telescope. The planet-hunting Kepler probe, launched in 2009, finds planets by looking for dips in the brightness of a star as a planet transits, or crosses, in front of that star.
Christine Pulliam of CfA said the team of scientists monitored data for more than 160,000 stars, which led them to the eight new planets.
The couple most like Earth, Kepler-438b and Kepler-442b, both orbit red dwarf stars, which are cooler and smaller than the Earth's sun.
Kepler-438b's diameter is 12 percent bigger than Earth and has a 70 percent chance of being rocky, which means the surface of the planet appears to be like Earth's.
Kepler-442b is about one-third larger than Earth with a 60 percent chance of being rocky. Scientists give it a 97 percent chance of being in the habitable zone, but caution that the estimations aren't certain.
"We don't know for sure whether any of the planets in our sample are truly habitable," second author David Kipping of the CfA said in a release.
"All we can say is that they're promising candidates."
And even if there was confirmation, Christine Pulliam of CfA said teams are "still a couple of generations of telescope development away," from even seeing them, much less visiting.
Kepler-438b is 470 light-years away and Kepler-442b is 1100 light years away, according to CfA.
"That's a little far away," Caldwell said, "We need to get to Mars first."