'Alien Earth' is among eight new far-off planets
One of eight new planets spied in distant solar systems has usurped the title of "most Earth-like alien world". All eight were picked out by Nasa's Kepler space telescope, taking its tally of such "exoplanets" past 1,000. Only three sit safely within the habitable zone of their star, and one in particular is rocky, like Earth, as well as only slightly warmer.
The find was revealed at a meeting of the American Astronomical Society. The three potentially habitable planets join Kepler's "hall of fame", which now boasts eight fascinating planetary prospects.
And researchers say the most Earth-like of the new arrivals, known as Kepler 438b, is probably even more similar to our home than Kepler 186f - which previously looked to be our most likely twin.
At 12% larger than Earth, the new claimant is bigger than 186f but it is closer to our temperature, probably receiving just 40% more heat from its sun than we do from ours. So if we could stand on the surface of 438b it may well be warmer than here, according to Dr Doug Caldwell from the Seti (Search for Extra-Terrestrial Intelligence) Institute in California.
An artist's view of Kepler 186f, which experts say has now been pipped as "most Earth-like" known exoplanet
"And it's around a cooler [red dwarf] star... so your sky would look redder than ours does to us," Dr Caldwell said.
'Star Trek' scenario
Even once scientists have anointed a candidate as a confirmed exoplanet, the question of whether or not it is "Earth-like" is a fraught one, with fuzzy boundaries. The size of the habitable, or "Goldilocks" zone, where a planet is far enough from its sun to hold water but not so distant that it freezes, depends on how confident scientists want to be with their guess-work.
According to Dr Cardwell, just three of the eight new exoplanets can be confidently placed in that zone, and only two of those are probably rocky like the Earth.