Artist’s concept showing an Earth-like planet orbiting a star that has formed a stunning "planetary nebula"
Astronomers have discovered eight new exoplanets that may be capable of supporting life as we know it, including what they say are the two most Earthlike alien worlds yet found.
All eight newfound alien planets appear to orbit in their parent stars' habitable zone — that just-right range of distances that may allow liquid water to exist on a world's surface — and all of them are relatively small, researchers said.
"Most of these planets have a good chance of being rocky, like Earth," study lead author Guillermo Torres, of the Harvard-Smithsonian Center for Astrophysics (CfA), said in a statement.
The haul doubles the number of known habitable-zone planets that are potentially rocky, study team members said.
The newly discovered worlds were all detected by NASA's prolific Kepler space telescope, then confirmed using observations by other telescopes and a computer program that assessed the statistical probability that they are bona fide planets (as opposed to false positives).
While none of the eight is a true "alien Earth," two of them — known as Kepler-438b and Kepler-442b — stand out for their similarities to our home planet (though both worlds orbit red dwarfs, stars that are smaller and dimmer than Earth's sun).
"We don't know for sure whether any of the planets in our sample are truly habitable," co-author David Kipping, also of the CfA, said in the same statement. "All we can say is that they're promising candidates." [The Search For Another Earth (Video)]
Such hedging is unavoidable at this point, because researchers just don't have enough information. For starters, there's the uncertainty about the planets' composition, as evidenced by the estimated rockiness probabilities. (Nobody knows for sure where the dividing line lies between rocky and gaseous worlds, in terms of planet size.)
Furthermore, a planet's surface temperature is highly dependent on the composition and thickness of its atmosphere, and nothing is known about the air surrounding Kepler-438b, Kepler-442b or any of the other newfound worlds.
And some scientists employ a more restrictive definition of "habitable zone" than others. Indeed, study team member Douglas Caldwell, who presented the results today (Jan. 6) at the annual winter meeting of the American Astronomical Society (AAS) in Seattle, said that only three of the newly confirmed planets are "securely" in the habitable zone.
But he's not discounting the life-hosting chances of the other five.
"All of these planets are small, all of them are potentially habitable — and, in fact, have a more than a 50 percent chance of being in the slightly extended habitable zone — and all are interesting," Caldwell, who's based at the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, said during a AAS press briefing today.
