Exoplanets have found a permanent place in the public imagination, probably because of the possibility of finding an Earth twin: a planet where life as we know it (either extraterrestrial or, eventually, our own) could survive. While we’re not there, yet, a NASA press conference today suggests we’ve come closer to this goal: the first known planets that could plausibly support life.
A nearby star named Kepler-62 turns out to harbor five worlds, two of which are the smallest exoplanets known to orbiting within their star’s habitable zone. This means temperatures on them would allow for liquid water to exist (a requirement for life). In fact, scientific models suggest that both could be “water worlds,” completely covered with global oceans. “These two planets are our best candidates for planets that might be habitable,” said William Borucki, Kepler science principal investigator, at the conference.
The two new exoplanets, known as Kepler-62e and Kepler-62f, are the farthest out of the five that orbit Kepler 62, a star smaller and cooler than the sun that lies about 1,200 light-years away. The radius of Kepler-62e is about 60 percent bigger than Earth’s, and it takes about 122 days to orbit its star. Kepler-62f’s radius is only about 40 percent larger than Earth’s, and its year lasts some 267 days.
The conference also announced a third intriguing exoplanet, Kepler-69c, which orbits within the habitable zone of its star, Kepler-69 (a sun-like star about 2,700 light-years away). This world has a radius 70 percent larger than Earth’s and orbits its star in 242 days.
The masses of these planets are too small for scientists to measure, so scientists can only speculate as to their makeup at this point, but every other known exoplanet of similar size has turned out to be rocky, similar to Earth. The Kepler-62 planets were reported today in Science and Kepler-69c today in The Astrophysical Journal.
Astronomers found these worlds thanks to NASA’s Kepler spacecraft, which launched in 2009 specifically to seek out Earth-like exoplanets. It searches for stars with occasional dips in brightness, potentially caused by an exoplanet crossing its shining face. From that minor dimming, akin to a fly buzzing in front of a car’s headlight, astronomers can piece together a surprising amount of information.
Kepler’s impressive and prodigious results (more than 2740 planet candidates found so far) have never before included candidates so close to an Earth twin, but with any luck, and more research, they soon will.
“We are on the verge of the discovery of so many very exciting planets!” said Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics at the conference.