It’s a bit less possible now that we’re alone in the universe. The $600-million Kepler Space Telescope, launched five years ago to identify planets, has spotted more than 3,800 and confirmed 966 of them. The last one, fifth planet of a star in the constellation Cygnus, was reported yesterday in the journal Science and in a NASA press briefing. And it just might be the real deal.
Here’s the abstract:
“The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces.
We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star’s radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.”
The telescope detected the faraway world by observing how its passage (transit) reduced the light from its red dwarf star. Regular transits also allowed scientists to calculate the planet’s orbit. Because the alien planet’s star is only about half as big as our Sol, it is cooler and dimmer from the planet. However, Kepler-186f’s tighter orbit (130 days) should still make the planet warm enough to prevent seas from freezing.
Says astrophysicist coauthor Justin R. Crepp of Notre Dame:
“The host star, Kepler 186, is an M1-type dwarf star, which means it will burn hydrogen forever, so there is ample opportunity to develop life around this particular star, and because it has just the right orbital period water may exist in a liquid phase on this planet…. What’s special about this discovery is that the planet is in the habitable zone [also called “the Goldilocks zone”]. It’s this annulus around this star where we think it’s just the right temperature. Not too hot, not too cold. Where you can have water in a liquid form which might be conducive to life.”
“This is a first, validated Earth-size planet in the habitable zone of another star…. [But] just because a planet is in the habitable zone doesn’t mean it is habitable,” says the study’s lead author, Dr. Elisa Quintana of the SETI Institute and NASA’s Ames Research Center in Mountain View, California. “This is sort of a first step.”
We know the size of the new planet, but not its mass and composition. Scientists are fairly sure it is rocky, not a gas giant. Because Kepler-186f is beyond telescope range, we cannot measure its atmosphere and greenhouse effect, and without that knowledge, we can’t call it “an Earth twin,” only “an Earth cousin” thus far.
Nonetheless, in a comment accompanying the breakthrough study, Yudhijit Bhattacharjee of Science states that “the finding could open a wide new hunting ground for extraterrestrial life” orbiting other red dwarf stars, which make up three-quarters of the Milky Way.
Canadian coauthor Jason Rowe has added:
“If Earth-like planets are common around stars like that, we have potentially habitable zone planets in our own backyard—planets that already might be receiving the first radio broadcasts that came from the Earth.”