Livable super-Earths? Two candidates among Kepler's latest finds.
Researchers unveiled a total of three planets Thursday, including two potentially livable super-Earths. The discoveries bring the Kepler team closer to its goal.
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(Sorry "Waterworld" fans, no post-apocalyptic planet here. It was born that way.)Skip to next paragraph
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The system's age is of no small interest. Assuming that the two planets are indeed habitable and that their stellar system has been at least as kind to them as the solar system has been to Earth over its 4.5 billion-year history, 7 billion years in principle is plenty of time for life to emerge and evolve into ever-more-complex forms.
The second of the new habitable-zone planets is the fifth, most distant planet yet detected in the Kepler 62 system. It orbits Kepler 62 once every 267 days. The planet, Kepler 62-f, is about 40 percent larger than Earth.
Here, too, the team has no true mass estimate. The researchers have inferred the planet's composition based on studies of other extra-solar planets of comparable size for which mass estimates exist. Those planets are rocky.
While it falls within its star's habitable zone, 62-f would have to build up an overabundance of carbon dioxide to provide enough of an atmospheric greenhouse effect to warm the planet's surface.
If an astronaut were to arrive at the planet, keeping his or her helmet on would be a good idea, Dr. Kaltenegger suggests.
In addition to the five-planet system, Dr. Borucki and colleagues also announced the discovery of a second planet orbiting a star tagged Kepler 69, which lies 2,700 light-years from Earth in the constellation Cygnus. The star is about 90 percent of the sun's size and carries about 80 percent of the sun's mass. This system is in its infancy: It's only about 400 million years old.
Dubbed Kepler 69-c, the planet is about 70 percent larger than Earth and orbits its host star once every 242 days. Like Venus, Kepler 69-c orbits at the inner edge of a habitable zone, suggesting that it likely is a bit too toasty. Uncertainties in estimates of 69-c's orbit, however, could mean it also orbits deeper within the habitable zone.
Still, if the habitable zone represents a region between fire and ice, 69-c "is orbiting closer to the fire than the ice," says Thomas Barclay, a researcher with the the Bay Area Environmental Research Institute in Sonoma, Calif., and a member of the Kepler team. "We consider this perhaps more of a super-Venus than super-Earth" until the researchers have a better estimate of the extent of the star's habitable zone.
For all its continued success, Kepler is examining a patch of space in which it can be difficult to conduct follow-up studies of the planetary systems that are discovered. But that is slated to change, team members say.
In April 2017, NASA is planning to launch the Transiting Exoplanet Survey Satellite. The $200-million mission is designed to use Kepler's approach to detecting planets to explore some 2 million stars, many of which will be much closer to home than the stars in Kepler's field of view.
The detection technique tracks the periodic dimming created by a transiting planet as it passes in front of its host star.
New, closer planet systems will be far easier pickings for a new generation of space telescopes to study in detail – including a search for signs of life that might be revealed in the composition of an extra-solar planet's atmosphere.
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