The closest inhabitable planet may only be about 13 light-years away, says a new study from Harvard based on data from NASA's Kepler mission. The study, conducted by Harvard University grad student Courtney Dressing and astronomer David Charbonneau at the Harvard-Smithsonian Center for Astrophysics, was based on estimates of stars' masses, temperatures, and several other factors to determine the habitable zone.
This is a rapidly-growing sector of astronomy: in 2000, scientists had only confirmed 33 planets, all gas giants. Now, with Kepler's candidates included, possible planets number 3,300.
Dressing and Charbonneau found evidence of 95 planets orbiting 64 stars, 60 percent of which were smaller than Neptune, the smallest gas giant. "That's a remarkably large number," Dressing said at a press briefing.
The Kepler was launched in March 2009 and has since then been investigating stars in the Cygnus and Lyra constellations-- about 158,000 of them. It has found that about 80 percent of the stars in our galaxy are red dwarfs, and that about 6 percent of them have planets orbiting in the habitable range. Extending those numbers to the rest of the galaxy, that means our tiny corner of the universe could have anywhere between 9.6 billion and 19.2 billion Earth-like planets.
The Christian Science Monitor reports that with these data, there should be at least three Earth-size planets orbiting habitable zones of stars within 33 light-years of Earth, which is within easy reach for the James Webb Space Telescope, due to launch in 2018.
Scientists have long regarded red dwarfs as likely candidates for hosting habitable planets. Because of their longevity, life would have plenty of time to grow and evolve, assuming it manages to get a metaphorical foot in the door. With the abundance of red dwarfs in the Milky Way system, this could show definitively that our solar system, with a hotter and more volatile star, could be the exception rather than the rule.
Astronomers have also believed for a long time that the kind of orbit a planet would have around a red dwarf would keep one side of the planet in shadowy deep freeze and the lit side baking-hot, but a satellite with oceans and an atmosphere would be able to more evenly the distribute the heat, making the planet hospitable to life. "I think that with hindsight, we see that as a myopia for having grown up around a sun-like star," Charbonneau told the CSM.
