An analysis of thousands of stars in the Kepler space telescope's database, found 95 possible planets orbiting red dwarfs. Of these, three are Earth-sized candidates in the habitable zone – the region around a star where liquid water can exist. Statistically, that means 6 per cent of all red dwarfs in our galaxy should have rocky planets in the habitable zone.
Most of the stars nearest to us are red dwarfs, including the closest, Proxima Centauri. Based on the distribution of red dwarfs in the Milky Way, Dressing estimates that a potentially habitable planet is only 13 light years away.
Due to orbital geometries, the odds that a given planet transits its star so that we can see it are just 1 in 50, so there's a chance the nearest habitable world will not be one that surveys like Kepler can see. The odds are better that we can see a habitable planet transit within 100 light years of Earth. That's still near enough for planned observatories to check its atmosphere for gases produced by life on Earth, such as a large amount of oxygen.
NASA is currently considering two planet-hunting telescopes that could help find such a nearby world: the Transiting Exoplanet Survey Satellite (TESS) and the Fast Infrared Exoplanet Spectroscopy Survey Explorer (FINESSE). One of these missions is expected to be selected this spring for launch in 2017.
Even if neither space mission goes ahead, large telescopes on the ground should also be able to detect gases like oxygen in exoplanet atmospheres. Ignas Snellen of the University of Leiden in the Netherlands and colleagues think that, once a habitable planet around a red dwarf is found, planned facilities such as the European Extremely Large Telescope could detect such gases in its atmosphere within three to four years.
"We could be in the business of studying the atmospheres of habitable worlds 10 years from now," says David Charbonneau, also of the Harvard-Smithsonian Centre for Astrophysics. If NASA launches the missions the space telescopes and we get lucky with analysis of Kepler data to confirm exoplanets, then we could be studying the atmospheres by 2017 or 2020 with space or ground based systems.