In the search for habitable worlds beyond our solar system, the biggest, hottest opportunities may be found around the smallest, coolest stars. Called M dwarfs, these stars have a mere fraction of the sun's mass and luminosity but are more than 10 times as numerous. Planets circling an M dwarf must be in a close orbit to the star to be warm enough for life, like campers huddling around a small fire. This proximity makes them relatively easy for planet hunters to find, and the prevalence of M dwarfs means there are plenty nearby to investigate.
Astronomers are now gearing up for such an exploration. Multiple independent projects are already monitoring nearby M dwarfs, and a host of new telescopes and satellites are in the works to spot planets orbiting them, including NASA's Transiting Exoplanet Survey Satellite (set to launch in 2017). These efforts make the imminent discovery of potentially habitable M dwarf planets a near certainty. Whether all those bodies will actually prove to be habitable, however, is much less clear: the same sunny properties that make promising M dwarf planets so easy to find may also preclude the possibility for life on those worlds.
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