In the next two or three years, advances in NASA's Kepler telescope will allow astronomers to determine which planets outside our solar system could potentially sustain life. Exoplanets orbiting red dwarf stars are likely candidates for having Earth-like environments.
Over at Discovery, Ray Villard notes both A.) the optimal environmental conditions that red dwarf exoplanets would need to mimic Earth and B.) their ability to be detected vis-à-vis non-red dwarf exoplanets:
The planet will orbit a nearby red dwarf star found in surveys taken within 100 light-years of Earth. Why? Because red dwarfs are much more numerous than sun-like stars and so provide many more targets. Because red dwarfs are dim, planets orbiting them will not be as swamped by starlight and so their light is easier to measure.
The planet will be in the habitable zone around a red dwarf – a sweet spot where liquid water can remain stable on a planet's surface. The zone will be only a fraction the distance from the cool star as Earth's habitable zone is from our hotter Sun.
For those planets with orbits tilted edge-on to Earth, detecting them will be straightforward. Astronomers will see if the star dims slightly when the planet passes in front of it, or transits.
A planet in the habitable zone of a red dwarf would complete its racetrack orbit in just two weeks. This would allow multiple transits to be observed quickly. Also, because it is so close to the red dwarf, a planet is more likely to be in an orbit aligned along our line of sight, and will be more likely to be discovered transiting.
There are caveats, of course. Red dwarfs are unpredictable, and stellar flares can create massive amounts of UV radiation that would kill any surface life, barring organisms underwater. However, given the right conditions, these flares could instead bolster the ozone layer and create a greater degree of UV protection. In any case, NASA is dealing with sheer probabilities here. The ability to thoroughly investigate these planets — which are 100 or so light-years of Earth — is still way beyond our reach.
[Image Credit: David A. Aguilar (CfA)]