But the Kepler planets will be too far away –- hundreds or thousand of light-years - for any follow-up observations to be able to determine if they are inhabited. All we will have from the Kepler data is planet mass, diameter, orbital period, and parent star type.
The Earth clones will forever remain a blip on the exoplanet radar when it comes to determining true habitability.
But enough exoplanet research has been done so far that a cautious prediction can be made about where the first inhabited planet will be found.
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.
But there is one big catch. Young red dwarfs have a petulant youth stretching over billions of years. Titanic stellar flares erupt without warning and blast out lethal doses of ultraviolet radiation. Ocean life on a planet may be safe from the UV just a few feet underwater and still extract enough light for photosynthesis. But anything living on the surface could get fried without a liberal coating of Sunscreen 2000.
But we now have a glimmer of hope for red dwarf planets. Astrobiologist Antigona Segura of the Universidad Nacional Autónoma de México (UNAM) in Mexico City, simulated how a 1985 flare from the nearby red dwarf AD Leonis would have affected a hypothetical Earth-like planet orbiting a dwarf.