But we can accomplish identifying an inhabited planet by 2020 if we get very lucky in finding a big planet orbiting a small nearby star, according to an article in NATURE magazine published last month by MIT's Sara Seager and Drake Deming of NASA's Goddard Space flight Center. Seager describes how to go find another Earth in a nicely illustrated, concise book she has published online called "Is There Life Out There? The Search For Habitable Exoplanets."
A small star is dim, and a planet bigger than Earth is easier to detect. There are more than 10,000 red dwarf (M-class) stars within 100 light-years of Earth. It's predicted that a handful of these will have super-Earths that (1) lie very close to the star in its habitable zone and (2)
transit the star so that diameter and density can be calculated. The atmosphere can also be measured during a transit, as Hubble successfully demonstrated in 2002.
The James Webb Space Telescope (JWST) scheduled for launch in 2014, has the potential to find an inhabited planet. This would be possible if a free-flying "starshade" were placed 9,300 miles behind Webb, it could block out the star's light and allow for reflected light from the planet to be collected.