Will the next generation of ground-based telescopes be able to detect Earth-like planets? What kind of details would they be able to reveal? What will OWL find?
OWL (the Overwhelmingly Large Telescope) was supposed to be a huge telescope with a diameter of about 100 m, and was supposed to operate in the visible and infrared. It has been canceled, but the European Southern Observatory is still planning on going ahead with the European Extremely Large Telescope (E-ELT), which may discover some new small planets.
The vast majority of planets so far detected come from the Kepler Observatory using the transit method. This is where we measure the light of host stars to very high precision to look for planets that cross in front of their host stars and block light with every orbit. The transit method can successfully be performed on large swaths of the sky and to detect lots of planets. The Kepler Observatory has been the most successful of all methods at finding small rocky planets This catalog keeps a list of ones that may have liquid water on their surfaces:
The next generation of giant ground based telescopes: the E-ELT (39m), GMT (25m), and TMT (30m) are all exiting new observatories that will teach us new things about Galaxies to Jupiters to Earth-like planets. These observatories are equipped with cameras that can find Earth-like planets, but it is likely they will be used to study planets already known such as found by the Kepler Observatory or TESS. It is difficult to say exactly what the best use of the observatories will be 10 years down the road, but they can tell us everything from the mass of these planets to what are the constituents of their atmospheres to the global wind speeds.
Updated by Everett Schlawin on July 18, 2015.