This question was asked on Reddits AMA: https://www.reddit.com/r/IAmA/comments/5vkoyd/were_nasa_scientists_exoplanet_experts_ask_us/de2vkvi https://www.reddit.

This question was asked on Reddits AMA: https://www.reddit.com/r/IAmA/comments/5vkoyd/were_nasa_scientists_exoplanet_experts_ask_us/de2vkvi https://www.reddit.com/r/IAmA/comments/5vkoyd/were_nasa_scie... 'The next generation of space telescopes, after WFIRST and JWST, to be launched in the 2030's. would be capable of actually getting a spectrum of the Earth, separate from the sun, using an instrument called a coronagraph or a star shade. The current telescopes could measure the size of the Earth as it transits in front of the sun. However, that only happens only once per year, so you have to know when to look, or look for a long time. The latter strategy was adopted by the original Kepler Mission. Michael Werner'