In a recent Big Think interview, theoretical physicist Dr. Michio Kaku described the search for Earth's twin as the "Holy Grail of planetary astronomy." In the case of other potentially habitable planets, the next step after discovery, according to Kaku, is for scientists to "discern if we can find out what their atmospheres are like. Do they have oxygen? Do they have H2O?" Then send in SETI with their eavesdropping devices to "see if there are any radio emissions from intelligent beings on these planets."