Alien Life-Seekers Have New Reason To Hope

Eager to identify other candidate Gaias, astronomers have high hopes for the Kepler spacecraft to be launched in February. Kepler will take a different approach in its planetary scan, Dr. Seager said, searching not for stellar wobbles but for “tiny drops in brightness,” possible signs of a planet transiting across the distant Sun’s face. Kepler will track 100,000 stars for four years, enough to detect the occasional crossing of any planets with leisurely orbits like ours. “It will be akin to the great age of exploration, the explorers of the 16th century,” Dr. Shostak said. “We will nail down what fraction of stars have planets,” and more important, “what fraction of those planets are small, terrestrial planets.” With that comprehensive planetary atlas in hand, we can pick out the places most worthy of follow-up probes: planets that are relatively close, and closest in kind to the one we know best. We can look for rocky planets that follow stable paths, and are laced with clouds of water vapor that hint at liquid oceans below, and, can it be, atmospheric oxygen, the voice of a biosphere. “Oxygen is so reactive that it shouldn’t be in the atmosphere unless it’s being produced by something like photosynthesis,” Dr. Seager said. “It’s a huge indicator of life.”