The Fifth Annual Brilliant 10

Sara Seager, 35


Seeker, Distant Earths

Her simulations tell astronomers what fingerprints life may leave on other planets

In the past decade, astronomers have found 200 new planets orbiting distant stars, and not one of them looks like Earth. Sara Seager, an astronomer at the Carnegie Institution of Washington, thinks that´s set to change. Having devised a way to figure out what kind of atmosphere, if any, a far-off planet has, she´s trying to prove that planets like our own dot the Milky Way.

Since information about what distant planets are made of is scarce, Seager created her early models of extrasolar planets by considering what Earth must look like from thousands of light-years away. She then altered her "Earth" in a thousand different ways-doubling its size, or adding strange gases to the atmosphere-and recalculated its appearance each time. Her library of worlds not only reveals what newly
discovered planets might be made of, it also gives astronomers ideas for what to look for. "She is predicting things for which we have little or no experimental data," says San Francisco State University astronomer Debra Fischer, a member of the renowned team credited with discovering most of the known planets outside our solar system. "And those predictions drive all our observations."

In fact, Seager´s models helped in finding the first atmosphere around a distant planet. In 1999, just one month after Seager earned her Ph.D. from Harvard University, astronomers discovered a planet that passes in front of its parent star during every orbit as seen from Earth, blocking a small but detectable amount of starlight. Seager plugged what was known about the planet into her models and predicted that this Jupiter-like "gas giant" would have sodium and potassium in its atmosphere. Two years later, astronomers searched for and found these chemical "signatures."

Seager has since used her technique to chart the atmospheres around 12 worlds, and now she´s looking for chemical signatures like ozone, which could indicate Earth-like conditions and maybe even extraterrestrial life. She´s cataloguing every potential chemical that might be released by alien life and modeling what biosignatures each compound might leave in a planet´s atmo-
sphere. That way, when a telescope brings back those first signs of a living world, we´ll recognize it for what it is: another Earth.-Rena Marie Pacella