Sara Seager : The Planet seeker

Hundreds of years from now, says Sara Seager, “people will look back at us, and they won’t remember me or you. They’ll remember us as the generation of people who first found the Earth-like worlds” outside our Solar System.

This year, scientists have come tantalizingly close, says Seager, an astronomer at the Massachusetts Institute of Tech- nology (MIT) in Cambridge. NASA’s Kepler space telescope, which monitors thousands of stars for dimming caused by an orbiting planet, has found 28 confirmed exoplanets this year, including one that is slightly bigger than Earth and in
its star’s habitable zone. More than 2,000 await verification. But Seager, a member of the Kepler science team, wants to do better.

Kepler can reveal a planet’s size and orbital radius, she explains. But to find out whether such a planet is Earth- like — with free oxygen or other signs of biological activity in its atmosphere — astronomers need a spectrum of the parent star’s light reflected from or transmitted through the atmoshere. Because the stars in Kepler’s field of view are up to 920 parsecs (3,000 light years) away, they are too dim for that. Seager wants to search for Earth-like planets no more than 30 parsecs away, close enough that their atmospheres could be studied. Her tool would be a 10 × 10 × 30-centimetre space telescope designed to watch a single star for a planetary transit. Such an ‘ExoplanetSat’ would not be able to analyse spectra by itself. For that, Seager will need an orbiting telescope such as the Terrestrial Planet Finder, an ambitious concept that NASA put on ice in 2006. But a fleet of ExoplanetSats could provide a resurrected planet finder with a map of where to look. Each ExoplanetSat would cost less than US$1 million. Rather than a telescope mirror, it would rely on a modified, $1,300 commercial lens. And dozens could be launched very cheaply, piggybacking on rockets carrying other missions.

“I’m trying to do new things,” says Seager, who is teaching herself the necessary engineering and is aiming for a 2013 launch. Her group has received roughly $3 million in funding from MIT, Draper Laboratory in Cambridge and elsewhere.

Geoff Marcy, an astronomer at the University of California, Berkeley, and one of the first exoplanet seekers, lauds Seager’s creativity in unfamiliar fields. “There are thousands of scientists working on exoplanets,” he says. “She’s looking for something different.”

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