Seeking Signs of Life
Young faculty shaping the future
If your research focus is planets outside the solar system, it might not hurt to have a reasonably high tolerance for risk. Consider the experience of Sara Seager, now the Ellen Swallow Richards Associate Professor of Planetary Sciences at MIT. A math-physics whiz with an intense interest in astronomy as a kid, Seager studied both math and physics in college. But it was when she later started graduate work at Harvard that the first reports of what are now called exoplanets began appearing.
The documentation in those initial reports was sketchy enough that some felt they might reflect some type of odd astronomical quirk, not actual planets. Seager’s Ph.D. thesis was about how mathematical modeling techniques could generate key information about exoplanets, and she says, “some people thought the claims made in my thesis would never be substantiated.” But exoplanets kept turning up — the count is currently 250 and rising — and Seager’s work was validated.
Exoplanets are usually found thanks to a minuscule “wobble” in a star’s course. Most exoplanets found to date, for reasons generally having to do with the size of the wobble they cause, are Jupiter-like: very large, and gaseous. Most also orbit near their stars. But her interests go beyond those inevitably super-hot planets. “Our goal,” she says, “is to find planets that are potentially habitable.”
What that basically means is Earth-like. This doesn’t imply they must be Earth sized, or have the same length year. But they should be solid, and almost certainly should have significant atmospheres. Moreover, says Seager, “they should have liquid water on their surfaces.”
The problem for seekers of exoplanets in general is that a vanishingly small amount of radiation reaches Earth from the stars under scrutiny, much less their planets, making it hard to get more than the most basic data about the planets. But that’s where modelers like Seager can help.
Seager, for example, set the stage for the first discovery of an exoplanetary atmosphere. “My models said that if one specific, hot planet had an atmosphere, it should contain sodium,” she says. An observing group that went looking for sodium’s signature in the radiation from the planet soon found it.
The problem of limited data, of course, is especially acute for the exoplanets most likely to harbor life. They’re likely to be smaller than most known exoplanets, and further from their stars, hence tough to find or analyze. But new satellite telescopes — among them one being designed by a group that includes Seager — will boost the odds. And because there are probably millions of stars in the Milky Way Galaxy that merit canvassing, the chances of eventual success seem good.
“I believe there are exoplanets with life on them,” says Seager, also a member of the physics department. “Unfortunately, it’s not clear we’ll ever be able to say unambiguously that they harbor life.”
Proof is likely to require on-site sampling. And if an exoplanet is 20 light years away — not a lengthy distance in exoplanetary terms — a ship traveling one-tenth the speed of light would take 200 years to arrive, and another 20 to beam any findings back to Earth.
Still, Seager has no regrets about choosing work whose ultimate goal may never be realized. “Relatively few people get to do exactly what they want to do,” she says, “and I’m one of them.”