Sara Seager is Professor of Planetary Science and Physics at MIT, MacArthur Fellow (2013), and author of Exoplanet Atmospheres. She is leading development of two exoplanet telescope projects.

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We are one tool away from learning which distant planets already have life on them and which might be welcoming to life.

MIT Planetary Scientist Sara Seager is working on the tool. She is chair of the NASA team developing a “Starshade” that would allow a relatively rudimentary space telescope to observe Earth-size planets directly, which would yield atmospheric analysis, which would determine a planet’s life-worthiness.

Despite 1,000-plus exoplanet discoveries by the Kepler spacecraft and the hundreds more expected from the Transiting Exoplanet Survey Satellite after 2017, neither instrument can make detailed observation of the atmosphere of small rocky planets, because each star’s brilliance overwhelms direct study of the rocky motes that might harbor life. A Starshade cures that.

A former MacArthur Fellow, Seager is author of Exoplanet Atmospheres (02010) and an astrophysics professor at MIT. Her maxim: “For exoplanets, anything is possible under the laws of physics and chemistry.”

Photo by Justin Knight.

To find living exoplanets

Thanks to recent exoplanet research, Seager began, we now know that nearly all of our galaxy’s 300 billion stars are accompanied by planets, and a unexpectedly high number of them are rocky like Earth, and many of those orbit in a “habitable” range—meaning that they could harbor liquid water and perhaps life. How can we detect that life?

(To learn about the 4,700-plus planets so far discovered, Seager recommended an exciting dynamic map and encyclopedia from NASA called “Eyes on Exoplanets.” Seager predicts that “If an Earth 2.0 exists, we have the capability to find and identify it by the 2020s.”)

The way to discover life from a distance is to search for spectrographic evidence of “biosignature gases” such as oxygen or methane in the planetary atmosphere. To do that we have to acquire direct imaging of the rocky planets, but we can’t because our telescopes are blinded by the brilliance of the planet’s star, a billion times brighter than the planet. “It’s like looking for a firefly next to a searchlight, from thousands of miles away,” Seager said. Even the next planet-discovery telescope, called TESS (Transiting Exoplanet Survey Satellite), which is coming in 2018, will not be able to study exoplanet atmospheres.

The solution that Seager has been working on is called Starshade. To perfectly occult a star with a perfectly dark, hard-edged shadow, it will be deployed tens of thousands of kilometers from its telescope. It will be a disk 15 to 20 meters in diameter, with a perimeter of exotically shaped “petals” to defeat the effect of light diffracting around the edges of the disk. The edges have to be geometrically exact and machined to razor sharpness. The Starshade would fly in formation with a telescope located at the stable Lagrange point called L2, a million miles from Earth in the direction away from the Sun. The cost, including launch, will be about $650 million—not currently budgeted by NASA.

Now that we know planets are extremely common, one of the profoundest questions is whether life is also common in our galaxy, or is it extremely rare? Seager thinks that life abounds out there, and we will be able to point to examples in this century.