“The universe is teeming with planets,” and Jeremy Kasdin, an astronomer at Princeton University, wants to see them. Not in the way they’ve been detected so far, but directly. He wants to build a space telescope that will image a planet around another star and tell if it harbors life. There is probably one per star in the galaxy, and maybe 1/5 of those stars have an Earth-like planet around them. “But we haven’t seen any of them, we’ve only imaged them indirectly.”
He shows the famous image of the Pale Blue Dot, the image of Earth taken from 4 billion miles away by Voyager 1. That’s the kind of image that would tell us if there was life on other worlds. But it’s hard to do. To show why, Kasdin shows what a Hubble image of the Earth would look like from: the orbit of mars (pretty good), the orbit of Uranus (still good), at the edge of the solar system (barely resolvable), and by the nearest star, Alpha Centauri, where it is completely impossible to resolve because the light from the star (our sun) gets in the way.
The answer was worked out by Lyman Spitzer in 1952. He suggested that we take an inspiration from an eclipse. When the moon moves in front of the sun, we can see the faint corona around it. We could do this in space to block a star and see the planets in orbit.
There’s one problem, though. Light has a tendency to bend around screens, so too much light still gets through. Spitzer knew the answer to that as well: use a shaped screen. The design of his “starshade” looks like a flower, with many pointed petals. This controls the light in the right way to reduce the glare, down to levels where planets could be seen.
The design that they’ve come up with will use a screen about the size of half a football field that deploys 50,000 km away from a space telescope, sitting in exactly the right place to block the light of a star. It sounds like a formidable challenge, but his colleagues at JPL found a way to do it. (Watch an early animation.)
Kasdin and his colleagues have been working for several years on this. Last year they performed a test of a half-size starshade, each petal built by a summer intern, and it worked. 16 times. And every time it deployed correctly to within 1/10 of a millimeter. If this works in space, we could get direct images of planets beyond the solar system: “A family portrait of a solar system. Not our solar system, but someone else’s.”