The glare from other stars has made it impossible to image their planets—blocking out the light could make it possible to study them directly.
Over the last five years, NASA’s Kepler Space Telescope has found dozens of potentially habitable planets. The only problem is that we can’t actually see them, because the glare from those planets’ stars makes it impossible to image them directly. A new, audacious plan to completely block out the light from those stars, however, could change all of that.
It’s called Starshade, and, given the name, it works exactly how you might expect it to. If you look directly at the sun, you're not going to be able to see anything in the sky around it. Hold up something between your eyes and the sun to block it, however, and you'll be able to see much better.
The plan calls for a satellite to be sent out several tens of thousands of miles from Earth. The satellite will unfold a huge, flower-shaped metal shade that will literally block the light of some far-out star to the point where a space telescope, which will directly communicate with Starshade, will be able to image whatever planets are orbiting it directly.
One of Starshade's petals. Image: Jason Koebler
“It’s kind of like asking a friend to hold up a dime five miles away and precisely block something out,” Sara Seager, an MIT researcher who is helping design the project, said at Smithsonian Magazine's The Future is Here event in Washington, DC this weekend. “The petals of the shade have to be precisely made—we have to have it travel far away from the telescope to block the starlight out to reveal any planets present.”
Seager showed off one of the shade's "petals" at the event. The finished satellite will have dozens of them that can unfurl in a specific pattern so as to completely block the light from a star. It'll look like this:
Though Kepler has found thousands of planets, it’s an indirect way of studying them. Basically, the telescope (before it was broken), pointed at a bunch of far off stars and waited for a planet to transit between the star and Kepler's eye.
With that information, scientists could estimate how far away the planet was from its star, its mass, and its circumference—all useful data points, but ones that only tell us if a planet is roughly similar to Earth or not. We learn nothing about what it looks like (despite many artists’ representations of those planets), nothing about its atmosphere, and nothing about the planet’s makeup.
We have space telescopes strong enough to image these planets, but Seager says that, often, stars can be as many as “10 billion times as bright” as its planets—making them completely impossible to see without blocking out the star.
Already, Seager’s team is working with NASA to create a prototype—they plan on testing the mission sometime in 2017, with a full launch tentatively scheduled for 2022. She says that if they can do it for “anything under a billion dollars” it’ll be considered a success. If it works, the amount of information we can get about any given planet will be far beyond what we’ve been able to get with Kepler.
“We can look for greenhouse gases, measure its temperature and see if there are any gases that could have been created by life as we know it,” she said.
Of course, every star is different, and the Starshade has to both be precisely made and perfectly positioned for a telescope to actually be able to see anything. But launching a billion dollar satellite into space to look at exoplanets around just one star makes no sense, Seager said. So the Starshade has to be reconfigurable and repositionable. The team expects that it’ll be able to aim at a new star every 10 days or so.
“We can only point it at one star at a time, but it’s absolutely important that we reposition it,” she told me. “We’ll be able to move the telescope across the sky or we can move the Starshade.”
Kepler, so far, has given us an idea of where to look. Seager said that the plan is to use Starshade to fill in the missing pieces, so, eventually, humans will know where to meet other life. In fact, the team already has a list of a couple dozen planets and star systems that it'd first like to image.
“To the rest of the universe, our Earth is just another exoplanet,” she said. “We think our descendants might get to another planet around another star—we’re going to use these findings to give give them the map of places they might go.”