Two technologies to help find other Earths

Scientists and engineers are actively working on two technologies to help with this challenge: the starshade, a giant flower-shaped spacecraft; and coronagraphs, single instruments that fit inside telescopes. Both a starshade and a coronagraph block the light of a star, making it easier for telescopes to pick up the dim light that reflects off planets. This would enable astronomers to take pictures of Earth-like worlds -- and then use other instruments called spectrometers to search the planets' atmospheres for chemical clues about whether life might exist there.

"Coronagraphs are like visors in your car -- you use them to block the light of the sun so you can see the road," said Nick Siegler, the program chief technologist for NASA's Exoplanet Exploration Program Office at JPL. "Starshades, on the other hand, are separate spacecraft that fly in front of other telescopes, so they are more like driving behind a big truck in front of you to block the light of the sun." Siegler is featured in the Crazy Engineering video.

The starshade would be a large structure about the size of a baseball diamond that deploys in space and flies in front of a space telescope. The spacecraft, which looks like a giant sunflower would be used to acquire images of Earth-like rocky planets around nearby stars. Rocky planets with just the right temperature for liquid water -- not too hot, not too cold -- could be possible abodes for life outside our solar system. NASA's Kepler mission has discovered hundreds of planets orbiting other stars, called exoplanets, some of which are a bit larger than Earth and lie in this comfortable "Goldilocks" zone.

Researchers generally think it's only a matter of time before we find perfect twins of Earth. The next step would be to image and characterize their spectra, or chemical signatures, which provide clear clues about whether those worlds could support life. The starshade is designed to help take those pictures of planets by blocking out the overwhelmingly bright light of their stars. Simply put, the starshade is analogous to holding your hand up to the sun to block it while taking a picture of somebody.

Coronagraphs, which use tiny masks to block the light of stars from within a telescope, are also currently in development at JPL, as part of NASA's Wide-Field Infrared Survey Telescope, or WFIRST, mission, led by NASA's Goddard Space Flight Centre in Greenbelt, Maryland. Coronagraphs are instruments introduced in the early 20th century to study our sun. They use special masks to block out light from the circular disk of the sun, so that scientists can study its outer atmosphere, or corona.

NASA is developing more sophisticated coronagraphs to block the glaring light of other stars and reveal faint planets that might be orbiting them. Stars far outshine their planets; for example, our sun is 10bn times brighter than Earth. That's similar to the flood of football stadium lights next to a tiny candle.

Telescopes on the ground have already used coronagraphs to take pictures of planets, but those planets are easier to photograph because they are large, bright, and orbit far from their host stars. To take a picture of Earth-size planets lying in the habitable zone of sun-like stars -- the region where temperatures are just right for possible liquid oceans and lakes -- will require a telescope in space. Out in space, the blurring effects of our blustery atmosphere can be avoided.

A JPL "Crazy Engineering" video visits both technologies at NASA's Jet Propulsion Laboratory in Pasadena, California.