NASA's new planet-hunter TESS switched on

The number of planets we know about is set to explode.

NASA's newest planet-hunting satellite, TESS, has just been switched on after 12 years of planning.

Short for Transiting Exoplanet Survey Satellite, TESS will be able to look at an area of the sky 400 times larger than Kepler.

"I'm thrilled that our new planet hunter mission is ready to start scouring our solar system's neighbourhood for new worlds," said Paul Hertz, NASA Astrophysics division director.

"Now that we know there are more planets than stars in our universe, I look forward to the strange, fantastic worlds we're bound to discover."

Kepler, launched in 2009, has so far found more than 2600 confirmed exoplanets orbiting other stars. It's still operating, despite a mechanical failure in 2013 that nearly ended its mission.

TESS will be able to spot smaller planets than Kepler, around much closer stars. It's expected to find at least 20,000 of them, including between 500 and 1000 rocky planets similar to Earth.

 Once they've been found by TESS, astronomers hope the upcoming James Webb Space Telescope will be able to figure out whether they have atmospheres capable of supporting life. James Webb has been in the planning since the mid-1990s, but isn't expected to launch until 2021 at the earliest.

TESS launched in April aboard a SpaceX Falcon rocket. It circles the Earth in an elliptical orbit every 13.65 days - twice as fast as the moon.