NASA's new planet hunter TESS to scan sky for alien worlds

KENNEDY SPACE CENTER, Fla. – The search for cosmic real estate is about to begin anew.

No earlier than April 16, in NASA's parlance, a little spacecraft known as the Transiting Exoplanet Survey Satellite, or TESS, bristling with cameras and ambition, will ascend on a SpaceX Falcon 9 rocket and take up a lengthy residence between the moon and Earth.

There it will spend the next two years, at least, scanning the sky for alien worlds.

TESS is the latest effort to try to answer questions that have intrigued humans for millenniums: Are we alone? Are there other Earths? Evidence of even a single microbe anywhere else in the galaxy would rock science.

Not so long ago, astronomers didn't know whether there were planets outside our solar system. But starting with the 1995 discovery of a planet circling the sunlike star 51 Pegasi, there has been a revolution.

NASA's Kepler, launched in 2009, discovered 4,000 possible planets in one small patch of the Milky Way near the constellation Cygnus. Kepler went on to briefly survey other star fields, but it's running out of fuel after nine years in space.

Thanks to efforts like Kepler's, astronomers now think there are billions of potentially habitable planets in our galaxy, which means the nearest one could be as close as 10 to 15 light-years from here.

And so the torch is passed. It's now TESS' job to find those nearby planets, the ones close enough to scrutinize with telescopes, or even for an interstellar robot to visit.

"Most of the stars with planets are far away," said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology and a member of the TESS team, referring to Kepler's bounty. "TESS will fill in planets around nearby stars."

George Ricker, an MIT researcher and the leader of the TESS team, expects to find some 500 Earth-size planets within 300 light-years, close enough for a coming generation of telescopes to examine for habitability — or perhaps even inhabitants.

Mission planners say they expect to catalog 20,000 new exoplanet candidates of all shapes and sizes. In particular, they have promised to come up with the masses and orbits of 50 new planets that are less than four times the size of the Earth.

Most of the planets in the universe are in this range — between the sizes of Earth and Neptune. But since there are no examples of them in our own solar system, as Seager notes, "we don't know anything about them."

TESS is one of NASA's smaller missions, with a budget of $200 million; Kepler had a budget of about $650 million.

To start its adventure, TESS will be launched into an unusually eccentric orbit that takes the satellite all the way out to the moon at its farthest point. Gravitational interaction with the moon will then keep TESS in a stable 13.7-day orbit for as long as 1,000 years, Ricker said.

But it will take almost two months and many rocket burns to get there and begin to do science. If all goes well, that would be the middle of June.