Scientists with MIT's TESS project hope to build on the lessons of the successful Kepler planet-hunting mission and find planetary systems close enough for telescopes to study in detail.
Relative sizes of Kepler habitable zone planets discovered as of April 18, 2013, in this artist's rendition provided by NASA. Scientists using NASA's Kepler space telescope have found the best candidates yet for habitable worlds beyond the solar system.
NASA Amers/JPL-Caltech/REUTERS
EnlargeThe discovery of three new super-Earths by scientists with NASA's Kepler mission is helping to reveal the bounty of extrasolar planets across the Milky Way.
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Now another team is set to build a new orbiting planet hunter that, during a two-year mission, will search for other worlds closer to our sun's neighborhood.
The Transiting Exoplanet Survey Satellite (TESS), which NASA approved under its Explorer program earlier this month, will be the first orbiting observatory to hunt for planets all around the sky.
NASA and the project's scientists, led by George Ricker of the Kavli Institute for Astrophysics and Space Science at the Massachusetts Institute of Technology in Cambridge, Mass., aim to launch the observatory in April 2017.
In essence, TESS?hopes to build on Kepler's pioneering role as an extrasolar-planet census taker and bring that nose count closer to home, where existing and future ground- and space-based telescopes can study in detail the planetary systems TESS uncovers.
Such studies "will allow us to really begin to figure out what their atmospheres are made of, what the temperature is like ? actually characterize those planets," says Doug Hudgins, project scientist for Kepler and TESS at NASA headquarters in Washington.
This kind of analysis not only will help astronomers uncover the range of solar system configurations and test ideas on how planets form and evolve. Such up-close looks also could provide evidence for life on any of the newly discovered worlds.
Among the signs researchers might look for: the presence of ozone ? a molecule made of three oxygen atoms ? and nitrogen oxides in a planet's atmosphere. On Earth, fossil evidence indicates that the first algae capable of photosynthesis, which produces oxygen, emerged some 3.5 billion years ago. On Earth, bacteria also produce copious amounts of nitrogen oxides.
The hunt for signs of life elsewhere in the galaxy is one of the drivers behind Kepler, and the inspiration for TESS. But Kepler isn't looking directly for life. Instead, it is looking for Earth-mass planets orbiting at Earth-like distances around sunlike stars in order to provide an estimate of how common such planets are.
On Thursday, Kepler's science team announced the discovery of three super-Earths in or on the boundary of their stars' habitable zones. The habitable zone is a region around the star far enough away so that a planet doesn't overheat, but close enough so it doesn't freeze either. In principle, a planet orbiting in its star's habitable zone should be able to host liquid water in stable quantities on its surface. Liquid water is seen as essential for organic life.
But the nearest of these new systems is 1,200 light-years away. Although the team speculates that one of the two super-Earths there is a water world and the other likely has a rocky surface, and while both fall into their star's habitable zone, they are too far away and their star is too dim to study with anything more than computer models.
TESS's targets should fall well within the gaze of a new generation of ground- and space-based telescopes. But those telescopes need to know where to look, Dr. Hudgins notes. And that's where TESS comes in.
Like Kepler, TESS is designed to detect planets as they pass in front of their host stars, dimming the starlight by a tiny fraction. If one could look back at the sun from beyond the solar system and watch for the wink an orbiting Earth would impart, the light would vary by just 0.000085 percent, a no-see-um in human terms.
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