Over the past few months, the search for habitable, Earth-like worlds orbiting other stars has begun to seem a lot less like finding a needle in a haystack. In January, Harvard-Smithsonian scientists estimated that about one in every six stars in the galaxy has an Earth-sized planet. A month later, colleagues reported that potentially-habitable worlds might be relatively close, astronomically speaking -- just 13 light-years away.
Last week, NASA announced that Massachusetts Institute of Technology scientists will lead a new $200 million mission to aid the search for such planets, called exoplanets, sending a refrigerator-sized telescope into orbit around the Earth in 2017. The spacecraft, called TESS, will be a powerful new tool for scientists, allowing them to scour hundreds of thousands of stars for signs of exoplanets of the right size, temperature, and distance from their suns to support life.
TESS, short for Transiting Exoplanet Survey Satellite, will use a technique that’s now standard, detecting the slight dimming that occurs as a planet travels around its sun and blocks a small fraction of the light seen by the telescope.
“TESS basically will look at half a million stars in the sky in two years,” said George Ricker, a senior research scientist at the Massachusetts Institute of Technology Kavli Institute for Astrophysics and Space Research. The telescope will be able to discern the size of the planets and how far they are from their stars, and determine whether they are good candidates for the search for second Earths. It will provide leads for a much more powerful telescope, the James Webb Space Telescope, to scrutinize more closely. That telescope, which will be launched in 2018, will be able to detect signs of water vapor or carbon dioxide in a planet’s atmosphere that could be indicative of life.
Ricker will oversee a team that includes other laboratories and companies that will contribute to the building of the spacecraft, design of the software, and data analysis. He answered a few questions about the mission in an interview.
Q: How is this different from other missions devoted to searching for Earth-like planets in the galaxy, such as the space-based Kepler and James Webb Space Telescopes?
A: James Webb is a large infrared telescope that has a very narrow field of view. Once you have a target, it can actually study the target in detail. But it can’t find targets on its own. So TESS is complementary to the James Webb Space Telescope, because it will identify the very best targets for potential study. ... The way to think about this is TESS serves the purpose of going out and scouting and identifying the very best targets for other missions, which have not yet been done to date.
Kepler is dedicated to studying this one location in the Milky Way in the constellation Cygnus very, very deeply. It’s trying to answer the question, for sun-like stars, what fraction of sun-like stars have planets that are essentially identical to the earth in orbits of about one year? It’s answering the question of how many, in a statistical sense. It’s a statistical mission. The purpose of TESS is to actually look in the full circle of the sky; we’re looking at 400 times [as much sky].
Q: Over the past few months, there have been different estimates of the frequency of Earth-like worlds around different types of stars. Will that influence TESS’s search?
A: When Kepler launched in 2009, there were less than 100 exoplanets actually known, and most of these were these giant, Jupiter-sized planets that were orbiting extremely close to their host stars, so the temperatures were thousands of degrees and they weren’t in any way similar to the type of place you’d want for life. Then, Kepler found a lot of smaller planets, but the problem with the small planets that Kepler found is that the Kepler stars are so far away [from Earth] -- 10 to 20 times farther away than the planets TESS will find.
Kepler looks at 160,000 to 170,000 stars; TESS will look at more than half a milllion stars. We’ve known from Kepler that it would be good to concentrate on smaller stars, which are these cool, so-called M-dwarf or red dwarf stars. And we’re going to look at every single one that anyone knows of in the entire sky. In addition, we’ll be able to look at another several hundred thousand that might be interesting. The thing that Kepler was able to do is give us the odds, for any given star type, that it would have a planet. But it didn’t tell you which ones had planets.
Q: How will TESS aid the James Webb Space Telescope search?
A: The thing that it does do, and I’m sure the NASA people thought about, is that for an [approximately] additional 2 percent investment, by funding TESS, they can greatly improve the productivity that the James Webb Space Telescope will have. And in fact, people have argued that it could certainly improve the productivity of James Webb Space Telescope in this area by 100 percent, because it’s a huge difference. Right now, until TESS flies, we will not know more than one to two candidates [for habitable, Earth-like worlds].