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TESS takes off

A spacecraft the size of a refrigerator could help find habitable planets.
June 27, 2018

More than a decade ago, a team of MIT scientists led by George Ricker proposed sending cameras to space to identify the thousands of planets suspected to lie just outside our solar system—galactic neighbors that could be rocky worlds or more tenuous collections of gas and dust. In April, the Transiting Exoplanet Survey Satellite (TESS), a NASA-funded spacecraft not much larger than a refrigerator, launched from Cape Canaveral to do just that, carrying four cameras that were conceived, designed, and built at MIT’s Kavli Institute for Astrophysics and Space Research and Lincoln Laboratory.   

Following a novel “lunar-resonant” orbit that will keep it extremely stable, TESS will spend two years scanning nearly the entire sky—a field of view that can encompass more than 20 million stars. Scientists expect that thousands of these stars will turn out to be orbited by planets, which they hope to detect using TESS’s cameras. 

Amid this extrasolar bounty, the TESS science team at MIT aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth. Many of the planets identified should be close enough for scientists to study with other telescopes in an effort to detect atmospheres, characterize atmospheric conditions, and even look for signs of habitability.

“We’re on this scenic tour of the whole sky,” says Natalia Guerrero, deputy manager of TESS Objects of Interest, an MIT-led effort that will catalogue objects identified through TESS data with an eye toward finding potential exoplanets. “It’s like we’re making a treasure map: Here are all these cool things. Now go after them.”

As TESS collects and downlinks images of the sky, scientists at MIT and NASA will convert the raw data into light curves that indicate the changing brightness of a star over time. Then the TESS Science Team, including Sara Seager, professor of earth, atmospheric, and planetary sciences and deputy director of science for TESS, will look through thousands of light curves for at least two similar dips in starlight, indicating that a planet may have passed twice in front of its star. The researchers will then employ a battery of methods to determine the mass of a potential planet.

“If you just know that a planet is twice the size of Earth, it could be a lot of things: a rocky world with a thin atmosphere, or what we call a ‘mini-Neptune’—a rocky world with a giant gas envelope, where it would be a huge greenhouse blanket and there would be no life on the surface,” Seager says. “So mass and size together give us an average planet density, which tells us a huge amount about what the planet is.”

The team will make TESS data publicly available for anyone to download and interpret, including high school students, armchair astronomers, and other research institutions.

With so many eyes on TESS’s data, Seager says, there’s a chance that someday a nearby planet discovered this way might be found to have signs of life. 

“There’s no science that will tell us life is out there right now,” Seager says. But small rocky planets “appear to be everywhere we look,” she adds. “So it’s got to be there somewhere.” 

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