In March 2018, if all goes as planned, a SpaceX Falcon 9 rocket will send an instrument designed and fabricated at MIT, the Transiting Exoplanet Survey Satellite (TESS), into high Earth orbit. From an altitude of about 400,000 kilometers, TESS will conduct an all-sky survey that brings a new perspective to the search for planets beyond our solar system.

On the fourth floor of MIT’s Building 37, a dozen computers working in parallel will process data relayed from the orbital satellite, and about 30 MIT scientists and engineers will pore over it for clues about our astronomical neighborhood. “MIT has the overall technical and science responsibility for the mission,” says TESS principal investigator George Ricker ’66, PhD ’71, a senior research scientist at the MIT Kavli Institute for Astrophysics and Space Research. Fellow Kavli scientist Roland Vanderspek PhD ’86 serves as deputy PI. Altogether about 300 researchers from more than a dozen universities and other institutes are taking part in this NASA Explorer mission. TESS’s unique capabilities should enable it to pick out small, relatively nearby planets (within a few hundred light-years of Earth) that offer at least some of the conditions deemed necessary for life. The ambitious endeavor could give humanity its best shot yet at understanding just how unusual our planet is, or isn’t, in the grand scheme of things.

To fulfill its scientific objectives, TESS will rely on the “transit method,” looking for periodic dips in a star’s brightness that could be caused by an orbiting planet passing in front of it. “If you know the star’s size, you can figure out the planet’s size from the percentage of light that’s being blocked,” Ricker explains.

That task falls to the satellite’s four CCD cameras—precise photometers fabricated at MIT Lincoln Lab and on campus under the watchful eye of instrument manager Greg Berthiaume ’86. Vanderspek, meanwhile, is responsible for achieving the requisite stability and sensitivity of those cameras, charged with surveying 90% of the southern sky in TESS’s first year of operation and a similar portion of the northern sky a year later. Ricker estimates this will turn up approximately 3,000 “transit signals,” or instances of temporary dimming, of which 1,700 might be confirmed as planets by ground observations in the third year.

Leading the TESS science team are Harvard-Smithsonian astronomer David Latham ’61 and Sara Seager, MIT’s Class of 1941 Professor of Planetary Science and Professor of Physics, as well as an AeroAstro faculty member. Joined by new MIT physics assistant professor Ian Crossfield, they will select 100 candidates for follow-up observations, whittling that down to a list of at least 50 confirmed small planets, roughly Earth-sized, a subset orbiting within the host star’s “habitable zone” at a distance where surface water could exist in liquid form. The Hubble Space Telescope and successors like the James Webb Space Telescope would then train their sights on the exoplanetary “Top 50,” as would large ground-based telescopes. “We’ll definitely want to look at their atmospheres to check for the presence of gases—such as oxygen, water vapor, and methane—that may be associated with life,” says Seager.

TESS will complement NASA’s Kepler mission, which has already discovered more than 2,000 confirmed exoplanets within a small patch of sky. With its broader sky coverage, TESS can find planets about 10 times closer, circling much brighter stars, making it easier to determine their mass, density, composition, and other properties.

TESS joins other exoplanetary research underway at MIT. Julien de Wit PhD ’14, a postdoc in the Department of Earth, Atmospheric and Planetary Sciences who recently accepted an offer to join the MIT faculty, is part of an international team that spotted seven Earth-sized planets orbiting the star TRAPPIST-1. Seager, meanwhile, is the principal investigator of ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics), a low-cost mission that’s set to launch a cereal box-sized satellite this year in the hopes of finding the best Earth analog yet. Says Seager, “We’re following any leads we can to learn more about exoplanets.”

At the same time, perhaps, sentient creatures on one of those worlds might be going through a similar exercise, trying to learn about Earth and its curious inhabitants.

Steve Nadis is a 1997–98 MIT Knight Science Journalism Fellow.


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