There are potentially thousands of planets that lie just outside our solar system — galactic neighbours that could be rocky worlds or more tenuous collections of gas and dust. Where are these closest exoplanets located? And which of them might we be able to probe for clues to their composition and even habitability? The Transiting Exoplanet Survey Satellite (TESS) will be the first to seek out these nearby worlds.
The NASA-funded spacecraft, not much larger than a refrigerator, carries four cameras that were conceived, designed, and built at MIT, with one wide-eyed vision: to survey the nearest, brightest stars in the sky for signs of passing planets.
Now, more than a decade since MIT scientists first proposed the mission, TESS is about to get off the ground. The spacecraft is scheduled to launch on a SpaceX Falcon 9 rocket from Cape Canaveral Air Force Station in Florida, no earlier than the 16th April, at 6:32 p.m. EDT.
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 host transiting planets, which they hope to detect through images taken with 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 TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterise atmospheric conditions, and even look for signs of habitability.
“TESS is kind of like a scout,” says Natalia Guerrero, deputy manager of TESS Objects of Interest, an MIT-led effort that will catalog objects captured in TESS data that may be potential exoplanets.
“We’re on this scenic tour of the whole sky, and in some ways we have no idea what we will see,” Guerrero says. “It’s like we’re making a treasure map: Here are all these cool things. Now, go after them.”
TESS’s origins arose from an even smaller satellite that was designed and built by MIT and launched into space by NASA on Oct. 9, 2000. The High Energy Transient Explorer 2, or HETE-2, orbited Earth for seven years, on a mission to detect and localise gamma-ray bursts — high-energy explosions that emit massive, fleeting bursts of gamma and X-rays.
To detect such extreme, short-lived phenomena, scientists at MIT, led by principal investigator George Ricker, integrated into the satellite a suite of optical and X-ray cameras outfitted with CCDs, or charge-coupled devices, designed to record intensities and positions of light in an electronic format.
“With the advent of CCDs in the 1970s, you had this fantastic device … which made a lot of things easier for astronomers,” says HETE-2 team member Joel Villasenor, who is now also instrument scientist for TESS. “You just sum up all the pixels on a CCD, which gives you the intensity, or magnitude, of light. So CCDs really broke things open for astronomy.”
In 2004, Ricker and the HETE-2 team wondered whether the satellite’s optical cameras could pick out other objects in the sky that had begun to attract the astronomy community: exoplanets.
Around this time, fewer than 200 planets outside our solar system had been discovered. A few of these were found with a technique known as the transit method, which involves looking for periodic dips in the light from certain stars, which may signal a planet passing in front of the star.
“We were thinking, was the photometry of HETE-2’s cameras sufficient so that we could point to a part of the sky and detect one of these dips? Needless to say, it didn’t exactly work,” Villasenor recalls. “But that was sort of the seed that started us thinking, maybe we should try to fly CCDs with a camera to try and detect these things.”
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Image credit: MIT.