The Transiting Exoplanet Survey Satellite (TESS) is an upcoming NASA mission that will look for planets orbiting the brightest stars in Earth's sky. The mission will monitor at least 200,000 stars for signs of exoplanets, ranging from Earth-sized rocky worlds to huge gas giant planets. (TESS is slated to last two years, but if the mission is extended, it may look at more stars.)The mission will launch no earlier than April 16 from Cape Canaveral Air Force Station in Florida. Its launch vehicle will be a Falcon 9 rocket from SpaceX. From Earth, TESS will eventually make its way to a special orbit high above the planet, where it can perform observations with minimal interference from Earth's atmosphere.
"TESS anticipates the discovery of thousands of exoplanets of all sizes around a variety of star types," the Massachusetts Institute of Technology (MIT), which is leading the mission, said in a statement. Along with a network of ground telescopes that will verify TESS observations, the mission will find at least 50 planets that are close to Earth's size (no more than four times Earth's diameter).
"TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth," added a team led by TESS principal investigator George Ricker, who is an MIT astrophysicist, in a 2015 journal article about the mission.
"Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets," he added. "The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations."
Mission history and profile
TESS was first proposed in 2006 as a privately funded mission with financial backing from several institutions, including the Kavli Foundation, Google and donors at the Massachusetts Institute of Technology, according to NASA. It was eventually selected in 2013 as a mission in the Explorer program, which features large craft but do not exceed $200 million.
TESS will occupy a never-before-used orbit high above Earth, according to NASA. The elliptical orbit, called P/2, is exactly half of the moon's orbital period; this means that TESS will orbit Earth every 13.7 days. Its closest point to Earth (67,000 miles or 108,000 kilometers) is about triple the distance of geosynchronous orbit, where most communications satellites operate. When TESS reaches this point in its orbit, it will transmit data to ground stations; the process will take about three hours. Then TESS will pass through the Van Allen radiation belts to the highest point of its orbit, at 232,000 miles (373,000 km).
The solar-powered spacecraft carries four 100-millimeter-wide cameras that provide wide fields of view, according to NASA. They will stare at a particular region of the sky for between 27 and 351 days each, before moving on to another area. (The length of time will be decided according to where the region is in the sky, MIT stated.) The spacecraft is expected to map the Southern Hemisphere in its first year, and the Northern Hemisphere in its second year.
The satellite is a follow-up of NASA's highly successful Kepler space telescope, which has found thousands of exoplanets since its launch in 2009. TESS, however, will focus on stars that are 30 to 100 times brighter than those Kepler examined, NASA said. It's much easier for ground telescopes to follow up on observations if the stars are bright, and easy to spot. The discovered exoplanets will also be useful for the upcoming James Webb Space Telescope, which can examine them for more information for their atmosphere and composition after it launches in 2020.
Like Kepler, TESS will look at variations in the brightness of stars. If an exoplanet passes in front of a star (called a planetary transit), it blocks a portion of the light and causes the brightness to dip. The mission is expected to collect thousands of candidate exoplanets, including Earth-sized and "super-Earth sized" planets. This will help astronomers better understand the structure of solar systems outside of our Earth, and provide insights into how our own solar system formed.