The Transiting Exoplanet Survey Satellite (TESS) is advancing the search for planets beyond our solar system, including those that may be capable of supporting life. The mission identifies exoplanets by detecting periodic dips in the brightness of their host stars, known as transits. TESS is set to survey 200,000 of the brightest stars near the Sun to find these transiting planets. The satellite launched on April 18, 2018, aboard a SpaceX Falcon 9 rocket.
TESS scientists anticipate the mission will identify thousands of potential exoplanets, significantly increasing the current count. Among these, around 300 are expected to be Earth-sized or super-Earth-sized planets, which are no more than twice the size of Earth. By focusing on planets orbiting the closest and brightest stars, TESS will provide future researchers with a valuable set of targets for further detailed studies.
Mission Approach
Over two years, TESS will systematically survey the entire sky, dividing it into 26 sectors measuring 24 degrees by 96 degrees each. The spacecraft's advanced cameras will observe each sector for at least 27 days, capturing data on the brightest stars at two-minute intervals. To put this into perspective, from Earth, the Moon appears half a degree in size—less than 1/9,000th the size of a single TESS sector.
The stars TESS will study are 30 to 100 times brighter than those observed by the Kepler and K2 missions, making follow-up observations much easier with both ground-based and space telescopes. Additionally, TESS will monitor a sky area 400 times larger than Kepler’s field of view.
Beyond searching for exoplanets, TESS will also support broader astrophysics research. Through its Guest Investigator program, scientists from various fields can request observations of up to 20,000 additional celestial objects during the mission.
The Transit Method
The transit method for detecting exoplanets works by observing small decreases in a star's brightness when a planet passes in front of it. This method requires the planet to be aligned with our line of sight to the star. Repeated, periodic dips in brightness indicate that a planet, or multiple planets, may be orbiting the star. Transit photometry, which measures the amount of light an object emits over time, provides valuable information about a planet. The amount of light a planet blocks helps determine its size. By measuring how long it takes the planet to complete one orbit, scientists can calculate the shape of its orbit and how long it takes to travel around its star.
Using this method, TESS will compile a catalog of thousands of potential exoplanets. Once the list is created, scientists will conduct follow-up observations using ground-based telescopes to confirm whether the detected objects are actual exoplanets or false positives. These telescopes will work together to determine the masses of these planets. By combining data on a planet’s size, orbit, and mass, researchers will be able to determine its composition. This will reveal whether the planets are rocky like Earth, gas giants like Jupiter, or something entirely different. Additional observations using both ground- and space-based telescopes, including NASA’s James Webb Space Telescope, will help scientists study the atmospheres of many of these planets.
TESS is a collaboration between several institutions, including the Massachusetts Institute of Technology, the Kavli Institute for Astrophysics and Space Research, NASA’s Goddard Space Flight Center, MIT’s Lincoln Laboratory, Orbital ATK, NASA’s Ames Research Center, the Harvard-Smithsonian Center for Astrophysics, and the Space Telescope Science Institute.
Mary Watson
