NASA’s Kepler space telescope has ended its planet spotting mission, but the agency’s Transiting Exoplanet Survey Satellite (TESS) has already picked up the torch. TESS has detected a new exoplanet called HD 21749c. This is not the first planet to show up in TESS data, but it is the first Earth-sized planet.
TESS launched in April 2018 atop a Falcon 9 rocket. The Kepler telescope was already experiencing issues due to mechanical failures at that time, but it had already far surpassed expectations by spotting thousands of potential exoplanets. TESS started science operations in July 2018, several months before NASA announced Kepler was out of fuel and would shut down. Since then, TESS has several exoplanets including a “hot Jupiter” 480 light years away and a super-Earth orbiting Pi Mensae 60 light years distant.
The newly identified exoplanet is 52 light years away, orbiting a star called HD 21749. There are actually two planets in that solar system (and maybe more we haven’t discovered yet). The larger is HD 21749b, a “sub-Neptune” large planet with a 36-day orbit that researchers announced back in January. HD 21749c is roughly the size of Earth and orbits the star in just 7.8 Earth days.
While HD 21749c is the size of Earth, it’s almost undoubtedly inhospitable to life as we know it. With its tight orbit, the surface temperature on HD 21749c is probably in excess of 800 degrees Fahrenheit (426 degrees Celsius). Still, this is an important milestone for TESS, with which NASA hopes to catalog at least 50 Earth-like planets during its two-year mission.
TESS has an array of four highly sensitive cameras that take an image every two seconds. Scientists then watch for repeating dips in luminance from distant stars, indicating planets are transiting in front of them. This is an effective way to detect distant objects, but it only works on solar systems that are properly aligned with our own.
Over the course of its mission, TESS will scan the entire sky and return data on about 500,000 stars. The observed area will be about 400 times larger than Kepler, but TESS won’t see exoplanets as far away. Scientists expect most detections to be within 300 light years. However, scientists will be able to gather more data on those planets like mass and atmospheric composition because of their relative nearness. To get a closer look, we’ll have to wait on the James Webb Space Telescope, which is currently slated for 2021 launch.