EXOPLANET SCIENTISTS EXPERIENCED A HANDOFF IN THE RACE TO FIND HABITABLE PLANETS ON APRIL 18, when NASA’s new exoplanet hunter, the Transiting Exoplanet Survey Satellite (TESS), launched. Three months later, TESS began science operations as the previous exoplanet-search workhorse, the Kepler space telescope, went into safe mode due to low fuel. And on October 30, NASA officially ended the nearly 10-year-long mission, retiring the telescope.

From planets around binary stars to systems hosting multiple small worlds, Kepler’s discoveries are the foundation upon which every exoplanet search in the future will be built. And TESS is the first to follow. Both telescopes use the same detection method: watching for periodic dips in starlight, which indicate an orbiting planet passing in front of its host star and blocking its light. But the types of stars they watch are very different. “Kepler was a pencil-beam survey during the main mission,” says University of California, Berkeley, astronomer Courtney Dressing. Initially, Kepler watched the same 100° star field for several years and detected worlds with many different orbital periods — the longest taking more than three and a half years to orbit their stars. But most of the stars Kepler studied are far away, and therefore dim. Faint light means it’s hard to see the details that allow astronomers to measure characteristics such as a planet’s mass. TESS’ catalog of brighter stars will be easier to follow up on from the ground. TESS will find worlds orbiting red dwarf stars in our nearby neighborhood, astronomically speaking. It will also scour almost the entire sky in its initial two-year mission, spending 27 days on each portion. “To be sure that we’ve found a real planet, we like to see it transit many times,” adds Dressing. “That means that many of TESS’ planets will be very close to the star and go around once or twice a week.” Astronomers expect the spacecraft will find thousands of planets orbiting other stars, and perhaps several dozen of those with environments suitable for life. Kepler revolutionized our understanding of exoplanet systems; TESS should reveal the details of those worlds that lie closer to us and therefore can be studied more exhaustively with readily available ground-based telescopes.