The newest planet-hunting spacecraft is off to a promising start

NASA’s Transiting Exoplanet Survey Satellite (TESS) has been scouring the skies for nearby worlds since it began science operations in July. Its first batch of data is now available to astronomers, and already dozens of new exoplanet candidates are awaiting follow-up data to confirm their existence.

During its initial observing campaign, the mission studied 15,900 nearby stars. In 73 cases, TESS witnessed a brief dimming of light suggesting an object, such as a planet, passed in front of the star. But not all dips in starlight are caused by planets; other processes, such as starspots or variability, also can change brightness. And some dips may be caused by companion stars, rather than orbiting planets. TESS principal investigator George Ricker of MIT told Astronomy that up to 20 percent of the new candidates will probably be ruled out of planetary status. The remaining candidates, though, are bound to be hot research commodities; some are planets astronomers have already cataloged, but Ricker estimates that six are likely newly found real planets.

Four eyes on the sky TESS’ workhorses are its four wide-field cameras, each with a 24°-by-24° field of view. The spacecraft breaks the sky up into 26 sectors, staring at each for 27 days. TESS’ current mission is set for a length of two years, during which it will cover 85 percent of the sky. The spacecraft sends back data every 13.7 days, when it makes its closest approach to Earth on its unique orbit. Most of the stars it will study lie between 30 and 300 light-years from Earth — closer and brighter than the stars studied by its predecessor, the Kepler space telescope, which means they’re also easier to follow up from the ground.

“We make alerts available to astronomers worldwide, and we continue to do that because there are a lot of amateurs with superb instruments they can use for the initial parts of the screening,” Ricker said, adding the process will likely take months or years due to the number of planetary candidates to double-check. “As we become more adept at seeking these things out, we are going to get 100 or 200 more [candidates] per sector. There will be a lot to work through. I expect there are going to be 3,000 or so potential objects of interest.” This first round represents only a fraction of the planets TESS hopes to uncover. While large planets are easiest to spot, mission planners also expect TESS to find at least 50 planets no larger than four times the mass of Earth. With TESS already off to an impressive start, this goal doesn’t seem too far out of reach.