Illustration of NASA’s Transiting Exoplanet Survey Satellite — TESS — observing an M dwarf star with orbiting planets. NASA’S GODDARD SPACE FLIGHT CENTER
Human-centric language is hard to avoid when we talk about the cosmos. Astronomers have identified thousands of suns across the universe, yet most of us think of the closest one as “the” sun. There are over 150 known moons in the solar system, but ours is called “the” moon.
Likewise, our solar system has plenty of company. We’ve observed more than 2,500 stars that have planets orbiting around them. Any planet that resides in a foreign solar system is known as an exoplanet. These distant worlds are the main focus of a NASA mission that just got underway. On April 18, 2018, the Transiting Exoplanet Survey Satellite — or “TESS” for short — launched out of Florida’s Cape Canaveral Space Station on a SpaceX Falcon 9 rocket. Its purpose? To find faraway planets. Thousands and thousands of them.
Costing less than $200 million (not including the launch expenses), TESS is a bargain-priced, high-tech telescope complete with four wide-view optical cameras. Their intended purpose is to help scientists locate hitherto-undiscovered exoplanets. “The TESS mission,” reads an April 18 press release, “will identify planets ranging from Earth-sized to gas giants, using an array of telescopes to perform a two-year survey.”
That job began in earnest on July 25, 2018, when NASA announced that the telescope’s “scientific operations” had officially started. TESS is intended to orbit Earth along a route that’s never been used by a manmade instrument before. It will complete a new circle around the home planet every 13.7 days; at its closest point in the cycle, TESS is going to be 67,000 miles (107,826 kilometers) away from us. Whenever it reaches this part of its orbit, the spacecraft will transmit a fresh batch of data down to scientists. NASA expects the first transmission to arrive in early August.
TESS is using the transit method to seek out exoplanets. The technique, which has been around since the early 2000s, is simple. Stars get slightly dimmer when planets move in front of them. So by closely monitoring the brightness levels of stars through a telescope, astronomers can tell if any exoplanets are in the neighborhood.
In March 2009, NASA launched Kepler, a space observatory built to spot exoplanets via the same transit method. To date, it’s found 2,327 confirmed planets and evidence that might hint at the existence of 2,244 others. TESS is expected to upstage Kepler. While Kepler was focused on a relatively small portion of the night’s sky, TESS is going to scrutinize 85 percent of it. Altogether, the newer spacecraft will look at more than 200,000 stars — with a higher average brightness than the ones Kepler surveyed — by the time its mission ends.