Within just 50 light-years from Earth, there are about 1,560 stars, likely orbited by several thousand planets. About a thousand of these extrasolar planets, known as exoplanets, may be rocky and have a composition similar to Earth’s. Some may even harbor life. Over 99 percent of these alien worlds remain undiscovered—but this is about to change.
With NASA’s new exoplanet-hunter space telescope TESS, the all-sky search is on for possibly habitable planets close to our solar system. TESS—orbiting Earth every 13.7 days —and ground-based telescopes are poised to find hundreds of planets over the next few years. This could transform astronomers’ understanding of alien worlds around us and provide targets to scan with next-generation telescopes for signatures of life. In just over a year, TESS has identified more than 1,200 planetary candidates, 29 of which astronomers have already confirmed as planets. Given TESS’s unique ability to simultaneously search tens of thousands of stars for planets, the mission is expected to yield over 10,000 new worlds.
These are exciting times for astronomers and, especially, for those of us exploring exoplanets. We are members of the planet-hunting Project EDEN, which also supports TESS’s work. We use telescopes on the ground and in space to find exoplanets to understand their properties and potential for harboring life.
Worlds around us await discovery. Take, for example, Proxima Centauri, an unassuming, faint red star, invisible without a telescope. It is one of over a hundred billion or so such stars within our galaxy, unremarkable except for its status as our next-door neighbor. Orbiting Proxima is a fascinating but mysterious world, called Proxima b, discovered only in 2016.
Scientists know surprisingly little about Proxima b. Astronomers name the first planet discovered in a system “b”. This planet has never been seen with human eyes or by a telescope. But we know it exists due to its gravitational pull on its host star, which makes the star wobble ever so slightly. This slight wobble was found in measurements collected by a large, international group of astronomers from data taken with multiple ground-based telescopes. Proxima b very likely has a rocky composition similar to Earth’s, but higher mass. It receives about the same amount of heat as Earth receives from the sun.
And that is what makes this planet so exciting: It lies in the “habitable” zone and just might have properties similar to Earth’s, like a surface, liquid water, and—who knows?— maybe even an atmosphere bearing the telltale chemical signs of life.
NASA’s TESS mission launched in April 2018 to hunt for other broadly Earth-sized planets, but with a different method. TESS is looking for rare dimming events that happen when planets pass in front of their host stars, blocking some starlight. These transit events indicate not only the presence of the planets, but also their sizes and orbits.