NASA wants to find aliens—it’s no longer shy of making that an explicit goal. There are plenty of places to look. With more than 3,700 exoplanet discoveries and counting, we know planets are everywhere, and every star system probably possesses at least one planet. Moreover, we know of about 53 exoplanets that possess the best chances of being habitable to life—all potential targets for finding extraterrestrials of some kind and giving us future destinations to travel to if we ever master interstellar spaceflight. These discoveries have surged in the past decade, and they’re likely to get even more plentiful.
Monday evening, aboard a SpaceX Falcon 9 rocket, NASA will launch into orbit the Transiting Exoplanet Survey Satellite, or TESS, a new exoplanet hunter aimed specifically at uncovering more exoplanets closer to Earth. “TESS is really about trying to find planets around the nearest and brightest stars,” says Tom Barclay, a TESS mission scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland. “We want to find planets that are going to be the touchstone planets to study for years to come.”
Up until now, the flagship exoplanet finder has been Kepler, a scrappy space telescope launched in 2009 to determine whether planets in other star systems were common. It was extremely successful at answering that question and greatly raised in our minds the odds that life elsewhere existed. But now, scientists want to know what the best targets to study in greater detail are, and we want them to be as close to Earth as possible.
Kepler has punched well above its weight in terms of planetary science, but it had its limitations. The telescope could only peer into a few regions of space at a time, so it was limited to looking at about 100,000 stars, located between 300 and 1,000 light-years away.
TESS is designed to be much pickier. It’s peering off into star systems about 30 to 100 light-years away, but it will have a field of view that’s 400 times bigger than Kepler’s. In a single snapshot, its four cameras can look at an incredibly big fraction of the sky, rotating every month, and covering roughly half the sky every six months. According to Barclay, this should cover observations for at least 200,000 stars, and potentially millions.
TESS will use the same technique as Kepler for finding exoplanets. The key is to look for transiting planets — as an object orbiting a star moves in front of the star, its passage causes a slight dimming in the star’s brightness from our perspective, indicating there’s an object in the vicinity, and studying the frequency and extent of that dimming lets astronomers figure out whether there’s an exoplanet at play.
Where TESS really shines (not apologizing for this pun) is its ability to find exoplanets orbiting cooler stars. For a long time, it was assumed only sunlike stars were capable of sustaining Earth-like planets. We now know that red dwarf stars (such as Proxima Centauri, home to the closest known exoplanet) actually have a stunning ability to possess rocky planets within their habitable zones, which greatly increases the odds life might be able to survive on those worlds. And red dwarfs make up more than 70 percent of stars in the universe. TESS, more than any other exoplanet hunter, has an augmented ability to detect objects around cooler stars like red dwarfs—a notable challenge given how much more dim these stars tend to be.
It’s important to note, TESS is not designed to do the heavy lifting here to help us find Earth 2.0. TESS can provide radius and size of a new planet, its orbit, and other information from which density can be extrapolated. From there, we can determine if a planet is rocky, and that will highlight whether it’s a good target for potential habitability.
After figuring out what targets are worth studying, TESS’s job is over—it doesn’t really have the tools to learn more about those planets. It will take more powerful instruments, like the Mauna Kea Observatories in Hawaii, or the upcoming James Webb Space Telescope (the spiritual successor to the Hubble Space Telescope) to focus closer on these worlds and determine what kinds of atmospheres they might have, whether there are biosignatures indicating potential signs of life, and other factors that will actually tell us whether an exoplanet is habitable, and possibly home to current aliens.
“It’s really in some ways, James Webb’s ‘finder’ scope,” says Barclay. “The James Webb telescope is really a key to this story.”
James Webb, unfortunately, won’t launch until 2020—and that’s assuming there aren’t any more delays. But once it’s up there, it’s going to have plenty to do, likely thanks to TESS.
The mission’s time frame coincides pretty smoothly with the end of Kepler. After Monday’s launch from Cape Canaveral, Florida, the spacecraft will start making observations in early June, which is roughly the same time Kepler will run out of fuel and eventually find itself pushed out of its orbit by solar winds. TESS, on the other hand, will be placed in an elliptical orbit that no object has ever flown in before, which could allow it to stay in space for decades, maybe even more than a century. Its primary mission is only two years, but NASA is already thinking about how to extend its mandate should everything run smoothly. Barclay’s main job is actually to figure out how to leverage TESS to study more than just exoplanets, like asteroids near Jupiter, distant galaxies, supermassive black holes, and studying stars themselves.
Only a tiny fraction of the hundreds of thousands of stars TESS will study will lead to exoplanets worth investigating in follow-up research, but that still leaves, at minimum, several dozen targets. And even if only one of them exhibits signs of extraterrestrial life, that will still make for the greatest discovery in all of history.