The Transiting Exoplanet Survey Satellite (TESS) launched yesterday at 6:51 p.m. Eastern Daylight Time from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida. The telescope is expected to discover thousands of distant planets, including rocky and habitable worlds, around nearby bright stars across the sky during its 2-year primary mission.
“I’m very excited that we are now following up the Kepler mission with the TESS mission,” said Paul Hertz, director of the Astrophysics Division at NASA in Washington, D. C., during a late March press conference. “It’s perfect timing that we’ll be launching TESS to continue the great activity of looking for planets around stars other than our Sun and thinking about what [those discoveries] might mean for life in the universe.”
A New Orbit
Designed and built by scientists at NASA and the Massachusetts Institute of Technology (MIT) in Cambridge, TESS took to the skies aboard a SpaceX Falcon 9 rocket. The satellite’s eventual 13.7-day orbit around Earth will be highly elliptical and rely on the Moon’s gravity for long-term stability. By orbiting in resonance with the Moon, TESS will be able to maintain its path without using any fuel to course correct once it reaches orbit.
“We’re going to be in a unique, first-time orbit that I think other missions in the future will end up using,” said Jeff Volosin, TESS project manager at Goddard Space Flight Center in Greenbelt, Md. “Once we’re in orbit, we can survive for decades without any additional propulsion.”
An All-Sky Approach
After achieving orbit, TESS will search for exoplanets using the same method that the Kepler Space Telescope does, by watching a star for small changes in brightness as a planet passes in front of it and temporarily blocks a small fraction of starlight. The pioneering Kepler mission used this transit method to detect thousands of possible worlds and measure their sizes and orbits.
TESS’s mission, however, surpasses Kepler’s in an important way. Whereas Kepler stared continuously at one small patch of the sky for 4 years, TESS will search for exoplanets across more than 85% of the sky, an area approximately 350 times larger than Kepler observed during its primary mission.
The telescope can do this by combining wide-field optics and an efficient search pattern. “The coverage of the TESS cameras is unprecedented in terms of the amount of sky that they can actually see at any given time,” said TESS principal investigator George Ricker of MIT’s Kavli Institute for Astrophysics and Space Research. Each of TESS’s four cameras can observe an angular area equal to 2,304 full Moons, or the approximate span of the constellation Orion.
With that large eye, TESS will execute a “step and stare” search pattern that will let it cover most of the sky in just 2 years. At each step, the telescope will observe a 24° × 95° patch of the sky for 27 days before moving on to a new swath of the same dimensions, systematically scanning first the southern and then the northern celestial hemisphere.
Expanding upon Kepler’s Legacy
Although TESS’s planet detection method is identical to Kepler’s, the just-launched instrument will observe stars 10 times closer and 100 times brighter than those observed by its predecessor. With more than 200,000 target stars, project scientists expect that TESS will discover more than 20,000 exoplanets, hundreds of which will likely be Earth sized.
The telescope’s “sweet spot,” according to TESS deputy director of science Sara Seager, who is an MIT planetary scientist, will be finding exoplanets that orbit small red dwarf stars around half the size of the Sun, like the star that hosts the TRAPPIST-1 planets.
Because the target stars will be relatively bright, Seager added, many of the soon-to-be-discovered exoplanets likely will be good candidates for follow-up observations by future ground- and space-based telescopes. Combined with measurements from TESS, follow-up observations could reveal the masses, compositions, and atmospheres of some of those planets.
“By doing those measurements, we hope to actually identify all the worlds we’ve been dreaming about,” Seager said. She and the team would be excited to see “hot super-Earths that may have liquid lava lakes or water worlds that may be 50% or more by mass water—like scaled up versions of Jupiter’s icy moons—or even rocky worlds of all different kinds. And even, maybe, ones that have thin atmospheres reminiscent of Earth’s.”
TESS is expected to spend the first 2 months after launch performing tests and calibrations before beginning its planet hunt in June and releasing its data to the public soon thereafter.
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer
Cartier, K. M. S. (2018), Exoplanet-hunting telescope launches, Eos, 99, https://doi.org/10.1029/2018EO096785. Published on 19 April 2018.
Text © 2018. The authors. CC BY-NC-ND 3.0
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