NASA's TESS satellite discovers the second Earth-sized world in the planetary system

NASA’s TESS satellite discovers the second Earth-sized world in the planetary system

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Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), scientists have identified an Earth-sized world called TOI 700 E that orbits within its star’s habitable zone, the range of distances where the liquid water could occur on the surface of a planet. The world is 95% the size of Earth and probably rocky.

TESS is a space telescope that is part of NASA’s Explorers Program and is designed to search for exoplanets using the transit method over an area 400 times larger than that covered by the Kepler mission.

Astronomers previously discovered three planets in this system, called TOI 700 B, C and D. Planet d also orbits in the habitable zone. But it took the scientists an extra year of TESS observations to discover TOI 700 E.

“This is one of the few systems with multiple small planets in habitable zones that we know of,” said Emily Gilbert, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Southern California, who led the work. “That makes the TOI 700 system an exciting prospect for further monitoring. Planet E is about 10% smaller than planet D, so the system also shows how additional TESS observations help us find ever smaller worlds.”

Gilbert presented the result on behalf of his team at the 241st meeting of the American Astronomical Society in Seattle. The Astrophysical Journal Letters accepted a paper on the newly discovered planet. TOI 700 is a small, cool M dwarf star located about 100 light-years from away in the southern constellation of Dorado. In 2020, Gilbert and others announced the discovery of the Earth-sized habitable zone planet D, which is in a 37-day orbit, along with two other worlds.

The innermost planet, TOI 700 B, is about 90% the size of Earth and orbits the star every 10 days. TOI 700 C is 2.5 times larger than Earth and completes one orbit every 16 days. The planets are likely tidally locked, meaning they rotate only once per orbit, so that one side always faces the star, just as one side of the Moon always rotates toward Earth.

TESS monitors large swaths of the sky, called sectors, for about 27 days at a time. These long gazes allow the satellite to track changes in stellar brightness caused by a planet crossing in front of its star from its perspective, an event called a transit. The mission used this strategy to observe the southern sky beginning in 2018, before turning to the northern sky. In 2020, it returned to the southern sky for additional observations. The additional year of data allowed the team to refine the original sizes of the planets, which are about 10% smaller than initial estimates.

«If the star were a little closer or the planet a little bigger, we could have detected TOI 700 E in the first year of TESS data.said Ben Hord, a doctoral candidate at the University of Maryland, College Park and a graduate researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But the signal was so weak that we needed an additional year of transit observations to identify it.”

TOI 700 E, which may also be tidally locked, takes 28 days to orbit its star, placing the planet between planets C and D in the so-called optimistic habitable zone. Scientists define the optimistic habitable zone as the range of distances from a star where liquid surface water could be present at some point in a planet’s history. This area straddles the conservative habitable zone, the range where researchers assume liquid water could exist for most of the planet’s lifetime. TOI 700 D orbits in this region.

Finding other systems with Earth-sized worlds in this region helps planetary scientists learn more about the history of our own solar system. Follow-up study of the TOI 700 system with space and ground observatories is ongoingGilbert said, and may shed more light on this rare system.

“TESS has just completed its second year of northern sky observations,” said Allison Youngblood, a research astrophysicist and associate TESS project scientist at Goddard. “We look forward to the other exciting discoveries hidden in the mission’s treasure trove of data.”

TESS is a NASA Astrophysics Explorer mission led and operated by the Massachusetts Institute of Technology in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center. Additional partners include Falls Church, Va.-based Northrop Grumman; the NASA Ames Research Center in Silicon Valley in California; the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts; the MIT Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories around the world are participating in the mission.

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