Using data from NASA’s Transiting Exoplanet Survey Satellite, scientists have identified an Earth-sized world, called TOI 700 e, orbiting within its star’s habitable zone – the range of distances where liquid water could occur on the surface of a planet. The world is 95% the size of Earth and probably rocky.
Astronomers have previously discovered three planets in this system, called TOI 700 b, c and d. The planet also orbits in the habitable zone. But scientists needed an additional year of TESS observations to discover TOI 700 e.
“It’s one of the few systems with multiple habitable small planets that we know of,” said Emily Gilbert, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Southern California, who led the work. “This makes the TOI 700 system an exciting prospect for further follow-up. Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find smaller and smaller worlds. »
Gilbert presented the result on behalf of his team at the 241st meeting of the American Astronomical Association in Seattle. An article on the newly discovered planet has been accepted by The Letters from the Astrophysical Journal.
TOI 700 is a small, cool M dwarf star located about 100 light-years away in the southern constellation Dorado. In 2020, Gilbert and others announced the discovery of the Earth-sized and habitable-zone planet d, which sits 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 is more than 2.5 times larger than Earth and completes an orbit every 16 days. Planets are probably tidally locked, meaning they only rotate once per orbit, so one side always faces the star, just like one side of the Moon always faces 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 passing in front of its star from our vantage point, an event called a transit. The mission used this strategy to observe the southern sky from 2018, before turning to the northern sky. In 2020 it returned to the southern sky for additional observations. The extra year of data allowed the team to refine the original sizes of the planets, which are about 10% smaller than the initial calculations.
“If the star was a little closer or the planet a little bigger, we might have been able to spot TOI 700 th in the first year of TESS data,” said Ben Hord, a PhD student 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 can also be tidally locked, takes 28 days to orbit its star, placing planet e 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 zone extends on either side of the conservative habitable zone, the range where researchers speculate liquid water could exist for most of the planet’s life. TOI 700 orbits in this region.
The discovery of other systems with Earth-sized worlds in this region helps planetary scientists learn more about the history of our own solar system.
A follow-up study of the TOI 700 system with space and ground observatories is underway, Gilbert said, and could yield new insights into this rare system.
“TESS has just completed its second year of observations of the northern sky,” said Allison Youngblood, research astrophysicist and assistant TESS project scientist at Goddard. “We look forward to the other exciting discoveries hidden in the mission’s data trove. »
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