NASA Scientists Discover Earth-Sized Planet in Habitable Zone

Scientists from NASA have made a groundbreaking discovery using the Transiting Exoplanet Survey Satellite (TESS) – an Earth-sized planet in the habitable zone, where liquid water could potentially exist on its surface. The planet, called TOI 700 e, is 95% Earth’s size and likely rocky.

Astronomers had previously discovered three planets in this system, called TOI 700 b, c, and d. Planet d also orbits in the habitable zone, but scientists needed an additional year of TESS observations to discover TOI 700 e.

“This is one of only a few systems with multiple, small, habitable-zone planets 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 additional 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.”

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The TOI 700 system is located around 100 light-years away in the southern constellation Dorado and orbits a small, cool M dwarf star. The innermost planet, TOI 700 b, is about 90% Earth’s size and orbits the star every 10 days. TOI 700 c is over 2.5 times bigger than Earth and completes an orbit every 16 days. The planets are probably tidally locked, meaning they spin only once per orbit such that one side always faces the star, similar to one side of the Moon always facing Earth.

TESS, which monitors large swaths of the sky, was able to detect the planet by tracking changes in stellar brightness caused by a planet crossing in front of its star from our perspective, an event called a transit. The mission observed the southern sky starting in 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 planet sizes, which were about 10% smaller than initial calculations.

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TOI 700 e takes 28 days to orbit its star, placing it between planets c and d in the so-called optimistic habitable zone. This zone is defined as the range of distances from a star where liquid surface water could be present at some point in a planet’s history, and extends to either side of the conservative habitable zone, where researchers hypothesize liquid water could exist over most of the planet’s lifetime.

Follow-up study of the TOI 700 system with space- and ground-based observatories is ongoing and may yield further insights into this rare system.

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

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