NASA just found a planet almost the size of Earth and it's in the habitable zone of a star

Scientists with NASA announced they have discovered an Earth-sized planet that is likely rocky – and could be habitable. 

The planet, named TOI 700 e, is slightly smaller than Earth and orbits a red dwarf star called TOI 700 about 100 light-years away. It's one of four planets to orbit the star, alongside TOI 700 b, c and d. 

TOI 700 d was already known to be in the habitable zone, a discovery made possible by NASA's Transiting Exoplanet Survey Satellite (TESS), which monitors large portions of the sky for 27 days at a time to track changes in stellar brightness caused by planets.

But it took more than a year for scientists to discover TOI 700 e and learn that it was within the star's habitable zone. Its discovery was presented at the American Astronomical Society in Seattle, and a paper about the planet was accepted by The Astrophysical Journal Letters.

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What is the habitable zone?

Also known as the "Goldilocks zone," the habitable zone is the distance from a star where liquid water could exist on an orbiting planet, according to NASA. It gets its nickname because the conditions on the planet are not too cold or too hot to sustain life. 

Scientists say TOI 700 e, along with planet d, are in the "optimistic" habitable zone, which means the planet, at some point, could have had liquid water in its history. 

"This is one of only a few systems with multiple, small, habitable-zone planets that we know of," Emily Gilbert, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory who led the work, said in a statement.

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What is planet TOI 700 e like?

TOI 700 e is about 95% the size of Earth and is probably a rocky planet similar to ours.

It is about 10% smaller than planet d. Although it is the fourth planet to be discovered in the TOI 700 system, it is between planets c and d.

"If the star was a little closer or the planet a little bigger, we might have been able to spot TOI 700 e in the first year of TESS data,” said Ben Hord, graduate researcher at NASA’s Goddard Space Flight Center.

It takes TOI 700 e about 28 days to orbit its star, and it may also be a tidally locked planet, meaning it spins only once per orbit and only one side always faces the star. It's similar to how only one side of the moon is always facing Earth. 

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Are there other planets in habitable zones?

Scientists are constantly discovering planets in habitable zones that could sustain human life. 

In September, scientists also using TESS found a "super-Earth" planet about 100 light-years away from us that could host life. In 2019, water vapor was detected in the atmosphere of the planet known as K2-18b, along with temperatures that could support life. 

Scientists plan follow-up studies on the TOI 700 system as TESS searches for other systems in the universe. 

"We’re looking forward to the other exciting discoveries hidden in the mission’s treasure trove of data," said Allison Youngblood, a research astrophysicist and TESS deputy project scientist.

Follow Jordan Mendoza on Twitter: @jordan_mendoza5.