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Scientists have discovered an Earth-sized world that is likely rocky and 95% of the size of Earth. The planet, called  TOI 700 e, is orbiting around a star and could have liquid water on it, NASA says. 

This is the fourth planet discovered in the TOI 700 system – the other planets are named TOI 700 b, c, and d – which is 100 light-years away. TOI 700 is a star the planets orbit around, but only d and e orbit in the “habitable zone.”

A habitable zone, also known as “Goldilocks zone,” is an area that is just the right distance from a star that water can exist on a planet’s surface and the conditions are neither too hot nor too cold for life. 

“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. 

Gilbert, who led the work, said the newly discovered planet e is 10% smaller than planet d. TOI 700 e takes 28 days to orbit its star, whereas d is on a 37-day orbit.

The team discovered the planets during Transiting Exoplanet Survey Satellite, or TESS, observations, which were designed to discover more planets and stars. 

TESS’s two-year mission allowed scientists to survey solar systems and monitor the brightness of stars for periodic drops caused by planets moving past them. That mission ended in 2020, but TESS expanded, and the new planet was discovered during an additional year of the mission. 

“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, a graduate researcher at NASA’s Goddard Space Flight Center. “But the signal was so faint that we needed the additional year of transit observations to identify it.” 

So far, the satellite has created imaging for about 75% of the sky and found 66 new exoplanets, or worlds beyond our solar system. It also indicated 2,100 candidates that astronomers are working to confirm if they are exoplanets. 

The new discovery of planet e proves the satellite can help “us find smaller and smaller worlds,” Gilbert said.