NASA's planet-hunting mission TESS has found its first potentially habitable exoplanet the size of Earth orbiting a star about 100 light-years from Earth, according to the agency.

The findings were announced during the 235th meeting of the American Astronomical Society on Monday in Honolulu.

The planet is part of a multi-planet system around TOI 700, a small, cool M-dwarf star in the Dorado constellation. It's only about 40% of our sun's mass and size, with half of the surface temperature.

The planet is known as TOI 700 d, one of three orbiting the star. It's at just the right distance to support liquid water on the surface in the star's habitable zone.

Astronomers confirmed their discovery using NASA's Spitzer Space Telescope infrared capabilities with follow-up observations. They also modeled the planet's potential environment to further investigate its habitability.

The find is exciting to astronomers because it's one of a select few potentially habitable planets discovered outside of our solar system that happens to be the size of Earth.

TOI 700 d is the outermost of the three planets, completing a single orbit around the star every 37 Earth days. From its smaller star, the planet receives about 86% of the energy that our sun supplies the Earth. The planet is thought to be tidally locked, meaning one side is always in daylight.

The other two planets in the system, TOI 700 b and c, are different. The innermost planet, b, is the size of Earth and rocky like our planet and zips around the star every 10 Earth days. The second planet, c, is considered to be gaseous and between the size of Earth and Neptune, completing an orbit every 16 Earth days.

Initially, the star was miscategorized as much hotter, leading astronomers to think that the planets orbiting it would be too close and hot to support life.

CNN