NASA announces discovery of potentially habitable Earth-sized planet

In an announcement made today, NASA says its Transiting Exoplanet Survey Satellite (TESS) first spotted planet TOI 700 d, which was then confirmed using the Spitzer Space Telescope.

NASA scientists say conditions on the planet "may allow the presence of liquid water on the surface."

"TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars," said Paul Hertz, astrophysics division director at NASA Headquarters in Washington.

"Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS.

"Confirming the planet's size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."

According to NASA, TOI 700 is a small, cool M dwarf star located just over 100 light-years away in the southern constellation Dorado.

It's roughly 40 per cent of the Sun's mass and size and about half its surface temperature.

NASA says TOI 700 d is one of only a few Earth-size planets discovered in a star's habitable zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA's Kepler Space Telescope.