TOI-700 d was the first Earth-sized planet in a habitable zone announced from NASA’s TESS mission in 2020.
Astronomers led by Emily Gilbert identified it through TESS transit observations and announced the discovery on January 3, 2020. The planet circles the cool red dwarf TOI-700, about 101 light-years away in the constellation Dorado.
TOI-700 d is roughly 1.19 times Earth’s radius and completes an orbit every 37.4 days. Although it travels much closer to its star than Earth does to the Sun, its dim red-dwarf host means it receives about 88% of Earth’s incoming sunlight. That places it within the star’s habitable zone, where surface liquid water could be possible under suitable atmospheric conditions.
A common mix-up is confusing “habitable zone” with proof of habitability. TESS detected the planet and established its size and orbit, but it has not shown that TOI-700 d has oceans, an atmosphere, or life. The system contains four confirmed planets, with d as its outermost known world.