TRAPPIST-1, is an ultra-cool dwarf star, slightly larger than the planet Jupiter, located 39.5 light years from the Sun in the constellation Aquarius. The dwarf star has been shown to host seven temperate terrestrial planets, a larger number than detected in any other planetary system.
Astronomers first discovered three Earth-sized planets orbiting the dwarf star in 2015. A team led by Michaël Gillon at the University of Liège in Belgium detected the planets using transit photometry with the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at the La Silla Observatory in Chile. On 22 February 2017, astronomers announced four additional exoplanets around TRAPPIST-1. This work used the NASA Spitzer Space Telescope and the Very Large Telescope at Paranal, among others, and brought the total number of planets to seven, of which three are considered to be within its habitable zone; conceivably, the others also could be habitable as they may possess liquid water somewhere on their surface.