Animation of the view from the surface of the extrasolar planet TRAPPIST-1f, with its parent star and other planets in the sky. The planetary system around the cool red dwarf star TRAPPIST-1 was announced in February 2017. The system contains seven rocky planets, five of which are a similar size to Earth, and three of which orbit within the star's habitable zone. TRAPPIST-1f is around 4% wider than Earth but has just two-thirds of its mass. It orbits just 5.5 million kilometres from the star, less than 4% of the Earth-Sun distance, taking just nine days to complete an orbit. This tight orbit is still in the star's habitable zone as it is very cool, with a temperature of some 2500K compared to our Sun's 5800K.