Animation of the orbits of the planets around the red dwarf star TRAPPIST-1f. The discovery of the planetary system 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. The closest, TRAPPIST-1b, orbits just 1.6 million kilometres from the star (just over 1% of the Earth-Sun distance), taking 1.5 days to complete an orbit. The rest of the system is very close, with TRAPPIST-1c at 2.3 million kilometres, TRAPPIST-1e, f and g within the star's habitable zone at 4.2, 5.5 and 6.7 million kilometres, and the most distant TRAPPIST-1h only at 9.4 million kilometres. The habitable zone is so close to the star as it is very cool, with a temperature of some 2500K compared to our Sun's 5800K.