Animation of the planets around the red dwarf star TRAPPIST-1f. The discovery of the planetary system was announced in February 2017. They were detected by observing the small dip in light levels as they pass in front of the star as seen from Earth. 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. |