Seven Earth-sized planets orbit the ultracool dwarf star TRAPPIST-1, 40 light-years away from the Earth . This makes TRAPPIST-1 the planetary system with the largest number of Earth-sized planets discovered so far. These planets are also relatively temperate, making them a tantalizing place to search for signs of life beyond our Solar System. Now, an international team of astronomers has presented a study in which they used the NASA/ESA Hubble Space Telescope to screen four planets in the system — TRAPPIST-1d, e, f and g — to study their atmospheres .
Three of the planets orbit within the system’s habitable zone, the region at a distance from the star where liquid water — the key to life as we know it — could exist on the surface of a planet. The fourth planet orbits in a borderline region at the inner edge of the habitable zone. The data obtained rule out a cloud-free hydrogen-rich atmosphere for three of the planets — but for the fourth planet, TRAPPIST-1g, such an atmosphere could not be excluded .
Read the full article at Space Telescope.