TRAPPIST-1g exoplanet. Animation showing one full rotation of the TRAPPIST-1g exoplanet. This exoplanet is one of seven Earth-sized terrestrial (rocky) planets discovered orbiting the ultra-cool Jupiter-sized dwarf star TRAPPIST-1. The planets are named b-h from closest to furthest from the star. TRAPPIST-1g has a diameter of around 14, 398 kilometres and a mass some 0.57 times that of the Earth. It orbits at a distance of about 6.75 million kilometres, with an orbital period of around 12.35 days. TRAPPIST-1g is shown here as a Neptune-like world with an atmosphere, clouds, water and ice. The TRAPPIST-1 planets are tidally locked, permanently facing the star, leading to large temperature difference between the two sides of each planet. The two closest planets are the warmest, and the two outer planets are the coldest. Three planets (e, f, g) orbit in the habitable zone, with varying amounts of liquid water present. TRAPPIST-1 is 40 light years from Earth, in the constellation of Aquarius. The planets were discovered and studied in 2015 and 2017, using the ground-based TRAPPIST (Transiting Planets and Planetesimals Small Telescope) and NASA's Spitzer Space Telescope (SST).