GJ 357 exoplanet system. Illustration of the exoplanets orbiting GJ 357, an M-type dwarf star that is around one-third the Sun's mass and size and about 40% cooler. The system is located 31 light-years away in the constellation Hydra and was detected by NASA's Transiting Exoplanet Survey Satellite (TESS) satellite. The blue ring denotes the habitable zone, thought to be a distance from the star where conditions may be suitable for liquid water to exist. The orbits of three exoplanets, GJ 357 b (inner orbit), GJ 357 c (middle orbit) and GJ 357 d (outer orbit) are shown relative to the habitable zone. GJ 357 d is about 6 times the mass of Earth and is located on the outer edge of its star's habitable zone. Here it receives about the same amount of stellar energy from its star as Mars does from the Sun, with a temperature of -53 C.