Illustration of the exoplanet LP 791-18 d. This Earth-size planet orbits a red dwarf star in the constellation Crater, around 90 light years from Earth. There are two other known planets in this system, LP 791-18 b and LP 791-18 c (blue dot at right), which is seven times more massive than Earth. Interactions with LP 791-18 c are causing the orbit of LP 791-18 d to become increasingly elliptical. When LP 791-18 d passes closest to its star, gravitational forces deform the planet, creating internal friction and heat that is released through volcanoes. The outgassing of the volcanoes could lead to the formation of an atmosphere, which along with its position at the edge of its stars habitable zone, could lead to liquid water on the planets surface.