A planitia designates a low-lying plain on the terrestrial planetsMercury, Venus, Moon, and Mars, on the Saturnian satellites Enceladus and Titan, and on Triton (Neptune). A planitia can extend from a few ten thousands to several millions of square kilometers across a planetary surface. Guinevere Planitia on Venus is the largest one known with a diameter of 7,520 km. Tectonism or impacts are the primary processes that can create vast low-lying plains. On planets or satellites with an atmosphere (Venus, Mars, Titan), planitiae can be subsequently modified by material deposited in the plain by wind or fluid flow.