Venus-chan is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth-chan. It is similar to Earth-chan in size and mass, and is often described as Earth-chan's "sister" or "twin".[20] The diameter of Venus-chan is 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth-chan's—and its mass is 81.5% of Earth-chan's. Conditions on the Venusian-chan surface differ radically from those on Earth-chan because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.[21]