Venus ♀

Venus has the densest atmosphere of any terrestrial planet, composed of roughly 96.5 percent carbon dioxide with clouds of sulfuric acid. The surface atmospheric pressure is about 92 times that of Earth, equivalent to being almost a kilometer beneath the ocean. A runaway greenhouse effect traps solar energy, heating the surface to an average of 464 degrees Celsius -- hot enough to melt lead and making Venus the hottest planet despite being farther from the Sun than Mercury.

Venus's surface is dominated by volcanic plains, with over 1,600 major volcanoes identified. Maxwell Montes, the highest mountain, rises about 11 km above the mean surface level. The planet rotates extremely slowly and in the opposite direction to most planets, so the Sun rises in the west and sets in the east. A single day on Venus (243 Earth days) is actually longer than a Venusian year (225 Earth days).

The Soviet Venera program achieved remarkable firsts at Venus, including the first atmospheric entry (Venera 4, 1967), first soft landing (Venera 7, 1970), and first surface photographs (Venera 9, 1975). NASA's Magellan mission (1990-1994) used radar to map 98 percent of the surface at high resolution. JAXA's Akatsuki orbiter continues to study the atmospheric dynamics. Future missions including NASA's VERITAS and ESA's EnVision aim to unlock remaining mysteries about Venus's geology and possible past habitability.