Venus

Venus is the second planet from the Sun and Earth’s near-twin in size, mass and bulk composition — but a radically different world in every other respect. A CO₂ atmosphere 92 times denser than Earth’s traps enormous amounts of solar heat, driving a runaway greenhouse that keeps the surface at 737 K (464 °C) — hot enough to melt lead, and hotter than Mercury despite Venus being nearly twice as far from the Sun.

Its global cloud deck — droplets of sulfuric acid 45-70 km above the surface — rotates around the planet once every four Earth days, far faster than the solid planet itself, a phenomenon called super-rotation. The planet rotates retrograde once every 243 Earth days, which is longer than its 225-day year.

Soviet Venera landers (1970-1982) briefly survived the surface and sent back the only color images of Venus’s rocky, basalt-strewn landscape. NASA’s Magellan orbiter mapped 98% of the surface with radar (1990-94), revealing extensive volcanic features. Upcoming missions include NASA DAVINCI and VERITAS, plus ESA’s EnVision — all targeting launches in the late 2020s and early 2030s.