Venus

Venus is nearly Earth's twin in size and bulk composition — and a cautionary tale of climate gone catastrophic. A runaway greenhouse effect has driven its surface temperature to 465 °C, hotter than Mercury's noon, beneath a 92-bar atmosphere of CO₂ and clouds of sulphuric acid. It rotates backwards once every 243 Earth days, slower than its 225-day orbit. The surface, hidden from optical view, was finally mapped in the 1990s by radar — revealing volcanic plains, mountain ranges, and few impact craters, hinting at recent global resurfacing.

The atmosphere is 96.5% carbon dioxide, with thick clouds of sulphuric acid droplets at 50-70 km altitude. Surface pressure is 92 times Earth's — equivalent to being nearly a kilometre underwater. Despite the slow rotation, super-rotating winds at cloud level whip around the planet in just four Earth days. Lightning has been detected, and the dayside glows a deep red at the surface.

Roughly 80% of the surface is volcanic plains, with two highland "continents" — Ishtar Terra in the north and Aphrodite Terra near the equator. There are over 1,600 major volcanoes, including Maat Mons. The crater record suggests the surface is geologically young — about 300-700 million years old — possibly resurfaced in a global volcanic event. In 2023, archival Magellan radar data revealed a volcanic vent that visibly changed shape, the first direct evidence of ongoing eruptions.

More than 40 missions have been sent. The Soviet Venera programme achieved the only successful surface landings — Venera 7 transmitted from the surface for 23 minutes in 1970; Venera 13 returned colour panoramas in 1982. NASA's Magellan radar-mapped 98% of the surface from 1990-94. After a long lull, the late 2020s bring three new missions: NASA's DAVINCI atmospheric probe and VERITAS radar mapper, plus ESA's EnVision orbiter, all launching by 2031.