Venus

Venus is hidden beneath a continuous, bright cloud layer. A powerful greenhouse effect, driven by abundant carbon dioxide, raises surface temperatures to about 450 °C. Together with poisonous gases and an atmospheric pressure near 90 bar, these conditions destroy surface probes within hours. Because visible light cannot see through the clouds, the planet's surface is mapped with radar; the Magellan spacecraft produced detailed maps and elevation measurements.

Venus is close to Earth in diameter and is often considered broadly similar in internal structure, possibly including a comparable core. One major unresolved question is its extremely slow retrograde rotation: unlike most solid planets, Venus turns in the opposite direction, and the origin of that spin state is still not fully explained.