Venus is nearly identical to Earth in size and mass, which is why scientists once hoped it might harbor life. Then we learned the truth. Its atmosphere is 96% carbon dioxide, creating a runaway greenhouse effect that traps heat so effectively the surface reaches 465°C — hotter than Mercury despite being farther from the Sun.

The atmospheric pressure on Venus is 90 times Earth's — equivalent to being 900 meters underwater. Thick clouds of sulfuric acid blanket the planet, and the surface pressure has crushed every lander sent there within hours.