Our sister planet Venus is about the same size, density, and composition as Earth, and when its thick atmosphere was first discovered, alien-hunters wondered if it harbored lush jungles and exotic life. In fact, Venus is a hellishly hot world governed by clouds of sulfuric acid.

Venus is 26 million miles closer to the sun than Earth, but that's not the only reason it's so blazingly hot. The planet has been baked by runaway global warming. In the greenhouse effect, solar radiation reaches the planet's surface, and the planet releases some of that energy by emitting infrared radiation. But on Venus, the thick clouds and a dense atmosphere that's composed primarily of carbon dioxide trap the heat and prevent it from escaping into space. Venus's surface temperature is 860 degrees Fahrenheit, making it the hottest planetary surface in our solar system.