Venus is only slightly smaller than the Earth, and so has enjoyed billions of years of a warm heart. But for this planet, sometimes called Earth's sister, that heat has betrayed it. That planet is now wrapped in suffocating layers of a poisonous atmosphere made of carbon dioxide and sulfuric acid. The pressures on the surface reach almost 100 times the air pressure at Earth's sea level. The average temperatures are more than 700°F, more than hot enough to melt lead, while the deepest valleys see records of more than 900°.