So what makes Venus hotter than Mercury? Venus has an extremely dense atmosphere composed of carbon dioxide, nitrogen, and traces of other gases, most notably sulfur dioxide. Its atmosphere is about 90 times denser than that of Earth. As the heat has no where to go, it creates an oven-like condition on the surface of Venus. Mercury doesn’t have any atmosphere. Any heat that Mercury receives from the sun is quickly lost back into space.
The average surface temperature on Venus is 464 degrees Celsius (867°F). Its atmosphere has thick, pale, yellow clouds of carbon dioxide and sulfuric acid. Carbon dioxide traps heat and prevents it from escaping to space.
Depending on location, Mercury’s airless surface can be extremely hot or extremely cold. The highest temperatures on Mercury are about 427°C (800°F). This is near the equator on the sunward side. Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -280°F (-170 degrees Celsius).