Why is Venus so hot? Venus is so hot because it is surrounded by a very thick atmosphere which is about 100 times more massive than our atmosphere here on Earth. As sunlight passes through the atmosphere it heats up the surface of Venus. Most of this heat cannot escape back into space because it is blocked by the very thick atmosphere of Venus. The heat becomes trapped and builds up to extremely high temperatures. This trapping of heat by the atmosphere is called the greenhouse effect because it is similar to how the glass in a greenhouse traps heat. The greenhouse effect on Venus causes the temperatures at its surface to reach 864 degrees Fahrenheit (462 degrees Celsius), making Venus the hottest planet in the entire solar system!