Venus is the hottest planet in our solar system. Although it is similar in structure and size to Earth, Venus has a thick atmosphere that traps heat in a runaway greenhouse effect, making it the hottest planet. The mean temperature of Venus is 864 degrees Fahrenheit (462 degrees Celsius). Despite being farther from the Sun than Mercury, Venus is hotter than Mercury because its carbon dioxide and sulfuric acid-filled atmosphere causes a greenhouse effect, which traps heat. Mercury, on the other hand, does not have an atmosphere, so there is nothing to trap the heat at the planet.