Which planet is the hottest?

Venus is the hottest planet in the solar system, with an average surface temperature of about 465 degrees Celsius, hot enough to melt lead. Surprisingly, it is not the closest planet to the Sun; that is Mercury. The reason Venus is hotter is its thick atmosphere, composed mainly of carbon dioxide with clouds of sulphuric acid, which traps heat in a runaway greenhouse effect. Sunlight passes through, warms the surface, and the heat cannot escape, driving temperatures to extremes and keeping them nearly constant across the entire planet, day and night. Mercury, by contrast, has almost no atmosphere, so although its daytime side gets extremely hot, its nighttime side becomes bitterly cold. Venus dense atmosphere also creates crushing surface pressure, about 90 times that of Earth. It serves as a stark warning of the greenhouse effect power.