Which planet is closest to the sun?

Mercury is the closest planet to the sun. The temperature on the side of the planet facing the sun is as high as 430 degrees celcius. The shaded side of Mercury which faces away from the sun is bitterly cold at -180 degrees celcius. Mercury has almost no atmosphere because it has been burned off by the sun. The planet consists of bare rock, pitted and scarred by the impact of meteorites. It has extremely steep cliffs that are hundreds of kilometres long. These were formes when the planet cooled from its original molten (liquid) state, millions of years ago.