Which is the smallest planet?

Mercury is the smallest of the eight planets, with a diameter of about 4,880 kilometres — barely larger than our Moon. It is also the closest planet to the Sun, whipping around it in just 88 Earth days. Despite its nearness to the Sun, it is not the hottest planet, because it has almost no atmosphere to trap heat, leading to extreme swings between scorching days and freezing nights. Since Pluto was reclassified as a dwarf planet in 2006, Mercury has held the title of smallest planet.