Mercury

Mercury is the smallest planet in our solar system. It’s just a little bigger than Earth’s Moon. Mercury itself, though, doesn’t have any moons. It is the closest planet to the Sun, but it’s actually not the hottest. Venus is hotter.

Along with Venus, Earth, and Mars, Mercury is one of the rocky planets. It has a solid surface that is covered with craters. Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted off the surface by the solar wind and striking meteoroids. Mercury's exosphere is composed mostly of oxygen, sodium, hydrogen, helium, and potassium. Mercury doesn’t have any moons.