Image obtained from http://rocksfromspace.open.ac.uk/Mercury.htm
Mercury is the innermost and smallest planet in our solar system. It orbits the Sun every 88 days. Since it is so close to the Sun it can only be seen during the morning or evening twilight. Mercury is similar to Earth’s moon as it is heavily cratered.
Mercury’s atmosphere, when it is able to maintain one, consists of hydrogen, helium, sodium, oxygen, potassium, and calcium. Mercury is too small for its gravity causing its atmosphere to be unstable.