University of Edinburgh

BSL Astronomy Glossary - mercury - definition

Definition: One of the inner, rocky planets in our solar system, Mercury is the closest planet to the sun. It has no atmosphere to protect it from the heat of the sun on one side and the icy cold of space on the other side. This means that, during its orbit, the side of the planet facing the sun is extremely hot but the side facing away from the sun is always very cold.