Figure 6-2 Earth’s Vital Statistics The planet symbol for Earth is ⊕. Other planets have different symbols; these are all used as shorthand for information about each world. For example, the mass of Earth is denoted M⊕. This figure provides information about Earth’s physical and orbital properties. Recall that pounds (lb) here are a unit of mass. Astronauts spend many hours watching our world as they orbit it. The image here gives you an idea of why they find it so fascinating.