Mars is the fourth planet from the Sun and the second smallest planet in our solar system, after Mercury. It is often described as the "Red Planet" due to the reddish appearance of its surface. The color is caused by iron oxide, or rust, which is abundant on Mars.

The size of Mars is about half that of Earth, with a diameter of approximately 6,780 kilometers (4,215 miles). Its mass is about one-tenth that of Earth, and its surface area is about one-fourth that of Earth. Mars has two moons, Phobos and Deimos, which are much smaller than Earth's moon. Phobos has a diameter of about 22.2 kilometers (13.8 miles), while Deimos has a diameter of about 12.4 kilometers (7.7 miles).