In our solar system the Mars is the fourth planet from the sun, which is named after the Roman god of war Mars because of its obvious red color in the night sky). Phobos and Deimos are the two moons of Mars which are small and oddly-shaped, perhaps being captured asteroids. The prefix areo- refers to Mars in the same way geo- refers to Earth. The astronomical symbol for Mars is a circle with an arrow pointing northeast (Unicode: ?). This symbol is a stylized representation of the shield and spear of the god Mars, and in biology it is used as a sign for the male sex.