Mars, the fourth planet from the Sun, is often referred to as the "Red Planet" due to its reddish appearance caused by iron oxide prevalent on its surface. It is a terrestrial planet with a thin atmosphere, approximately 1/100th the density of Earth's, and has a surface gravity about 38% of Earth's. Mars has two small moons, Phobos and Deimos, which are irregularly shaped.
The planet's surface features include polar ice caps, canyons, and volcanoes, with Olympus Mons being the largest volcano and highest known mountain in the solar system. Evidence suggests that Mars once had a much thicker atmosphere and was warmer, with liquid water existing on its surface, leading to ongoing scientific interest in the possibility of past or present microbial life.