<Li> 0.146% oxygen </Li> <Li> 0.0557% carbon monoxide </Li> <P> Mars is the fourth planet from the Sun and the second - smallest planet in the Solar System after Mercury . In English, Mars carries a name of the Roman god of war, and is often referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the astronomical bodies visible to the naked eye . Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth . </P> <P> The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons . Mars is the site of Olympus Mons, the largest volcano and second - highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System . The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature . Mars has two moons, Phobos and Deimos, which are small and irregularly shaped . These may be captured asteroids, similar to 5261 Eureka, a Mars trojan . </P>

How did mars get its name and what does it mean