Mars

Mars is the fourth planet from the sun and the second-smallest planet in the solar system after Mercury, named after the Roman god of the war. It is often referred to as a red planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscence both of the impact crater of the moon, and the volcanoes, valleys, deserts, and polar ice caps of the earth. The rotational period and the seasonal cycles of Mars are likewise similar to those of earth, as it was the tilt that produces the seasons. Mars is the site of the Olympus Mons, the largest volcano and the second-largest known mountain in the solar system, and the Valles Marineris, one of the largest canyons in the solar system. Until the first successful Mars flyby in 1965 by Mariner 4, many speculated about the presence of the liquid water on the planet surface. This was based on observed periodic variation in the light and the dark patches, particularly in the polar latitude, which appeared to be seas and continents. Geological evidence gathered by the unmanned mission suggested that Mars once have a large scale of water coverage on the surface on some earlier stages of existence.