Mars, also known as the Red Planet, is the fourth planet from the Sun in the Solar System and the second-smallest planet with a diameter of 6,779 km at its equator. In Hebrew, Mars is called Ma'adim (מאדים), which means "the one who reddens" or "the red one." In Latin, Mars is known as Mārs, and in Arabic, it is called Al-Mirrikh (المريخ). Named after the Roman god of war, Mars has been a subject of human fascination for centuries due to its distinctive reddish appearance, which is caused by iron oxide (rust) on its surface. Key features of Mars include Olympus Mons, the tallest volcano and the highest peak in the Solar System, and Valles Marineris, one of the largest canyons. Mars has two small, irregularly shaped moons, Phobos and Deimos, named after the Greek words for fear and terror, respectively. The planet has been explored by numerous spacecraft, including rovers like Spirit, Opportunity, and Curiosity, which have provided valuable data about its geology, atmosphere, and potential for past or present life.