Mars is a blood red planet named after the Roman god of war, and its symbol portrays his shield and spear. It has two very small lopsided moons, Deimos and Phobos, named after the two horses that pull his chariot. The planet's red color comes from iron oxide contained in the soil and rocks. Water has been found on Mars, including in frozen ice caps on the poles, in a huge slab of ice 130 feet thick and twice the size of Texas just under the soil near the Martian equator, and in photos from orbiters that NASA believes show evidence of flowing water on the surface. In 1997, the solar-powered rover Sojourner, which weighed 25 pounds, survived on Mars for 3 months and drove a total of just over 300 feet, proving that rovers could be landed on other planets and driven from Earth. In 2004, the larger Spirit and Opportunity rovers traveled much farther and communicated with Earth for over 10 years. In 2012, the car-sized, plutonium-powered Curiosity rover, equipped with rock-vaporizing lasers, began looking for life in the form of tiny microbes. Landing rovers safely on Mars has been difficult: early missions used giant protective airbags, while Curiosity was slowed by a parachute and retrorockets before being lowered gently to the surface by a tether system called the sky crane.