Mars is the fourth planet from the Sun, between Earth and Jupiter. The asteroid belt lies between Mars and Jupiter. The average distance of Mars from the Sun is 141 million miles (227 million kilometers). That's 1.5 times the distance from the Earth to the Sun. This means that Mars receives only about 44% the amount of sunlight we get on Earth. A Martian day is 24.6 hours long, or only about 40 minutes longer than an Earth day. An Earth year is 365.25 days long. One Martian year is 687 Earth days long, or the length of almost 2 Earth years. Mars has almost no magnetic field today, although data from the Mars Global Surveyor spacecraft shows that Mars once had a magnetic field as strong as Earth's. Mars' tiny magnetic field today provides very little protection from radiation from space. Mars has two moons, Phobos and Deimos. Phobos means "fear" and Deimos means "panic," and in Greek mythology, Phobos and Deimos were Mars' sons. Phobos orbits Mars backwards. As seen from the Martian surface, Phobos rises in the west and sets in the east about twice a day; Deimos is the further of the two moons from the planet's surface and is the smallest known moon in the entire Solar System. Phobos and Deimos are probably asteroids captured by Mars' gravity long ago. Water freezes at +32 degrees F (0 degrees C). Carbon dioxide freezes at -110 degrees F (-79 degrees C). Daytime temperatures at Mars' equator can reach +65 degrees F (+18 degrees C). Nighttime temperatures at the poles, the coldest portions of Mars, can fall to a frigid -195 degrees F (-126 degrees C). Mars is the Roman god of war. Ares is the Greek name for the Red Planet. The two main components of Earth's atmosphere are nitrogen (78%) and oxygen (20%). The two main components of Mars' atmosphere are carbon dioxide (95%) and nitrogen (3%). There is almost no oxygen in the Martian atmosphere. Mars has no liquid water on its surface. Water may be locked underground as permafrost. Water ice exists at the ice caps, though it is not known exactly how much water ice there is. The southern ice cap seems to be made of mostly carbon dioxide ice (dry ice). (caption) Mars south polar ice cap Mars has the largest volcano and the longest canyon in the Solar System. Olympus Mons, or Mount Olympus, is about 15 miles high (27 kilometers) and 372 miles wide (600 kilometers). This is about the three times higher than Mount Everest and the width of the state of Nebraska. The canyon system, Valles Marineris or Mariner Valley, would stretch from New York to Los Angeles, if located on Earth. This is a length of over 3100 miles (5000 kilometers). The Grand Canyon would fit nicely into one of the tiny side canyons. Valles Marineris is about 5 miles, or 8 kilometers, deep. The huge volcanoes in Mars' northern hemisphere are so large that they have deformed Mars' sphericity. Mars "bulges out" in its northern hemisphere. Periodically, vast dust storms cover large portions of Mars, sometimes engulfing the entire planet and obscuring its surface from view. The gravity of Mars is about one-third that of Earth. Humans walking on Mars surface would have to "bunny-hop" to get around easily, similarly to how astronauts walked on the Moon. The surface of the southern hemisphere of Mars (to the south of the Valles Marineris) is ancient and heavily cratered. The surface of the northern hemisphere, where the large volcanoes are located, is younger and shows evidence of more recent geological activity.