Mars, named after the Roman god of war, has been documented since ancient times. Its reddish color has intrigued mankind throughout the ages, often shining as the third brightest object in the night sky after the Moon and Venus. But, with the exception of a few geographic features detected by telescope and the discovery of two small moons, relatively little was known about the Red Planet prior to the dawn of the "Space Age." Four decades of robotic international exploration of Mars has yielded much information, hopefully in preparation for a future human expedition there. -------------------------------------------------------------------------------- PHYSICAL CHARACTERISTICS Mars has an average diameter of 4,217 miles. This is about half the size of Earth, and about twice the size of Earth's moon. Despite its small size, Mars has approximately the same land area as Earth, primarily due to an absence of liquid water on its surface. The mass of Mars is about 10 percent that of Earth, and its gravity is about 38 percent as strong as our planet. The density of martian land is 3.9 times greater than liquid water -- on Earth, land density is 5.5 times greater. Mars has no detectable magnetic field. -------------------------------------------------------------------------------- ORBIT Mars is the fourth planet in the solar system, counting outward from the sun. It is located between the Earth and Jupiter, and is about 1.5 times farther away from the sun than Earth. The martian orbit around the sun is elliptical and varies in distance from a maximum of 154.8 million miles to a minimum of 128.4 million miles. It takes Mars 687 Earth-days to complete one revolution around the sun. A martian day, or period of rotation, is comparable to 24 hours, 37 minutes, 23 seconds on Earth. The planet's poles are tilted on an axis of 25 degrees, which creates martian seasons similar to those on Earth. -------------------------------------------------------------------------------- ENVIRONMENT The martian atmosphere is composed of 95.3 percent carbon dioxide, 2.7 percent nitrogen and 1.6 percent argon. This would be sufficient to suffocate a human in a matter of minutes. The atmospheric pressure there is about 1 percent that of Earth's. Surface winds have been measured to a maximum of 80 m.p.h. -- comparable to hurricane force on Earth. Dust storms occur frequently on Mars. These can be local, regional or can cover the entire planet. Dust can reach as high as six miles above the surface and settles very slowly. Surface temperatures average -64 degrees Fahrenheit, measured from a minimum -199 degrees Fahrenheit during polar night to a maximum +80 degrees Fahrenheit at the martian equator. -------------------------------------------------------------------------------- GEOGRAPHY The highest point on Mars is the Olympus Mons, a large shield volcano about 16 miles high and 370 miles across. This surface feature covers about the same area as the state of Arizona. The martian canyon system of Valles Marineris is the largest and deepest in the solar system. It runs more than 2,500 miles and has plateaus that extend upward from the canyons to altitudes of three to six miles. Martian "canals" were documented by astronomers over 100 years ago, and were believed to have been constructed by living creatures. These are believed to be large channels cut by ancient rivers. -------------------------------------------------------------------------------- MOONS Mars has two moons, Phobos (Fear) and Deimos (Terror). Each was named for a particular attribute assigned to sons of the Greek god of war. Phobos has an average diameter of about ten miles and orbits at a distance of 5,850 miles from Mars. Deimos has an average diameter of about five miles, orbiting the Red Planet at a distance of 14,600 miles.
