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Mars at a Glance (from the JPL Press Kit)
General
One of five planets known to ancients; Mars was Roman god of war, agriculture and the state
Reddish color; occasionally the 3rd brightest object in night sky after the Moon and Venus
Physical Characteristics
Average diameter 4,217 miles (6,780 kilometers); about half the size of Earth, but twice the size of Earth's Moon
Same land area as Earth
Mass 1/10th of Earth's; gravity only 38 percent as strong as Earth's
Density 3.9 times greater than water (compared to Earthís 5.5 times greater than water)
No planet-wide magnetic field detected; only localized ancient remnant fields in various regions
Orbit
Fourth planet from the Sun, the next beyond Earth
About 1.5 times farther from the Sun than Earth is
Orbit elliptical; distance from Sun varies from a minimum of 128.4 million miles (206.7 million kilometers) to a maximum of 154.8 million miles (249.2 million kilometers); average distance from Sun,
141.5 million miles (227.7 million kilometers)
Revolves around Sun once every 687 Earth days
Rotation period (length of day) 24 hours, 37 min, 23 sec (1.026 Earth days)
Poles tilted 25 degrees, creating seasons similar to Earth's
Environment
Atmosphere composed chiefly of carbon dioxide (95.3%), nitrogen (2.7%) and argon (1.6%)
Surface atmospheric pressure less than 1/100th that of Earth's average
Surface winds up to 80 miles per hour (40 meters per second)
Local, regional and global dust storms; also whirlwinds called dust devils
Surface temperature averages -64 F (-53 C); varies from -199 F (-128 C) during polar night to 80 F
(27 C) at equator during midday at closest point in orbit to Sun
Features
Highest point is Olympus Mons, a huge shield volcano about 16 miles (26 kilometers) high and 370
miles (600 kilometers ) across; has about the same area as Arizona
Canyon system of Valles Marineris is largest and deepest known in solar system; extends more than
2,500 miles (4,000 kilometers) and has 3 to 6 miles (5 to 10 kilometers) relief from floors to tops of sur-
rounding plateaus
"Canals" observed by Giovanni Schiaparelli and Percival Lowell about 100 years ago were a visual
illusion in which dark areas appeared connected by lines. The Mariner 9 and Viking missions of the
1970s, however, established that Mars has channels possibly cut by ancient rivers
Moons
Two irregularly shaped moons, each only a few kilometers wide
Larger moon named Phobos ("fear"); smaller is Deimos ('terror"), named for attributes personified in
Greek mythology as sons of the god of war
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