Mars at a Glance

Average diameter 6,780 kilometers (4,212 miles); about half the size of Earth, but twice the size of Earth's Moon
Mass 1/10th of Earth's; gravity only 38 percent as strong as Earth's
Density 3.9 times greater than water (compared to Earth's 5.5 times greater than water)
No planet-wide magnetic field detected; only localized ancient remnant fields in various regions

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 206.7 million kilometers (128.4 millions miles) to a maximum of 249.2 million kilometers (154.8 million miles); average distance from the Sun 227.7 million kilometers (141.5 million miles)
Revolves around Sun once every 687 Earth days
Rotation period (length of day) 24 hours, 39 min, 35 sec (1.027 Earth days)
Poles tilted 25 degrees, creating seasons similar to Earth's

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 -53 C (-64 F); varies from -128 C (-199 F) during polar night to 27 C (80 F) at equator during midday at closest point in orbit to Sun

Highest point is Olympus Mons, a huge shield volcano about 26 kilometers (16 miles) high and600 kilometers (370 miles) across; has about the same area as Arizona
Canyon system of Valles Marineris is largest and deepest known in solar system; extends morethan 4,000 kilometers (2,500 miles) and has 5 to 10 kilometers (3 to 6 miles) relief from floors totops of surrounding plateaus

Two irregularly shaped moons, each only a few kilometers wide. Larger moon named Phobos ("fear"); smaller is Deimos ("terror"), named for attributes personi-fied in Greek mythology as sons of the god of war.