• One of five planets known to ancients; Mars was Roman god of war, agriculture and the state
  • Yellowish brown to reddish color; occasionally the third brightest object in the night sky after the Moon and Venus
Artist's concept of sunrise over Mars from orbit.
Side-by-side comparison of Earth versus Mars.

Physical Characteristics

  • Average diameter 4,212 miles (6,780 kilometers); about half the size of Earth, but twice the size of Earth's Moon
  • Same land area as Earth, reminiscent of a cold, rocky desert
  • 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 128.4 million miles (206.7 million kilometers) to a maximum of 154.8 million miles (249.2 million kilometers); average is 141.5 million miles (227.7 million kilometers)
  • Revolves around the Sun once every 687 Earth days
  • Rotation period (length of day) is 24 hours, 39 minutes, 35 seconds (1.027 Earth days)
  • Poles is tilted 25 degrees, creating seasons similar to those on Earth
Animation of Mars path around the Sun.
The sureface of Mars as seen from Mars Curiousity Rover.


  • 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 of 0 to about 20 mph (0 to about 10 meters per second), with gusts to about 90 mph (more than 100 kilometers per hour)
  • Local, regional and global dust storms; also whirlwinds called dust devils
  • Surface temperature averages minus 64 Fahrenheit (minus 53 Celsius); varies from minus 199 Fahrenheit (minus 128 Celsius) during polar night to 80 Fahrenheit (27 Celsius) at equator during midday at closest point in orbit to Sun


  • 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) of relief from floors to tops of surrounding plateaus
Image of Olympus Mons volcano taken from the Mars Reconnaissance Orbiter.
Photos of Mars as compared to its moons Phobos and Deimos.


  • Two irregularly shaped moons, each only a few miles (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