Test Your Mars IQ

Not only is Mars' atmosphere virtually devoid of oxygen, but the surface atmospheric pressure is less than 1 percent of Earth's - effectively a vacuum. The thin atmosphere affords virtually no protection from the sun's deadly ultraviolet radiation, and there's no global magnetic field to divert charged particles.

The Martian year equals 687 Earth days. Mars' poles are tilted 25 degrees, creating seasons similar to Earth's but twice as long.

The minimum distance between Earth and Mars is 34.9 million miles, or about three light-minutes. Thus, the minimum round-trip travel time at the speed of light is six minutes. (When the distance between the two planets is widest, that figure would amount to about 45 minutes.)

The Martian moons Phobos (Greek for "fear") and Deimos (Greek for "terror") measure only a few miles wide and are named after the mythological sons of Mars, the god of war.

The surface temperature varies from 199 below zero F during polar night to 63 degrees F at the Martian equator during midday at the closest point in orbit to the sun.

Mars' average diameter is 4,217 miles, about half that of Earth but twice the diameter of Earth's moon. Because of Mars' lighter density and the way diameter translates into volume, the planet's mass is a tenth of Earth's mass.

Carbon dioxide makes up more than 95 percent of the Martian atmosphere. The other ingredients include nitrogen (2.7 percent), argon (1.6 percent) and just a trace of oxygen.

Olympus Mons is a 16-mile-high volcano that covers about the same surface area as the state of Arizona. Mars also has the largest and deepest known canyons in the solar system, measuring as much as 2,500 miles long and six miles in relief from the canyon floor to the surrounding plateaus.

Gravity on the Martian surface would be 38 percent of Earth's gravity, due to factors such as density and radius.

The Martian day is called a "sol," and lasts 24 hours, 37 minutes, 23 seconds.