Mars: Fourth planet from the Sun

Average distance from the Sun: 1.524 AU (227.94 million km)
Orbital period (Length of Year): 686.98 Earth days
Rotational period (Length of Day): 24.5 Earth hours
Orbital inclination: 1.85 deg
Average orbital speed around the Sun: 24.13 km/s
Diameter: 6,787 km
Axial inclination: 25 deg
Mass: 6.42 x 10 ^ 23 kg (0.11 Earth mass)
Relative surface gravity (Earth = 1): 0.377
Maximum temperature: -33 deg C (-27 deg F)
Minimum temperature: -83 deg C (-117 deg F)
Atmosphere: Carbon dioxide, nitrogen, argon
Albedo: 0.15
Number of satellites: 2 (Phobos and Deimos)

Mars, named for the Roman god of war, is the nearest planet whose orbit is outside that of the Earth. It is often called the Red Planet, its color due to iron oxide (otherwise known as rust) in the soil.

Mars has long been a planet of interest and intrigue. The 19th century Italian astronomer Giovanni Schiaparelli made many telescopic observations of the planet. He noted the presence of "canali", or "channels", on the surface. The term was then improperly translated as "canals", implying an artificial origin. But neither canals nor their Martian architects have ever been found.

From Earth, we can see that there are seasons on Mars. During the Martian winter in the northern hemisphere, there is a large polar cap of frozen carbon dioxide. By Martian summertime, that polar cap almost disappears as the more equatorial regions darken. In the past, one explanation put forth was that Martian vegetation grew and flourished in spring. But the most acceptable theory today states that at the end of the northern hemisphere's spring, a global dust storm begins, covering the surface with light dust. The high winds then uncover the darker regions below. The southern hemisphere goes through a similar cycle half a Martian year later.

Details of the Martian surface were first recorded by Mariner 6. Most noticeable was the vast number of large and small craters; Mars looked like another moon! Mariner 9 showed that Mars has a structure of its own with only the older portions being similar to the lunar surface. Of particular importance is evidence that water may have shaped some Martian canyons and snake-like valleys. Mars also has volcanoes, one of the largest being Olympus Mons Ð 600 kilometers (370 miles) across its base and about 25 kilometers (15.5 miles) high.

Two United States Viking spacecraft reached Mars in the summer of 1976. Each craft consisted of an orbiter and a lander. While the orbiter photographed and analyzed the surface, the landers sampled the reddish soil to determine whether there was life on Mars. Results from these missions confirmed earlier observations. "River channels" and the effect of flowing surface material indicated the possible past presence of water. Mars was found to have a pink sky. The residues of the polar caps are believed to be water ice, since summer temperatures are too high for frozen carbon dioxide. No life forms were discovered.

There are several current missions to Mars.  Two rovers, named Spirit and Opportunity will land on Mars in January of 2004, after spending about 6 months in transit.  The primary mission objective is to investigate a wide range of rocks and soil that hold clues to past water activity on Mars.  The rovers will land on the surface of Mars by bouncing on a cushion of surrounding airbags.  Each mission will be operational for 90 days on the surface.

In December of 2003, Mars Express, a joint mission between the European Space Agency and NASA, will reach Mars.  Mars Express features an orbiter and a lander.  The lander’s name is Beagle 2, and it will make soil and rock measurements for 185 days.  Instruments on the orbiter will map the composition of Mars’ surface and atmosphere.  The orbiter will also search for water on mars and take detailed images of the surface.

The two Martian moons revolve so rapidly around Mars that they stand out in the Martian sky. Phobos, the closer moon, goes around Mars faster than Mars rotates. Thus, while everything else in the Martian sky appears to rise in the east and set in the west (as on Earth), Phobos rises in the west and sets in the east, appearing to move opposite to everything else in the sky.

Though Deimos does revolve slower than Mars rotates, its speed is so comparable it that stays in the Martian sky for more than two and a half Earth days from moonrise to moonset.

Information Source:  http://www.moreheadplanetarium.org/index.cfm