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The red planet Mars has inspired wild flights of imagination over the to be the source of hostile invaders of Earth, the home of a dying civilization, or a rough-and-tumble mining colony of the future, Mars provides fertile ground for science fiction writers, based on seeds planted by centuries of scientific observations.

We know that Mars is a small rocky body once thought to be very Earth-like. Like the other "terrestrial" planets - Mercury, Venus, and Earth - its surface has been changed by volcanism, impacts from other bodies, movements of its crust, and atmospheric effects such as dust storms. It has polar ice caps that grow and recede with the change of seasons; areas of layered soils near the Martian poles suggest that the planet's climate has changed more than once, perhaps caused by a regular change in the planet's orbit. Martian tectonism - the formation and change of a planet's crust - differs from Earth's. Where Earth tectonics involve sliding plates that grind against each other or spread apart in the seafloors, Martian tectonics seem to be vertical, with hot lava pushing upwards through the crust to the surface. Periodically, great dust storms engulf the entire planet. The effects of these storms are dramatic, including giant dunes, wind streaks, and wind-carved features.

Scientists believe that 3.5 billion years ago, Mars experienced the largest known floods in the solar system. This water may even have pooled into lakes or shallow oceans. But where did the ancient flood water come from, how long did it last, and where did it go?

In May 2002, scientists announced the discovery of a key piece in the puzzle: the Mars Odyssey spacecraft had detected large quantities of water ice close to the surface - enough to fill Lake Michigan twice over.

The ice is mixed into the soil only a meter (about 3 feet) below the surface of a wide area near the Martian south pole.

Many questions remain. At present, Mars is too cold and its atmosphere is too thin to allow liquid water to exist at the surface for long. More water exists frozen in the polar ice caps, and enough water exists to form ice clouds, but the quantity of water required to carve Mars' great channels and flood plains is not evident on - or near - the surface today. Images from NASA's Mars Global Surveyor spacecraft suggest that underground reserves of water may break through the surface as springs. The answers may lie deep beneath Mars' red soil.

Unraveling the story of water on Mars is important to unlocking its past climate history, which will help us understand the evolution of all planets, including our own. Water is also believed to be a central ingredient for the initiation of life; the evidence of past or present water on Mars is expected to hold clues about past or present life on Mars, as well as the potential for life elsewhere in the universe. And, before humans can safely go to Mars, we need to know much more about the planet's environment, including the availability of resources such as water.

Mars has some remarkable geological characteristics, including the largest volcanic mountain in the solar system, Olympus Mons (27 km high and 600 km across); volcanoes in the northern Tharsis region that are so huge they deform the planet's roundness; and a gigantic equatorial rift valley, the Valles Marineris. This canyon system stretches a distance equivalent to the distance from New York to Los Angeles; Arizona's Grand Canyon could easily fit into one of the side canyons of this great chasm.

Mars also has two small moons, Phobos and Deimos. Although no one knows how they formed, they may be asteroids snared by Mars' gravity.


Mars: Facts & Figures

Discovered By: Known by the Ancients

Date of Discovery: Unknown


Average Distance from the Sun

Metric: 227,936,640 km

English: 141,633,260 miles

Scientific Notation: 2.2793664 x 108 km (1.523662 A.U.)

By Comparison: 1.524 x Earth


Perihelion (closest)

Metric: 206,600,000 km

English: 128,400,000 miles

Scientific Notation: 2.066 x 108 km (1.381 A.U.)

By Comparison: 1.404 x Earth


Aphelion (farthest)

Metric: 249,200,000 km

English: 154,900,000 miles

Scientific Notation: 2.492 x 108 km (1.666 A.U.)

By Comparison: 1.638 x Earth


Equatorial Radius

Metric: 3,397 km

English: 2,111 miles

Scientific Notation: 3.397 x 103 km

By Comparison: 0.5326 x Earth


Equatorial Circumference

Metric: 21,344 km

English: 13,263 miles

Scientific Notation: 2.1344 x 104 km


Metric: 163,140,00,000 km3

Scientific Notation: 1.6314 X 1011 km3

By Comparison: 0.150 x Earth



Metric: 641,850,000,000,000,000,000,000 kg

Scientific Notation: 6.4185 x 1023 kg

By Comparison: 0.10744 x Earth



Metric: 3.94 g/cm3

By Comparison: 0.714 x Earth

Surface Area

Metric: 144,100,000 km2

English: 89,500,000 square miles

Scientific Notation: 1.441 x 108 km2

By Comparison: 0.282 x Earth


Equatorial Surface Gravity

Metric: 3.693 m/s2

English: 12.116 ft/s2

By Comparison: If you weigh 100 pounds on Earth, you would weigh 38 pounds on Mars.


Escape Velocity

Metric: 18,072 km/h

English: 11,229 mph

Scientific Notation: 5.02 x 103 m/s

By Comparison: Escape velocity of Earth is 25,022 mph.


Sidereal Rotation Period (Length of Day)

1.026 Earth days

24.62 hours

By Comparison: Earth's rotation period is 23.934 hours.


Sidereal Orbit Period (Length of Year)

1.8807 Earth years

686.93 Earth days

Mean Orbit Velocity

Metric: 86,871 km/h

English: 53,979 mph

Scientific Notation: 24,130.9 m/s

By Comparison: 0.810 x Earth


Orbital Eccentricity


By Comparison: 5.59 x Earth


Orbital Inclination to Ecliptic

1.8 degrees

Equatorial Inclination to Orbit


Orbital Circumference

Metric: 1.366,900,000 km

English: 849,400,000 miles

Scientific Notation: 1.3669 x 109 km

By Comparison: 1.479 x Earth


Minimum/Maximum Surface Temperature

Metric: -87 to -5 C

English: -125 to 23 F

Scientific Notation: 186 to 268 K

Atmospheric Constituents

Carbon Dioxide, Nitrogen, Argon

Scientific Notation: CO2, N2, Ar

By Comparison: CO2 is responsible for the Greenhouse Effect and is used for carbonation in beverages.

N2 is 80% of Earth's air and is a crucial element in DNA. Ar is used to make blue neon light blubs.

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