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	Mars At a Glance
	Discovery Known since antiquity Name Roman god of war Average Distance from Sun 141,633,260 miles 227,936,640 km 1.524 Astronomical Units Equatorial Diameter 4,222 miles 6,794 km Mass 0.107 times Earth's mass Length of Day 24 hours, 39 minutes, 35 seconds Length of Year 1.88 Earth years 686.9 Earth days Surface Gravity 0.38 that of Earth (If you weigh 100 pounds, you would weigh about 38 pounds on Mars.) Known Moons 2 (Phobos and Deimos) Compare Planets
	Exploration
	Building on the success of the 1997 Sojourner rover, the Spirit and Opportunity rovers landed on Mars in 2003. Although their planned mission was just 90 Mars days long (about 92 Earth days), both rovers were still operating in 2007. Both found evidence that water had helped shape the Martian landscape in the distant past. Several American and European craft found similar evidence from Mars orbit. More»

Mars inspires speculation like no other world in the solar system. Generations of Earth-bound dreamers have pondered its fiery glow and considered the possibility of life on the "Red Planet." Author H.G. Wells wrote of an attack by invading Martians, and Orson Welles scared unsuspecting Americans by bringing the story to radio.

View in 2009

Scientists, too, have speculated about the possibility of life on Mars. During the 1800s, some leading astronomers thought that an advanced civilization inhabited the planet -- a civilization that built vast "canals" to sustain a dying world. But investigations with increasingly sophisticated ground-based telescopes, followed by the Mariner and Viking missions of the 1960s and '70s, crushed the dreams of grand Martian cities. Mars is too cold and too dry, and its air is too thin, to sustain large organisms.

The Spirit rover’s panoramic view of the Columbia Hills and Gusev Crater.

The farthest of the terrestrial planets from the Sun, Mars orbits between Earth and the asteroid belt. It takes Mars almost twice as long as Earth to orbit the Sun, but a day on Mars lasts almost exactly as long as a day on Earth -- slightly more than 24 hours.

Mars is only about half as big as Earth, but it is enveloped by a thin, cold atmosphere of carbon dioxide and traces of other gases. Temperatures seldom climb to the freezing mark, and can plummet below �0 degrees Fahrenheit (�0 C).

The planet's surface is red because iron in its soil long ago reacted with the tiny amount of oxygen left on Mars to produce rust. Dry riverbeds criss-cross the surface, and several giant volcanoes rise high into the Martian sky. The largest, Olympus Mons, towers 17 miles (27 km) high and covers an area as big as the state of Missouri. Mars also boasts a giant network of valleys that would stretch from New York to Los Angeles. Known as Valles Marineris, it dwarfs the Grand Canyon.

Ice caps cover the Martian poles. When sunlight warms the polar ice caps, water and carbon dioxide vaporize and rush into the air, stirring up tiny grains of dust. The Martian winds carry them around the planet, picking up even more dust. That stirs up dust storms that can last for days or weeks and cover almost all of the planet's surface.

Conditions on Mars don't rule out the possibility of microscopic life. Frozen or even liquid water may exist beneath the Martian soil, perhaps providing a home for living organisms. The Viking landers looked for evidence of such organisms, but their experiments were inconclusive.

The fleet of spacecraft now at Mars -- and more heading out in the coming years -- will try to sniff out signs of life. And scientists are studying meteorites from Mars -- chunks of Martian rock here on Earth -- for signs of ancient Martian life. Scientists continue to debate the results as they continue the long quest to find life on Mars.

View in 2009
Mars climbs into view as a modest orange 搒tar� quite low in the east or southeast at sunrise in late February. As the year progresses, it will pull farther away from the Sun and be visible for more of the night. By late in the year, it will in view for more than half of the night, and will outshine all but two planets and one star. Mars will stage beautiful encounters with Venus in mid-April and again in mid-July.

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This document was last modified: May 04, 2009