Mars

Mars is the fourth planet from the center of the solar system, orbiting the Sun once every 687 (Earth) days at a mean distance of 141 million mi (227 million km). Called the "red planet" for its distinct orange-red color, Mars has been the object of intense interest for over a century. Popularly regarded as a possible source of life, Mars was thought to be barren after the Viking spacecraft landed on it in 1976 and found no evidence of living organisms. But interest in Mars as at least an ancient host of life resurged in the 1990s with the claim of fossilized microbes in meteorites from Mars, and pictures from the 1997 Pathfinder mission that suggested water once swept across the Martian surface.

Mars has numerous earthlike features. There are large, extinct volcanoes dotting its surface, eroded channels where water once flowed freely, and ice caps covering its poles that look very much like Earth's polar regions. But, the thin Martian atmosphere is made mainly of carbon dioxide. Although Mars may now be a cold, dead world, the variety of features on its surface suggests a complex and fascinating past.

Perhaps we will learn more about this fascinating planet when the new NASA Odyssey mission and the two planned NASA Mars Exploration Rover missions launch and reach Mars in the next few years.