Submitted by sondra on Sun, 09/11/2011 - 12:06pm

by Gus Posey, Education Department, The Museum of Flight NASA’s Mars Exploration Rover Opportunity shows “Cape St. Vincent,” one of the many promontories that jut out from the walls of Victoria Crater, Mars. -Photo courtesy of NASA.

Orbiting the sun at an average distance of 140 million miles, the planet Mars is a cold and windy world, wrapped in an insubstantial atmosphere. At all but the lowest elevations, cosmic radiation hammers the Martian surface, unchecked by the planet’s thin sheath of carbon dioxide, nitrogen and argon, transforming the already dangerous landscape into a lethal bath of high-energy particles. And yet, despite the tremendous danger of exploring such a world, Mars remains a tantalizing target for human and robotic explorers, who are only now beginning to unlock the secrets of the red planet.

Since prehistoric times, humans have watched Mars travel across the sky, following an intriguing, elliptical orbit around the sun. The planet’s unmistakable hue, the result of weathered iron oxides on its surface, gave Mars a specific appeal, especially to ancient astronomers still struggling with the mysterious points of light that brightened the night sky. The place of Mars within the mythology of cultures around the world indicates a similar reaction among many different people.

Perhaps as the result of their own sanguinary natures, many ancient people ascribed to Mars the qualities of a wargod, convinced that its rusty glow was a harbinger of conflict and destruction. Astronomers in Babylonia associated Mars with the fiery god Nergal, while the ancient Greeks chose to associate the red planet with their god of war, Ares. The Romans also selected their most bellicose deity, Juno’s son Mars, giving the planet its current name.

Advances in telescopes and observatories provided a slightly more scientific view of Mars, although the planet remained mysterious even in the face of direct observation. In 1877, Italian astronomer Giovanni Schiaparelli used a telescope in Milan to make a detailed map of Mars. During his observations, Schiaparelli recorded long lines running across the planet’s surface. He called these lines canali, an Italian word that means “channels.” As word of his discovery spread, the word was often translated as “canals,” suggesting a Martian intelligence capable of significant engineering.

Incredibly, the mysterious channels were visible to other astronomers, too, and the illusory features were documented several times by reputable scientists, including Percival Lowell, who spent 15 years (1894–1909) studying Mars from his observatory in Flagstaff, Arizona. Lowell published a series of books about Mars and its canals, suggesting a truly advanced intelligence capable of irrigating parched equatorial regions with water from the polar ice caps.

In 1964, following a string of unsuccessful Soviet attempts, the American spacecraft Mariner 4 returned the first detailed pictures of the Martian surface. The pictures showed the cratered landscape of an empty world, a far cry from the maze of canals suggested by Lowell. The pictures changed our concept of Mars, and the idea that life might exist on such a cold, dry planet suddenly seemed unreasonable.

The arrival of the Viking probes in 1976 increased the odds of not finding life on Mars. The first probes to land on the planet’s surface, the two Viking landers were each equipped with a series of experiments designed to identify organic compounds in the Martian soil. Although the results were inconclusive, they suggested that Mars was, in fact, a dead world.

For two decades, the red planet was largely ignored. In 1988, the Soviets attempted their Phobos series, but malfunctioning computers defeated their plans for both orbiting and landing on the planet. NASA’s Mars Observer made the trip in 1992, but, three days before orbital insertion, contact with the probe was lost.

The nearly simultaneous arrival of the orbiting Mars Global Surveyor (MGS) and the Pathfinder lander in 1997 rejuvenated interest in the planet, worldwide attention that was heightened by the deployment of the Sojourner rover, a microwave-sized robot that brought mobility to Martian exploration. Cameras and sensors on both the lander and rover provided invaluable information about the composition of the Martian rocks and atmosphere. These experiments provided the first clues that Mars had once been a warmer, wetter planet.

Between 2001 and 2004, four more spacecraft would travel from Earth to Mars. The Mars Odyssey probe arrived in 2001, searching for signs of water and creating a relay station to Earth for future missions, and the European Space Agency’s Mars Express entered into its operational orbit three years later. NASA’s Mars Exploration Rovers, Spirit (MER-A) and Opportunity (MER-B), arrived on Mars in 2004, and quickly added to the case for water on the planet’s surface, longvanished moisture evidenced by minerals like hematite, an iron oxide that typically forms in the presence of water.

Currently en route to Mars, the Phoenix lander is scheduled to arrive in May 2008. Phoenix is designed to land in the planet’s polar region, collecting ice and soil samples to be analyzed on board. The Phoenix mission differs from that of the rovers, focusing on the search for Martian life.

Other upcoming missions such as the nuclearpowered Mars Science Laboratory (MSL) and the European ExoMars will continue to provide new information about Mars and its unique and hostile environment. According to current NASA plans, the robotic exploration of the red planet will continue for years to come. No specific dates have been set for a human mission to Mars, but current progress suggests that such a project would not be possible until sometime after 2030.

Mars has proven itself to be a celestial target impossible to ignore. Current robotic missions are opening up the planet to scientific scrutiny, constantly adding to our list of questions, even as we find new answers. The eventual arrival of humans on Mars will initiate the next chapter of exploration, finally uniting the curious peoples of Earth with the mysterious red planet

20. Mars - November 15, 20071.7 MB