Mars Craft Succeeds in Soft Landing

The 900-pound, three-legged Phoenix lander, which cost $457 million, traveled a circuitous path of 423 million miles over almost 10 months to reach Mars. A rocket-and-parachute landing system -- like that of the Viking landers of 32 years ago -- was chosen because it allowed NASA to better pinpoint the landing location. The system is also a prototype of one that NASA hopes will one day land astronauts on Mars.

The later Mars Pathfinder and the two robot rovers, Opportunity and Spirit, which have been exploring the planet's equatorial region, landed using air bags to cushion the impact. Air bags are not practical for heavier craft such as the Phoenix because the weight of bigger bags reduces the amount of scientific equipment that can be carried.

The Phoenix was targeted at the north polar region because that is where some form of water (in the form of ice) is most likely to be present, and scientists believe that a form of water is necessary for life. They are convinced that surface water flowed on Mars billions of years ago, a conclusion reached by studying geologic features of the Martian landscape. Today, conditions on Mars do not allow for liquid water, in large part because the atmosphere is only 1 percent as dense as Earth's.

In 2002, however, the Mars Odyssey orbiter discovered that large amounts of water ice lay just beneath the surface in the permafrost that covers much of far northern Mars. Scientists say the region, which is notably flat and smooth, may have once been the bottom of a large ocean.

They are also intrigued that the surface shows polygonal patterns remarkably similar to some seen in Antarctica. Scientists speculate that they could be the result of cycles of freezing and thawing.

In addition to its sophisticated cameras, soil retrievers and mini-laboratories, Phoenix carried on its journey a mini-DVD created by the Planetary Society called "Visions of Mars." It holds a library of science fiction stories and art, as well as the names of more than 250,000 people.

The DVD, featuring the likes of Carl Sagan, Arthur C. Clarke and Ray Bradbury, is made of material designed to last for hundreds, if not thousands, of years.