An Icy Dig in Search of Signs of Life on Mars

The search for life on Mars will resume in earnest next Sunday if NASA's Phoenix spacecraft lands as planned on the icy fringe of the planet's north pole.

Touching down on Mars is a risky business; only about half of the attempts have succeeded. But assuming that Phoenix does arrive upright and in one piece, the craft will begin digging into the soil and ice beneath it to look for signs that life once existed -- or could have existed -- in the barren landscape.

Phoenix's study of the northern permafrost "takes the next step in Mars exploration by determining whether this region, which may encompass as much as 25 percent of the Martian surface, is habitable," said Peter Smith of the University of Arizona, the mission's principal investigator.

In particular, he said, Phoenix will try to determine whether the ice holds any carbon-based organic material -- a component of all known life -- and whether the ice ever melted. "As we dig down, we hope to find signs that the soil has mixed with the ice, which means there was once liquid water," Smith said. "And if we find organics, that will be a major discovery."

Phoenix is scheduled to land about 7 p.m. Eastern time on Sunday, joining NASA's robotic rovers Spirit and Opportunity on the Martian surface. But its descent will be very different. When the twin rovers touched down in 2003, they were surrounded by air bags that cushioned their landings and sent them bouncing across the surface. Once they stopped, the bags deflated and the rovers emerged.

Phoenix will descend more traditionally, slowed by a parachute and its thrusters in much the same manner as the Mars Polar Lander, which crashed on descent in 1999. Phoenix has been modified to improve its chances, but many space scientists and engineers will be holding their breath Sunday evening as it descends. It will take about 15 minutes for its radio signal to reach Earth with the news, either that it made it safely or that another spacecraft has been destroyed in the attempt.

Also unlike the two mobile and remarkably long-lived rovers, Phoenix is designed to plant itself in one spot and start digging with a Canadian-built robotic arm as much as three feet deep into the soil and, scientists hope, through subsurface layers of ice. The lander has a set of miniature but sophisticated chemistry labs to analyze the soil and ice that the robotic arm pulls aboard Phoenix.

The spacecraft is aiming for a landing farther north than any other on Mars, in an area with ice and perhaps signs of once-liquid water. NASA's search for life in the solar system is based on the theme of "follow the water," on the assumption that life needs water to exist.

Although the temperatures will be well below freezing on the surface -- minus-28 to minus-100 degrees Fahrenheit -- scientists think the temperatures, and the ice, could be warmer below the surface and may once have even been liquid. The region is low and flat, and some theorize that it may have held an ocean long in the past.

The ice also shows polygon patterns remarkably similar to some found in Antarctica. Scientists speculate that they could be the result of cycles of freezing and thawing.

The $457 million Phoenix spacecraft has traveled a long and circuitous path, and not just on its journey of 422 million miles through space. Phoenix uses equipment built for a spacecraft that was supposed to be launched in 2001, which was scratched because of the Polar Lander's crash.

When in 2002 NASA's Mars Odyssey orbiter detected substantial amounts of water ice lying just beneath the surface, however, a reconfigured Phoenix was selected to fly to Mars and dig for the ice in the northern polar region. It will also set up a $37 million Canadian weather station.