For a decade, the US space program’s mantra for Mars has been “follow the water.” Now, the Phoenix Mars Lander is poised to reach out and touch it.

On Sunday, NASA’s latest Mars mission is scheduled to touch down on the red planet, marking a turning point in the program. Previous missions have gathered a wealth of data on water’s role in shaping the climate and landscape of ancient Mars. The Mars Phoenix Lander, by contrast, is looking for water’s presence and effects today.

Water is a key ingredient for organic life. While the lander – a chemistry lab on a platter – is not equipped to look for life directly, it is packed with hardware to scratch beneath the surface into Mars’s version of Arctic permafrost. One major goal: to see if this area of the planet could be a suitable habitat for simple organisms.

“The polar regions are where we can understand recent processes, recent climate change, and potential habitability,” says Peter Smith, a senior research scientist at the University of Arizona and the mission’s lead investigator.

Previous missions have landed in areas carved by ancient flows and laden with water-formed rocks and minerals, he explains.

For instance, the team working with the rovers Spirit and Opportunity far to the south of the Phoenix landing site reported Friday that Spirit has uncovered deposits of virtually pure silica. Silica forms as volcanic steam or hot water wells up through the crust. The deposits are similar to those found in Yellowstone National Park, the team says. On Earth, such deposits often bear fossil remains of microbes. The results appear in Friday’s edition of Science.

Before the Phoenix Mars Lander can tell scientists anything, though, the craft must pass through what project manager Barry Goldstein at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., calls “seven minutes of terror.”

Mars has proven to be an unforgiving target. And this mission “is no trip to grandma’s for the weekend,” says Ed Weiler, who heads the Space Missions Directorate for the National Aeronautics and Space Administration. For the engineers and scientists supporting the lander here on Earth, the seven minutes of nail-biting will coincide with a complex set of small explosions, motor firings, and maneuvers the system must execute with exquisite timing to deposit the 900-pound lander safely on the surface.

During the 14 minutes before landing, some 26 “pyrotechnic events” are scheduled to occur that do everything from separating Phoenix from the spacecraft that carried it through space to shedding the heat shield protecting it during its fiery plunge through the Martian atmosphere.

At one point during the descent, the lander’s thrusters must scoot the craft sideways to try to ensure that it won’t get tangled up in its parachute as it touches down. The final 40 seconds of the descent rely on a dozen small motors, each firing in pulses, to ease the lander’s three legs onto the surface. Then, after a 20-minute wait for the dust to settle, the craft will deploy its solar panels. Folks at JPL won’t get confirmation of that process until 90 minutes after touchdown. With a “panels deployed” signal, it’s truly high-five time.

The lander carries an array of instruments designed to, in effect, taste and smell the Martian soil, says Sam Kounaves, a Tufts University chemist and member of the science team. A sterilized mini-backhoe will dig up soil samples near the lander to a depth of about 20 inches. That should be deep enough to bring up water-ice that had been detected previously by Mars orbiters. Estimates are that the soil at this spot contains from 30 to 60 percent water-ice.

Soil samples then get directed to each of two microscopes on the lander, and to eight small, use-it-once furnaces. These furnaces can reach temperatures of up to 1,000 degrees Celsius (1,832 degrees Fahrenheit). By measuring temperatures at which materials vaporize in the heat and analyzing the gases created, the lander’s instruments can give scientists a bead on the compounds in the soil.

Researchers are looking in particular for organic compounds that could represent building blocks for life. In addition, Dr. Kounaves says, he and his colleagues will be looking for inorganic compounds that could serve as food for simple organisms. If a smorgasbord is there, “then its more probable that life might have been there as well,” he says.

In addition, as the scoop works its way down, researchers will analyze samples at each depth for evidence of changes in the area’s recent climate – manifest in the presence or absence of salts among the soil’s constituents. And the lander hosts several cameras plus a weather station that will track local conditions throughout the 90-day (Martian time) mission, during which the seasons will shift from late spring to midsummer.

Although the mission isn’t designed to hunt for life directly, its hardware is suited to an experiment that could answer a key related question: Does Mars’s red hue come from oxidation based on inorganic chemistry, or does the oxidation have a biological origin?

Since the days of the two Viking lander missions, which found no evidence for life at their sites, many scientists have held that inorganic compounds are responsible for oxidizing the surface. But last year, a team led by Dirk Schulze-Makuch at Washington State University proposed that cellular life, with hydrogen peroxide as part of an organism’s cell fluids, could also do the trick.

Hydrogen peroxide – popular as a hair bleach with the surfing set in the 1960s – is present in terrestrial organisms, such as Bombardier beetles, Dr. Schulze-Makuch explains. Hydrogen peroxide attracts water, so creatures with a significant amount in their cellular fluids might be able to absorb water vapor out of the atmosphere, instead of requiring liquid water. The compound might also serve as an antifreeze to help carry simple organisms through the Martian winter.

But hydrogen peroxide can break down easily, so it would need a stabilizing compound to hold it together. And the hardware on Phoenix is up to the task of detecting it. The detection of any one of several possible stabilizers wouldn’t be the smoking gun for life, he concedes. “But it would be strongly supportive.”