We've already seen water ice on Mars. NASA's Phoenix lander will reach out and touch it.
- By Charles Petit
- Air & Space magazine, August 2007
(Page 2 of 5)
Once Phoenix is on the ground, two circular solar panels will extend from its sides and open like Chinese fans to provide power. A column of delicate tubing will rise like a stalk, with a stereo camera on top for panoramic photography. From the lander’s flat deck will extend a robotic arm equipped with small cameras, microscopes, and, most important, a shovel and small electric grinder—the same kind used for sculpting ice. Articulated like a backhoe, the arm can in principle dig a trench about two feet deep, at least in soft ground. The whirring grinder is designed to break frozen ground into manageable bits for the shovel to scrape up. Nobody expects the grinder to penetrate more than a fraction of an inch into the permafrost, which will be deep-frozen to about –130 degrees Fahrenheit.
Mission scientists believe the lander will find ice mixed with the soil just below the dusty surface. And some researchers, like Ray Arvidson of Washington University in St. Louis, a co-investigator with the robotic arm science team, expect to see, on close inspection, patches of hard, blue ice peeking through.
All previous Mars landing missions have been dusty affairs. This could be the first one to make mud. After the arm collects the frozen samples, they’ll be placed in miniature ovens and heated for study. A suite of instruments (see “Land, Look, Dig, Cook,” p. 55) will inspect the soil and meltwater for organic molecules and other signs of biochemical activity. Ratios of hydrogen and deuterium (an isotope of hydrogen) should tell scientists whether the ice in the permafrost came from ancient groundwater or fell as rain. Meanwhile, a meteorology package provided by Canada will take weather readings; the pressure gauge comes from Finland, the wind sensor from Denmark. Phoenix’s cameras will inspect the shallow trench dug by the arm, looking for layering or variations in chemistry that would indicate whether liquid water existed at the site. The planet’s orbit and axial tilt change in cycles lasting tens of thousands to millions of years. That means there may have been epochs with warmer summers during which water persisted on or near the surface within the past 100,000 years. Phoenix will help scientists piece together that story.
The “nominal” mission—the length of time needed to achieve the major scientific goals—is three months. That’s how long the sun will stay high enough for the spacecraft to produce sufficient electrical power to run its robotic arm and shovel. Plans are to go through seven digging cycles, each lasting about eight Martian days, or sols (a Martian day is 37 minutes longer than an Earth day). By December, as the sun drops too low to keep the batteries charged, the spacecraft should begin dying. By the time the sun rises again in the Martian spring, the craft “may be buried up to its deck in carbon dioxide snow,” or perhaps frost, Smith says.
At the tucson operations center last November, things were fairly quiet. The spacecraft itself was still in a clean room at the Lockheed Martin Space Systems plant in Littleton, Colorado, where it was built. Here in Tucson a young engineer, Lori Harrison, was attaching a set of instruments called TEGA, for Thermal Evolved Gas Analyzer, to a full-size engineering test version of the lander sitting on a simulated Martian landscape. Better to discover any glitches with the instruments’ operation now instead of next year on the surface of Mars.
Smith showed me into a room equipped with computer consoles where data from the mission will be analyzed. Spread on a large table were glossy photos, blown up to the size of hall carpets, showing the Phoenix team’s first choice for a landing zone. They came courtesy of another NASA spacecraft, the Mars Reconnaissance Orbiter, whose most powerful camera, called HiRISE, was also built at the University of Arizona.
Smith is a Tucson native and has spent most of his career at this school, which has one of the best planetary science departments in the world. He led the team that built the camera for the Mars Pathfinder lander, which, with its little rover Sojourner, kicked off the modern era of Martian exploration in 1997. Since then Smith has had a hand in HiRISE and other Mars cameras developed at Arizona. He also was a co-investigator for the descent camera on the European Huygens probe, which in January 2005 returned broad panoramas of the surface of Saturn’s haze-shrouded moon Titan (see “219 Minutes on Titan,” Oct./Nov. 2005).
Not all his memories are happy. In 1999, Smith sat tensely watching monitors at JPL as the Mars Polar Lander, whose stereo lander camera his group had built, entered the atmosphere in preparation for a touchdown near the planet’s south polar icecap. It was never heard from again. “We just sat and sat, and it got quieter and quieter,” Smith recalled. Engineers later discovered a flaw in the spacecraft’s software that shut off the craft’s landing rocket, causing it to go into a free-fall high above the surface. Four years later, a British lander named Beagle also vanished on arrival—one of Smith’s devices was on that one too. “Getting to Mars is difficult,” he says slowly, leaning forward in his chair. “About 50 percent of the missions fail.”