Fewer than half the missions that have attempted landings on Mars have survived, so tension is rising at NASA's Jet Propulsion Laboratory as the Phoenix spacecraft closes in for a landing today on the planet's north pole, where it will be the first to sample the water of another planet.
"This is not a trip to grandma's house. Putting a spacecraft safely on Mars is hard and risky," said Ed Weiler, associate administrator for NASA's science mission directorate in Washington.
The spacecraft was named Phoenix -- a reference to the mythical bird that rises from its own ashes -- because it replaces another craft, the Mars Polar Lander, that was lost as it attempted a landing in 1999. The latest updates on the spacecraft have eased some of the anxiety among the legion of scientists involved.
"There is always tension with these things," said project manager Barry Goldstein. "You work on something for five years, and then you hold your breath for the final seven or 14 minutes" during touchdown. "But things have been going extremely well so far," he added.
The landing, if successful, would be the first on Mars since the NASA rovers Spirit and Opportunity arrived in 2004.
The lander is scheduled to parachute to the planet's surface and touch down at 4:54 p.m. PDT. If the entry/descent/landing communications links work correctly, Goldstein said, managers at JPL in La Canada Flintridge should know within two minutes whether the craft is safely on the ground. Two hours later, scientists will find out whether the solar panels that will power the lander on Mars have opened successfully.
One of the greatest dangers is landing on rocks large enough to tip over the robotic lander, or that prevent the solar panels from unfurling.
To reduce that danger, mission managers have used the Mars Reconnaissance Orbiter to snap hundreds of pictures of the landing site, a 30-mile-wide arctic plain called Vastitas Borealis.
"This is one of the least rocky areas on all of Mars," said Ray Arvidson of Washington University, who chairs Phoenix's landing site working group. "We are confident that rocks will not detrimentally impact the ability of Phoenix to land safely."
Phoenix also is landing in the Martian spring, so it should not encounter large mounds of ice on the ground.
"There may be outcrops," Goldstein said. But they shouldn't present serious problems.
The key element of the $420-million mission is a 7.7-foot robotic arm outfitted with a scoop to dig through a layer of dust to reach the ice below. Because the ice is expected to be as hard as concrete, the robotic arm will use a drill-like tool to break off shards.
The motto of scientists hunting for life on other planets has been "Follow the water," because water is considered a fundamental medium that allows biological processes to begin.
The water at the north pole will be locked up in the ice; therefore Phoenix carries eight tiny ovens that will heat the samples of soil and ice to search for organic compounds that could indicate past or present biological processes.
Goldstein said that presuming everything goes according to plan, operators on Earth will deploy the robotic arm on Tuesday. After that, it will begin digging slowly into the soil.
It could be July or later before Phoenix's excavations reach the ice.