NASA's Phoenix spacecraft launched Saturday morning from Cape Canaveral, Fla., on a 10-month journey to the north pole of Mars, where it is expected to be the first craft to taste the water of another planet.
The Delta II rocket carrying the 7-foot-tall lander lifted off at 5:26 a.m. on a scheduled 423million-mile journey that should deliver Phoenix to the Martian surface on May 25.
"We certainly are excited about launching, but we are still concerned about our actual landing, the most difficult step of this mission," Smith said.
NASA has a mixed record with Mars missions. Its twin rovers Spirit and Opportunity have been resounding successes, still going strong after 3 1/2 years on the surface.
But the last mission to the polar region, Mars Polar Lander, was lost on arrival in 1999.
If this mission unfolds as planned, the lander will parachute to the Red Planet's surface, using its descent engines to slow itself to about 5 mph. Once on the ground, it will unfurl its power-generating solar panels and extend its 7.7-foot robotic digging arm, the key component of the $420-million mission.
A scoop on the arm will dig down to a layer of water ice — thought to lie within 3 feet of the surface — that the Mars Odyssey spacecraft detected from orbit in 2002. A drill-like tool was added to the scoop after scientists realized that the ice on Mars could be much harder — more like cement — than ice on Earth.
Samples of soil and ice collected by the robotic arm will be transferred onboard for analysis. Phoenix carries eight tiny ovens that will heat the samples in search of organic compounds that could indicate past or present biological processes. Each oven will be used only once to avoid contamination.
NASA has tried to keep expectations low, asserting that Phoenix is not searching for life, merely trying to understand the water story. "Water is central to every type of study we will conduct on Mars," Smith said.
NASA learned to manage expectations with the Viking missions to Mars in 1976. The public, its appetite whetted by generations of science fiction writers envisioning Martians plying canals like Venice boatmen, waited excitedly for news of the discovery of life, only to have the spacecraft report a sterile, lifeless world.
That disappointment haunted the Mars program for decades. Only in recent years, with such discoveries as large subterranean deposits of ice and tantalizing evidence of surface flows, has there been renewed interest in Mars.
Some scientists now believe that the Viking landers either were searching in the wrong places or weren't equipped to look for the right clues.
Even the optimists acknowledge that Mars is, and possibly always has been, too hostile an environment for complex life forms. But scientists no longer rule out the possibility that some rudimentary forms of life could once have existed, and may still, possibly in some watery underground environment heated by the planet's interior.
In contrast to Earth and Venus, with their substantial internal sources of heat-causing volcanic activity, Mars' volcanoes appear to be long dead, a kind of "warm corpse," researchers say.
Scientists believe that Mars has gone through three ages, starting with what they call the Noachian, the first billion years and the most livable era, when the planet may have had a much warmer surface with running streams and possibly rain. The Hesperian era came next, a 500-million-year period when geologic activity slowed and water pooled underground.
The current period is referred to as the Amazonian, a 2- to 3-billion-year era during which the surface became desiccated and the atmosphere grew thin.
Scientists hope that scientific instruments aboard Phoenix will fill out the story.
In a space mission, as with air travel, the launch and landing are the most dangerous events. Phoenix's landing site is on an arctic plain called Vastitas Borealis, which is similar in most respects to central Greenland or northern Alaska.
The craft is expected to touch down in a shallow valley 30 miles wide and 800 feet deep.
The site was chosen after an early favorite turned out to be covered with large rocks. If one of the lander's three legs came to rest on one, it could tip precariously.
During Mars' winter, when temperatures can drop to minus-199, the area is covered with carbon dioxide frost and ice. So the craft will land in late spring, when the surface is more typical of Mars, covered with thick dust.
Winter's harshness is one reason Phoenix will not contend with the rovers for longevity. The lander will become shrouded in carbon dioxide ice, imposing a short lifetime of about 90 Martian days for the mission.
The spacecraft was designed and built by Lockheed Martin Space Systems Co. and is managed by NASA's Jet Propulsion Laboratory.