CRACKING UP: NASA's Phoenix Mars Lander sent back this image of a polygonal pattern in the ground near its landing site in an arctic region called Vastitas Borealis, near the planet's north pole. NASA researchers say the pattern, shown here in approximate color based on violet and infrared light, suggests that subsurface ice has recently undergone seasonal thawing and refreezing. Image: NASA/JPL-Caltech/University of Arizona
Images sent back from the Red Planet by NASA's Phoenix Mars Lander after its picture-perfect Sunday touchdown provide the first close-up views of a barren landscape honeycombed with cracks that may represent the effects of seasonal freezing and thawing of subsurface ice.
NASA mission controllers cheered when Phoenix sent back radio signals confirming that it had successfully completed its 10-month, 422-million-mile (679-million-kilometer) journey to Mars, landing as expected Sunday evening in the arctic plains near the Red Planet's north pole.
The transmission showed that the craft had survived the harrowing "seven minutes of terror" following entry into the Martian atmosphere, in which a combination of friction, parachute drag and bursts from its rockets braked it from a speed of nearly 13,000 miles (21,000 kilometers) per hour to a gentle halt.
Two hours later Phoenix sent back its first snapshots, which corroborated prior observations of the landing area, chosen for its flatness and expected subsurface ice, as flat and barren, devoid of large rocks but riddled with polygon-shaped cracks.
Mission scientists said the cracks, previously observed by orbiting craft, likely represent seasonal thawing and freezing of ice a few inches below the surface.
"We can see cracks in the troughs that make us think the ice is still modifying the surface," Peter Smith, the mission's chief scientist from the University of Arizona, told reporters. "We see fresh cracks. Cracks can't be old. They would fill in."
The images indicate that Phoenix skid a short distance when it set down and confirm that it successfully unfolded its octagonal solar panels to generate power. Phoenix ceased radio transmissions a minute after landing to devote its limited battery power to extending the solar panels.
Mission controllers had cause for celebration: NASA had successfully landed five of six probes on Mars (now six of seven), but this is the first time since Viking 2 in 1976 that the agency set down a craft using rocket thrusters.
During the last attempt nine years ago, Phoenix's sister mission, the Mars Polar Lander—which was to have landed near the planet's south pole—crashed during when its braking thrusters shut down too soon during descent due to faulty sensor readings.
But using air bags to cushion the fall instead of thrusters—the approach used for Mars Pathfinder and the twin rovers Spirit and Opportunity—would have required cutting some of Phoenix's scientific instruments.
NASA said the Phoenix touchdown was nearly flawless. In a minor miscue, its parachute deployed seven seconds too early, which put it 19 miles (30 kilometers) from the spot where mission controllers had intended for it to land.
One of the next major milestones for Phoenix will be the unfolding of its 7.7-foot- (2.3-meter-) long robotic arm, which the probe will use to scrape away the topsoil and collect ice samples. Images sent back yesterday showed that the elbow joint of the robotic arm was still partly covered in a protective sheath that was supposed to unwrap after landing.
Deborah Bass, deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said that the arm's first operations would begin today despite the glitch, according to the Associated Press. "We're going to have to do a little bit of disentangling," she said.