NASA's Mars Phoenix lander has unfurled its solar panels and transmitted its first images of the planet's northern plains back to Earth, revealing a remarkably flat and strangely patterned landscape.

Throughout the images, there is ample evidence of the "polygons" that orbital images hinted should be present at the landing site.

The polygons are defined by trough-like boundaries, likely created by the repeated expansion and contraction of subsurface ice. As seen through Phoenix's eyes, the polygons give the landing site a quilt-like appearance, characterised by low bumps and shallow dips.

All the pictures seen so far show an area that is outside the "digging area" of the lander's robotic arm, but principal investigator Peter Smith of the University of Arizona in Tucson, US, expressed optimism that the interesting features evident in the terrain would continue closer to the lander, where Phoenix can scoop samples for detailed examination.

"This is a scientist's dream," said Smith.

Wind-scoured site

If Phoenix manages to sample a trough, it will probably find traces of "a complex history" that could relate to the movement of water vapour to and from an icy layer thought to lie just below the soil's surface, Smith told New Scientist.

Phoenix is designed to dig down to the ice and search for traces of organic residue that might indicate whether this part of Mars could have been habitable in the past.

Smith also noted that the soil around the lander looks granular, "like gravel", which suggests a wind-scoured place where the fine red dust - so common at other landing sites - has been carried away on the Martian breeze.

In one image, a bright white object is clearly visible in the distance protruding towards the horizon line (see image below right).

Team members did not reveal their guesses as to what the object could be, but there is speculation here that it could be the lander's protective backshell, which separated from Phoenix along with its parachute less than a minute before touchdown. The object will likely be imaged at higher resolution and at different Sun angles, which may help solve the mystery.

Critical deployment

The images began streaming down at about 1900 PDT on Sunday (0300 GMT on Monday), courtesy of the Mars Odyssey spacecraft, which made a return pass over Phoenix's landing site after earlier relaying news of the lander's safe arrival at 1653 PDT (0053 GMT on Monday).

After deploying its solar panels and stereo camera approximately 15 minutes after landing, Phoenix executed a pre-programmed sequence of images designed to help engineers assess its health.

The pictures clearly show the unfolded solar panels and one foot of the lander planted firmly on the Martian surface. The images sparked a round of cheering as they flooded into the mission control area of NASA's Jet Propulsion Laboratory in Pasadena, California, US.

The solar arrays are nearly as critical to the success of the mission as the landing itself. Without them, the spacecraft could only survive an estimated 34 hours on battery power. Engineers were elated when they saw the dust-free condition of the solar arrays, said Ed Sedivy, Phoenix programme manager for Lockheed Martin, which built the spacecraft.

Maximise power

The lander's own onboard instruments indicate that it is sitting nearly level, with a tilt of no more than 0.25°. Had Phoenix ended up with a significant tilt in the wrong direction, it would have reduced the amount of solar power available to science experiments.

Data relayed to Earth during the spacecraft's descent indicate it performed a "pirouette" manoeuvre, as planned, so that its panels opened along an east-west axis to maximise power.

"We rehearsed all of the problems, and none of them occurred," Phoenix project manager Barry Goldstein told reporters, clearly relieved at what appears to have been a remarkably smooth landing.

One notable divergence from textbook perfection was the opening of the lander's parachute 6.5 seconds later than anticipated. This ultimately caused Phoenix to touch down about 25 kilometres eastward of its expected destination, at a site near the outer edge of its projected landing ellipse.

While this leaves engineers with a puzzle to solve about why the chute deployed late, it is not expected to affect the science that Phoenix will return, because different points within the landing ellipse are expected to be virtually identical to one another.

Human missions

The landing marks NASA's sixth success in seven attempts to land on Mars since Viking I touched down in July of 1976. But this impressive success rate belies genuine concerns that NASA managers had about the pulse thruster landing system that Phoenix employed during its final descent.

Prior to this evening, NASA's recent successes – including Mars Pathfiner in 1997 and the two Mars Exploration Rovers in 2004 – have all bounced to the surface of the Red Planet encased in inflatable air bags.

Phoenix and future missions, including the more ambitious Mars Science Laboratory, were designed to land with thrusters, considered a must for heavier payloads – and for any future attempt to send astronauts on Mars.

"The way we're going to land humans on Mars is with propulsive systems and landing legs," said Ed Weiler, associate administrator of NASA's Science Mission Directorate.

The most powerful camera ever sent to the Red Planet, the HiRISE camera aboard the Mars Reconnaissance Orbiter spacecraft, will attempt to image the Phoenix lander from space at about 0600 PDT (1400 GMT) on Monday.

Astrobiology - Learn more in our out-of-this-world special report.

Mars Rovers - Mars is full of surprises; learn more in our continually updated special report.

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