Mars lander is 'in good health'

Polygon patterns are similar to those in permafrost regions on Earth

Nasa says its Phoenix spacecraft is in good health after making the first successful landing in the north polar region of Mars.

Images sent back show a flat valley floor with polygonal features that give the ground a "paved" appearance.

These are believed to be a sign of the water-ice that lies just beneath the surface at these high latitudes.

The ice should be within reach of the probe's 2.35m-long robotic arm, which is due to be deployed this week.

The arm can dig through the topsoil to the ice beneath and scoop up samples to return to the lander's deck for analysis.

Phoenix is set to investigate the planet's geological history and search for the chemical building blocks which could support life.

The polygons seen in the latest images have previously been spotted from space and are thought to be caused by expansion and contraction of ice. Similar features can be seen in permafrost regions on Earth.

A Nasa orbiter took this image of Phoenix parachuting to the surface

"We see the lack of rocks that we expected, we see the polygons that we saw from space, we don't see ice on the surface, but we think we will see it beneath the surface. It looks great to me," said Professor Peter Smith, principal investigator for the Phoenix mission.

But Professor Smith also mentioned that the polygons were smaller than expected.

Some scientists think there may be a large-scale polygonal structure to the Martian surface as seen from space. But from the ground, it seems there are polygons within polygons.

This suggests that water-ice could lie very near the surface indeed: the closer it is to the surface, the more fractured it becomes, leading to smaller polygon shapes.

A signal confirming the lander had reached the surface was received at 2353 GMT on 25 May (1953 EDT; 0053 BST on 26 May).

Engineers and scientists at Nasa's Jet Propulsion Laboratory (JPL) in California clapped and cheered when the landing signal came through.

Soft landing

The final seven minutes of the probe's 10-month journey to Mars were regarded as the hardest part of the mission.

The probe had to survive a fiery plunge through the planet's thin atmosphere, slowing from a speed of nearly 21,000km/h (13,000 mph).

It released a parachute, used pulsed thrusters to slow to a fast-walking speed, and then descended the last few metres to the Martian soil to land on three legs.

The Nasa team monitored each stage of the descent and landing process through radio messages relayed to Earth via the Odyssey satellite in orbit around Mars.

Phoenix carries seven science instruments

Nasa found out more about the landing when pictures from the probe reached the Earth.

The first pictures confirmed that the solar arrays needed for the mission's energy supply had unfolded properly, and masts for the stereo camera and weather station had swung into their correct vertical position.

HOW PHOENIX LANDED

Phoenix lander craft jettisons cruise- stage power equipment seven minutes before reaching Mars' atmosphere.

Phoenix approaches Mars' atmosphere at 21,000km/h. The heat shield can withstand temperatures of 1,420C.

About 13km above Mars' surface, Phoenix deploys its parachute and the heat shield is jettisoned.

Radar is activated providing information to the onboard computer, which will calculate final descent.

Lander separates from back shell. Radar and thrusters guide Phoenix to a clear landing.

Over the next three months, Phoenix will analyse the planet’s icy soil to see if life could survive on Mars.

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"Seeing these images after a successful landing reaffirmed the thorough work over the past five years by a great team," said the mission's project manager Barry Goldstein, from JPL.

The spacecraft will begin its three-month science mission in the next few days.

Phoenix is an apt name for the current mission, as it rose from the ashes of two previous failures.

In September 1999, the Mars Climate Orbiter spacecraft crashed into the Red Planet following a navigation error caused when technicians mixed up "English" (imperial) and metric units.

A few months later, another Nasa spacecraft, the Mars Polar Lander (MPL), was lost near the planet's South Pole.

Phoenix uses hardware from an identical twin of MPL, the Mars Surveyor 2001 Lander, which was cancelled following the two consecutive failures.

The probe was launched on 4 August 2007 on a Delta II rocket from Cape Canaveral Air Force Station in Florida.

Phoenix landed further north than previous missions

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