What lies beneath: The solar-powered craft is equipped with a 2.35-metre robotic arm that will enter vertically into the soil, aiming to strike the icy crust that is believed to lie within a few centimetres of the surface.

Credit: NASA

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SYDNEY: A space probe sent to Mars to dig for signs of life is nearing the end of its nine-month voyage and should touch down on schedule, says NASA.

The Phoenix Mars Lander, which blasted off from Cape Canaveral, Florida, last August, is on course to reach the planet on 25 May, where it will attempt a hazardous descent to the Martian surface.

Phoenix will enter the top of the Martian atmosphere at almost 21,000 km/h. In just seven minutes, the spacecraft must complete a challenging sequence of events to slow to about 8 km/h before its three legs reach the ground.

Risky sequence of events

"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 at the U.S. space agency's headquarters in Washington DC. "Internationally, fewer than half the attempts have succeeded."

NASA has used high-resolution images from a camera on NASA's Mars Reconnaissance Orbiter to help select a landing site for Phoenix.

Phoenix uses hardware from a spacecraft built for a 2001 launch that was cancelled in response to the loss of a similar Mars spacecraft during a 1999 landing attempt. Contact with NASA's Mars Polar Lander was loss before it entered the planet's atmosphere. Another lander, the European Space Agency's Beagle 2, disappeared during descent in 2003.

Researchers who proposed the Phoenix mission in 2002 saw the unused spacecraft from the canned 2001 mission as a resource for pursuing a new science opportunity.

The lander's assignment is to dig through the Martian soil and ice in the Arctic region and use its on-board scientific instruments to analyse the samples it retrieves.

Mission impossible

Phoenix is likely to face Martian temperatures that range from -73 to -33 ºC. Once it lands, the probe will deploy a set of research tools never before used on the planet.

The solar-powered craft is equipped with a 2.35-metre robotic arm that will enter vertically into the soil, aiming to strike the icy crust that is believed to lie within a few centimetres of the surface.

The arm will lift soil samples to two instruments on the deck of Phoenix. One instrument will check for water and carbon-based chemicals – considered essential building blocks for life – while the other will analyse the soil chemistry.

Many scientists see signs of ancient rivers and oceans on the arid and sterile surface of Mars, and believe the planet may once have harboured some forms of life.