Happy landings: Phoenix eases its way down to the surface.

Credit: NASA

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WASHINGTON DC: After a nine-month journey through space, the U.S. probe Phoenix will land on the arctic surface of Mars on Sunday to dig for ice in a new quest for signs of life on the Red Planet.

NASA's US$420-million (A$438-million) probe will become the first spacecraft to land on the Martian arctic surface and will stay there for a three-month mission.

After travelling 679 million km, Phoenix will enter the top of the Martian atmosphere at around 11:31pm GMT (9:31am Monday, Sydney time), zipping in at 21,000 km/h to begin a perilous descent that will end with a soft landing seven minutes later.

An agonizing 15 minutes

But the U.S. space agency's Jet Propulsion Laboratory (JPL) in Pasadena, California, which controls the mission, will have to wait an agonizing 15 minutes for the radio signal confirming the safe landing to reach Earth.

Like previous Mars landers, Phoenix is equipped with a thermal shield to slow its entry into the atmosphere and will deploy a parachute to slow its speed. The probe will then fire up its thrusters to slow its descent to eight kilometres per hour and land on its three legs on the circumpolar region known as Vastitas Borealis – akin to northern Canada in Earth latitude.

One minute after Phoenix confirms arrival, its radio will go silent for 20 minutes to save its batteries before deploying its two solar antennas. The first images from Phoenix will reach Earth two hours later.

Watch a NASA video here about the probe's entry and descent.

"Putting a spacecraft safely on Mars is hard and risky," said Ed Weiler, associate administrator for NASA's Science Mission Directorate. Since Mars exploration began in the 1970s, more than half, or 55 percent, of probes sent to the Red Planet have failed to reach their destination.

"We do believe that it's a risk worth taking," said Fuk Li, manager of NASA's Mars Exploration program, "because I think that the science the mission will return with will be outstanding and we will open up a new chapter on how we understand Mars to be."

"The Phoenix mission not only studies the northern permafrost region, but takes the next step in Mars exploration by determining whether this region, which may encompass as much as 25 per cent of the Martian surface, is habitable [for future manned missions]," said Peter Smith, Phoenix principal investigator at the University of Arizona, USA.

Arctic life

NASA wants to assess whether the Martian arctic ever had conditions favourable to microbial life. The probe will also help determine if a primitive life form was ever or is still present on Mars.

"The Arctic region is a place where there is a lot of things we are learning about the Earth," said Smith. "One is the climate change for our planet is written into the ices in the Arctic region on the Earth," he said.

The robot's instruments can detect carbon and hydrogen molecules, essential elements of life. With its two solar panels unfurled, Phoenix is five metres wide and one and half metres long. It weighs 350 kg, including 25 kg of scientific instruments.

Phoenix will be the latest ambitious mission to explore Mars. The U.S. Mars Odyssey orbiter detected vast quantities of hydrogen on the planet's surface in 2002, a sign that its polar regions are covered in ice. The roving robots Spirit and Opportunity, which have roamed the Martian surface's equator for three years, have also discovered signs of past water.