Washington - After a day's delay because of a radio glitch, NASA Wednesday restored communication with its newest lander, Phoenix and sent instructions for it to start unfolding its robotic arm.

The ground team got around the glitch by using a different satellite in orbit around Mars as its intermediary with the tiny landing craft, NASA officials said.

"This is a contingency that we've always planned for," Barry Goldstein, Phoenix project manager at NASA's Jet Propulsion Laboratory (JPL), said in telecast remarks to reporters. "As it stands, we're in fine shape."

Phoenix is looking for signs of life on Mars by sampling the icy terrain at Mars' north pole, which has never been explored. The question is whether frozen water near the Martian surface might periodically melt enough to sustain a livable environment for microbes.

For most of Tuesday, the Mars Reconnaissance Orbiter refused to relay instructions from Earth to Phoenix, which landed perfectly on the north pole of Mars on Sunday.

So NASA scientists rerouted communications through the older orbiter, Odyssey. Both orbiters had been forseen for use during the mission, depending on which has a better window of communication, the space news website space. com reported.

Goldstein said digging would probably not start before early next week. The robotic arm must be unfolded carefully and according to a step-by-step process.

But NASA was still celebrating Sunday's successful landing - a risky milestone, given the failure rate of at least 50 per cent of Mars missions in the past decades.

The mission is the first in a series of journeys to further explore the availability and chemical make-up of water on Mars, with a view to understanding "the eventual habitability of the northern plains," NASA said last year.

In the 420-million-dollar mission, Phoenix's robot arm will use a scoop shovel to dig as far as one metre into the mixture of ice, rock and dust at its landing place.

Earth scientists have already started nicknaming the landscape around Phoenix, calling the nearby high ground "Humpty Dumpty," a low trough "Sleepy Hollow" and some of the rocks it will have to dodge "King's Men" and "Headless," the journal Nature reported online.

The shovel will dump the material into Phoenix's compact laboratory, where it will be heated and studied for gasses and microbes.

The first evidence of water on Mars was found by the Odyssey in 2002.

Phoenix is to make use of the calm three-month northern Martian summer to carry out its work. Sand storms during the rest of the year would interfere with the solar collectors, just as they have interfered with the hard-working rovers Spirit and Opportunity, which have nevertheless outlived their initial 90-day life expectancy by nearly four years.

In addition, Phoenix will shoot laser beams into the Martian atmosphere to study cloud structure and other elements. After the onset of the Martian winter, the probe will continue to work as a weather station.

Phoenix travelled the 680 million kilometres to Mars over the past ten months. After landing, it ran on batteries until its pair of solar arrays spread open as planned about two hours after touchdown. (dpa)