Scientists found in 2002 that Mars's polar regions have vast reservoirs of water frozen beneath a shallow layer of soil. Phoenix was launched on August 4 last year, with a mission to sample the water and determine if the right ingredients for life are present.

NASA attempted a landing on Mars' south pole in 1999, but a problem during the final minutes of descent ended the mission.

The US space agency cancelled its next Mars lander but successfully dispatched two rovers, Spirit and Opportunity, to the planet's equatorial region to search for signs of past surface water.

Phoenix was created out of spare parts from the failed Polar Lander mission and the mothballed probe.

"We haven't landed successfully on legs and propulsive rockets in 32 years," said NASA's space sciences chief Ed Weiler.

"When we send humans there, women and men, they're going to be landing on rockets and legs, so it's important to show that we still know how to do this."