When NASA's Phoenix Mars Lander sets down in the Martian arctic on Sunday, it will open a new, icy frontier for scientists back on Earth.

Phoenix, a stationary lander set to make a planned May 25 descent to the Martian surface, is going to where no probe has gone before - the northern plains of Vastitas Borealis on Mars.

"Ten years ago, you wouldn't have chosen this spot at all because it looks just like every other part of Mars," said Phoenix principal investigator Peter Smith of the University of Arizona. "A lot of the features aren't even named up there."

But it's the promise of what lies beneath the frozen surface features, signs of untouched Martian water ice first spotted by orbiters in 2002, which spurred NASA engineers and researchers to launch the $420 million Phoenix last August.

Wielding its robotic arm like a backhoe, Phoenix is designed to dig down in to the Martian soil to collect water ice samples. It will feed them into small onboard ovens and beakers to determine if its landing site may have once been habitable for microbial life.