In a departure from previous missions -- which have seen robotic vehicles explore the planet's hills and craters -- NASA's Phoenix Mars Lander will instead dig into Martian soil for conditions favorable to past or present life.

US scientists want Phoenix to try and determine whether frozen water near the planet's surface might periodically melt enough to sustain a viable environment for microbes.

"Phoenix will complement our strategic exploration of Mars by being our first attempt to actually touch and analyze Martian water -- water in the form of buried ice," said Doug McCuistion, director of the Mars Exploration Program.

Phoenix will blast off from Florida sometime in August, beginning a journey that will end several million miles and around nine months later with a risky descent and landing.

Once safely in position on the Martian surface, Phoenix will deploy a set of advanced research tools never before used on the planet.

The solar-powered craft is equipped with a 2.3 meter (7.5 foot) robotic arm that will go vertically into the soil, aiming to strike the icy crust that is believed to lie within a few inches of the surface.

Peter Smith, Phoenix's principal investigator at the University of Arizona, Tucson, said the craft would be able to study the history of the ice and analyze how liquid water has modified the chemistry of the soil.

"In addition, our instruments can assess whether this polar environment is a habitable zone for primitive microbes," Smith said.

The Phoenix's robotic arm is capable of lifting samples to two instruments on its deck. One instrument will use a heater to check for water and carbon-based chemicals considered essential building blocks for life, while the other will analyze the soil chemistry.

The lander also boasts an onboard meteorology station which will assess water and dust levels in the atmosphere as well as monitor weather throughout the three-month-long mission.

First, however, Phoenix must touch down in one piece.

"Landing safely on Mars is difficult no matter what method you use," said Barry Goldstein, the project manager for Phoenix at NASA's Jet Propulsion Laboratory in Pasadena, California.

"Our team has been testing the system relentlessly since 2003 to identify and address whatever vulnerabilities may exist."

As with previous Mars missions, the Phoenix will deploy a heat shield to slow its high-speed entry, before opening a supersonic parachute that will slash its speed to about 217 kilometers (135 miles) per hour.

The lander then separates from the parachute and fires pulsed descent rocket engines to slow to about 9 kilometers per hour (5.5 miles per hour) before landing on its three legs.

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