Nasa's Phoenix will dig for water, life at Martian pole

Jean-Louis Santini

Nasa on Saturday is to launch space probe Phoenix on a nine-month journey to Mars' arctic region, where it will dig through ice for clues to past or present microbial life on the red planet.

The Phoenix Mars Lander is scheduled for blast-off from Cape Canaveral, Florida on August 4, with a first attempt at 9.36am GMT, and a second attempt, should it be needed, at 10.02am GMT.

It was originally scheduled to launch on Friday, but postponed 24 hours after adverse weather on Tuesday prevented fueling of the two-stage Delta II rocket that will propel Phoenix into space.

The space probe's full launch window for its 680-million kilometre, $420-million mission to Mars extends until August 24.

If all goes according to schedule the Phoenix should land on Mars in late May 2008.

Nasa hopes to land the probe on flat ground with few or no rocks at a Martian latitude equivalent to northern Alaska on Earth.

At that site the Phoenix is likely to face temperatures that range from -73C to -33C.

Once it lands safely on the Martian surface, the probe will deploy a set of research tools never before used on the planet.

The solar-powered craft is equipped with a 2,35m robotic arm that will enter vertically into the soil, aiming to strike the icy crust that is believed to lie within a few inches of the surface.

The Phoenix's robotic arm will lift soil samples to two instruments on its deck. One instrument will check for water and carbon-based chemicals, considered essential building blocks for life, while the other will analyse the soil chemistry.

Many scientists see signs of ancient rivers and oceans on the arid and sterile surface of Mars, and believe the planet may once have harboured some forms of life.

In 2002, the Nasa probe Mars Odyssey detected huge quantities of hydrogen on the Martian surface, a likely sign there could be ice at a depth of less than one metre.

Unlike Nasa rovers Spirit and Opportunity, which have been rolling across the Martian landscape since 2004 powered by their solar batteries, the Phoenix will stay in one place on the Martian ground.

And unlike the rovers, which made a bouncy landing on Mars inside huge air bags, the Phoenix is programmed to carry out a soft touchdown.

As with previous missions, the Phoenix will deploy a heat shield to slow its high-speed entry into the Martian atmosphere. It will then open a supersonic parachute that will cut its speed to about 217km/h.

The lander then separates from the parachute and fires pulsed descent rocket engines to slow the craft to about nine kilometres per hour before landing on its three legs.

Fifteen minutes after landing, the probe's solar panels will deploy and power up its instruments.

The Phoenix measures 5,5m by 1,5m and carries 55kg of scientific equipment. - AFP