Nasa's latest mission to Mars, the Phoenix lander, is due to launch on 3 August and arrive in May 2008. 

The Phoenix mission is the first attempt to actually touch and analyse Martian water in the form of buried ice.

The lander will investigate whether frozen water near the Martian surface might periodically melt sufficiently to sustain a habitable zone for primitive microbes.

Phoenix will carry the most sophisticated set of advanced research tools ever used on Mars, including a robotic arm, camera, surface stereoscopic imager, thermal and evolved gas analyser, microscopy, electrochemistry and conductivity analysers, meteorological station and a Mars descent imager.

Phoenix will land on the Red Planet's northern plains in the area known as Vastitas Borealis where it will claw down into the icy soil.

Scientists will have just three months to complete their tasks before the Martian winter sets in and the solar panels no longer provide enough power to run the instruments.

UK scientists from the University of Bristol and Imperial College London have provided hardware and are involved in the science operations. 

One of the objectives of Phoenix in which they will be involved is monitoring the polar weather and the interaction of the atmosphere with the surface.

"The polar summer atmosphere is not subject to the huge daily temperature swings that are experienced at lower latitudes," said Dr David Catling from the University of Bristol.

"The Northern summer is the time of year when water vapour is driven off ice at Mars' north polar cap and enters the atmosphere.

"In studying the movement and behaviour of water on present-day Mars, we can better understand how it may have behaved previously.

"In the past, Mars experienced big ice ages when water ice extended into the tropics and probably melted in some places, providing possible habitats for life."

Nasa already has two Mars Rovers - Spirit and Opportunity - on the surface of the planet just south of the Martian equator.

However, this month a series of huge Martian dust storms threatened to bring their investigations to a halt because the dust blocks the sunlight which powers the rovers.

Opportunity has been knocked the hardest as 99 per cent of the sunlight reaching the planet surface has been blocked in the region where it is operating, just as it was due to begin a dangerous descent into the vast 60m deep Victoria crater.

The rovers were given a fourth software upgrade in January. Nasa scientists fear that if sunlight is blocked for an extended period of time, the rovers will drain their batteries and become unrecoverable.

Earlier this month Nasa postponed until September its Dawn mission to the asteroid belt because delays to Dawn would have clashed with Phoenix' three-month launch window.