Next US Mars probe set for launch
Nasa's latest Mars mission is set to be launched on Wednesday.
The Mars Reconaissance Orbiter (MRO) will search the planet for promising landing sites for future robotic missions, in the US quest to eventually send astronauts to Mars.
The spacecraft could identify suitable habitats for life on the Red Planet.
A rocket carrying the probe is due to blast-off from Cape Canaveral at 7.54am (11.54 GMT).
Water search
The MRO is the biggest spacecraft to be sent to Mars, carrying some of the most sophisticated instruments ever.
"MRO is the next step in our ambitious exploration of Mars," said Douglas McCuistion, director of Nasa's Mars exploration programme.
MRO Cost: $500m Weight: 2,180kg Payload: Three cameras and instruments to analyse the atmosphere of Mars, monitor the Martian weather, study minerals and search for sub-surface water
"We expect to use this spacecraft's eyes in the sky in coming years as our primary tools to identify and evaluate the best places for future missions to land."
The spacecraft will arrive at Mars in March 2006. It will study the composition and structure of Mars and serve as a powerful communications relay for future missions to the surface.
One of its scientific objectives is to explore whether Mars could once have supported microbial life. Its cameras and spectrometers will scour the surface for features related to water, without which life cannot survive. Meanwhile, a radar sounder will look for liquid water reservoirs that may exist beneath the surface of Mars.
Beagle clues
British scientists hope it will also discover what happened to the lost Mars probe, Beagle 2.
Professor Colin Pillinger, from the Open University, who led the Beagle 2 mission, said: "If we could just see some trace of it on the surface then at least we could see how far it got - the not knowing is the worst bit.
"It will be a very difficult thing to do, but this is our best chance of finding out what happened and we will be watching the progress of the mission with great interest and anticipation."
The MRO will join two US orbiters - the Mars Global Surveyor and Mars Odyssey - and one European orbiter, Mars Express, at the Red Planet.
Two US robotic rovers, Spirit and Opportunity, have been on the Martian surface for the past 18 months, investigating the geology of Mars.
Nasa is planning two further Mars mission this decade: the Phoenix module, set for launch in 2007, and a Mars Science Laboratory in 2009.