A British scientist says he is confident that Europe's first solo mission to Mars will find water under the surface of the Red Planet.
By Helen Briggs
BBC News Online science reporter
Professor Iwan Williams says a radar instrument (Marsis) on the Mars Express spacecraft can look deep enough to find water, if it is there.
The spacecraft has a suite of scientific instruments
"There is real reason to believe there's water on Mars underneath the surface and Marsis should detect that," he told BBC News Online. "Everyone is 100% confident that we will find it."
Two US space agency (Nasa) spacecraft orbiting Mars have recently uncovered tantalising clues that water once flowed on Mars and is now hidden under the surface.
The Mars Global Surveyor spacecraft has spotted what look like channels and river valleys carved by running water.
Almost a year ago, the Mars Odyssey spacecraft detected a signal suggesting ice crystals exist at a depth of about a metre.
Once Mars Express is in orbit around Mars, Marsis will beam radio waves towards the planet from a huge antenna.
Some of these should penetrate the crust, probing the composition of the hidden layers of rock and possibly water.
Professor Williams, of the astronomy unit at Queen Mary University of London, says the radar instrument on Mars Express will be able to search much deeper below the surface than ever before - down to about five kilometres.
The professor, who will discuss the matter at the UK/Ireland National Astronomy Meeting in Dublin, is optimistic that the search will be successful.
"If we don't find water it will cause a serious change in what we think about Mars and what it's like," he said.
Mars Express is due for launch from Baikonur Cosmodrome, Kazakhstan, in June 2003.
It will carry six experiments in addition to the Marsis radar. Also on board will be the British-built Beagle 2 spacecraft, which will land on the Red Planet around Christmas 2003 and carry out a search for signs of primitive life - past or present.