Professor Iwan Williams of Queen Mary's College in London is a member of the radar team on the European "Mars Express" spacecraft mission that will be searching for water.
"All the evidence so far is that at some time in the past there have been large amounts of water on Mars. We've seen all these dried up riverbeds, etc. And the water that was underground, there is no reason why that should ever have vaporized. So my expectation is, we will find water," Williams said.
Such a discovery could significantly speed up plans to send astronauts to the red planet. Water has already been found frozen in the inhospitable polar regions of Mars. If found elsewhere on the planet, future astronauts could drill wells and obtain water for drinking and growing greenhouse vegetables. A simple electrolysis process can also break water into oxygen and hydrogen, both for breathing and for rocket fuel for the journey back to Earth. That means rockets ferrying astronauts to Mars could be much smaller and cheaper.
Rudolf Schmidt is the European Space Agency's "Mars Express" project manager.
"We have to wait for the radar to deliver the data. But personally I am optimistic that, after having found so much water in the shape of ice on the surface, I think it's likely that there is water under the surface," Schmidt said.
The radar he refers to is the spacecraft's pioneering device known as MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding).
"We expect that the waves penetrate down to four-kilometer depths of the planet. During this penetration, they will be reflected on, for instance, transitions from rocks to ice or rocks to water. And the antenna on the spacecraft detects the echo," Schmidt said.
"Mars Express" has been orbiting the red planet since December 2003. The deployment of the radar's two 20-meter telescopic poles was postponed for a year due to fears they could wrap themselves around the spacecraft.
A few days ago, one of the poles was successfully deployed after engineers fixed a problem with one of its sections not locking into place. The spacecraft was turned so that the sun could warm the stiffened joint.
"We have done it. Since this morning [11 May], the boom is fully deployed. Our first recovery action was to increase the temperature of the stiffened hinge. Overnight, the hinge jumped into final position. So the boom is fine and fully deployed," Schmidt said.
Schmidt says the second 20-meter boom should be deployed in a few weeks. And then the search for water can begin in earnest.
"Both booms deployed means we have an antenna length of 40 meters, and the radar can already be switched on. As soon as the second boom is out, the scientists can start tests, and get first scientific data," Schmidt said.
There is not enough mission time for the spacecraft to look for water on the entire planet. Instead, Williams says, it will focus on several geologically promising regions.
"The 'Mars Express's' lifetime is not sufficient for us to map all of Mars. We can only do certain regions. In those regions, one should be able to map the extent. I would expect to find hopefully very large areas where there is water. I mean tens of kilometers wide," Williams said.
Schmidt says a region known as the Elysium Plains near the planet's equator looks particularly promising. Cameras on "Mars Express" have already discovered what look like sand-covered ice floes. Scientists believe the region may hide a recently frozen sea.