But that knowledge will have to be vastly improved if a manned mission to Mars -- as NASA plans -- is to have any chance of success.
The Mars Reconnaissance Orbiter aims to do just that. The 2-ton spacecraft is due to arrive at its destination next March. Using the friction of the Martian atmosphere as a brake, it will then slowly dip into a low orbit some 300 kilometers above the surface.
From that position, scientists hope that the spacecraft, which is equipped with high-resolution cameras and radar equipment, will be able to map most of the Martian surface to an unprecedented degree.
The head of NASA’s Mars exploration program, Doug McCuistion spoke proudly of the orbiter’s capabilities at a news conference earlier this week.
“[The] Mars Reconnaissance Orbiter is a weather satellite, a geological explorer, a communications satellite, and an expedition pathfinder hunting for landing sites for the future -- both robotic and human," McCuistion said. "It's got a critical strategic role in the Mars exploration program's 'follow the water' strategy.”
Peter Bond, of Britain’s Royal Astronomical Society, explained that to this point, knowledge of the Martian surface remains very general. Previous orbiting satellites have provided comparatively low-resolution photos. And the spectacular, high-resolution pictures shot by the United States' unmanned "Spirit" and "Opportunity" vehicles cover only a tiny portion of the planet. The Mars Reconnaissance Orbiter should expand our view enormously.
"For example, one of the cameras will be able to pick up an object the size of a desk on the surface. So it will be able to look for small rocks, layers in the rocks -- that sort of thing," Bond said. "Also, another camera will be able to look at the surface in large areas in high resolution because most of the high-resolution images we have at the moment cover only a small percent of the surface of Mars. So that's really like looking at one state in America or one small country in Europe. And the rest of it we haven't really seen in high detail."
As McCuistion noted, mapping potential water reserves on Mars will be a key part of the mission. The recent discovery that the planet appears to have large frozen lakes just beneath its rocky surface has greatly encouraged scientists. Those reserves could eventually be used, some believe, by astronauts sent to the red planet.
"There are other instruments which will be looking for water or signs of water in much more detail, again, than we've done before," Bond said. "And there is also a ground-penetrating radar which will be able to look beneath the surface and look for layers beneath the surface -- possibly even layers which have water in them."
Having an accurate and detailed picture of the entire planet is crucial to laying the groundwork for a manned mission, Bond said.
"Eventually, of course, the NASA plan -- and the Europeans and the Japanese are hoping to be involved in this as well -- is to send humans to Mars," Bond said. "And obviously, if you're going to send people to risk their lives over that huge distance, you need to have safe landing sites already planned. Although that's a long, long way ahead -- maybe 25-30 years perhaps -- they're still thinking they need to start mapping the surface at high resolution now. And that will give them an idea of the potentially good safe landing sites for humans one day."
If the Mars Reconnaissance Orbiter is successful, NASA plans to send two further probes to the planet’s surface for further research -- the Phoenix Mission in 2008 and the Mars Science Laboratory in 2010.