By Dr David Whitehouse
BBC News Online science editor
A new view of the geology of Mars is emerging from data gathered by the Mars Odyssey (MO) spacecraft which has been observing the Red Planet for a year.
Ganges Chasm in geological detail
The probe is providing a new understanding about the composition of Mars' surface rocks, geological history, radiation levels and potential landing sites for rovers.
"In just one year, Mars Odyssey has fundamentally changed our understanding of the nature of the materials on and below the surface of Mars," says Jeffrey Plaut, Odyssey's project scientist.
The first large-scale geological map of the planet contains many surprises such as the discovery of a layer of olivine-rich rock exposed in the walls of Ganges Chasm.
"Olivine is easily destroyed by liquid water, so its presence in these ancient rocks suggests that this region of Mars has been very dry for a very long time," says Philip Christensen, of Arizona State University, US.
Day and night images
The infrared camera on MO has provided a remarkable new tool for mapping the Martian surface.
"The temperature differences we see in the day and night images have revealed the effects of lava flows, impact craters, wind and possibly water throughout the history of Mars," says Christensen.
Gusev crater: A possible landing site for rovers
Odyssey has also measured radiation levels on Mars, confirming that they are substantially higher than in low-Earth orbit, something that will affect future manned missions to the planet.
"The Martian radiation environment experiment has confirmed expectations that future human explorers of Mars will face significant long-term health risks from space radiation," says Cary Zeitlin of the National Space Biomedical Research Institute, Houston.
"We've also observed solar particle events not seen by near-Earth radiation detectors."
In a new light
The gamma ray spectrometer which last year discovered vast amounts of water-ice trapped beneath the Martian surface, has also mapped the elemental composition of the surface.
"We are seeing Mars in a whole new light - gamma ray 'light' - and that's showing us aspects of the surface composition never seen before," says William Boynton, also of the University of Arizona.
MO has produced new maps of the surface distribution of iron (responsible for the planet's red colour), thorium and silicon.
These are all abundant elements whose presence is essential to understanding the global and regional evolution of the planet.