New observations of Mars obtained in unprecedented geological detail show the planet to have experienced dramatic change in the past - and these changes continue to this day.
This conclusion comes from studying images sent back by the Themis (Thermal Emission Imaging System) instrument on board Mars Odyssey, the US probe in orbit around the Red Planet.
"Themis is creating a set of data that is going to revolutionise our mapping of the planet and our idea of the planet's geology," said Themis Principal Investigator Philip Christensen, of Arizona State University.
"It will keep Mars scientists busy for the next 20 years trying to understand the processes that have produced this landscape."
Data interpretation
"With Odyssey, we are looking at Mars in its entirety, and in context. It's remarkable how much this has already changed our view of the complexity and richness of the planet," he added.
"We discovered that it has a really dynamic geologic history.
"It has far more ice and water than we thought - we're seeing snow and gullies, layers - and there are also processes involving volcanoes, impact craters and wind. It's a fascinating place," he adds.
"The camera on Mars Global Surveyor, the other spacecraft currently observing Mars, takes exquisite images that show layers, but it doesn't tell me anything about composition - is it a layer of boulders with a layer of sand on top? I have no way of knowing."
"With the Themis data, I can actually get an idea because each layer has remarkably different physical properties."
Changing face
Themis can provide day and night temperature data that allows scientists to distinguish between solid rock and a variety of loose materials, from boulders to sand and dust.
Among the details that have stood out so far are kilometre-wide stretches of bare bedrock that Christensen said were unexpected.
Large areas of exposed rock indicate that strong environmental forces are currently at work, "scouring" from the surface any past sediment as well as any new material that might be falling from the atmosphere.
Also unexpected is the finding that accumulations of loose rock are common on Martian hillsides, indicating recent processes of weathering continuing to affect the planet.
"If those rocks had been made a billion years ago, they'd be covered with dust," said Christensen. "This shows a dynamic Mars - it's an active place."
Dry land
But despite Odyssey's past findings of significant ice deposits, there are indications that in some places water may not be one of the active causes behind geological features.
One series of observations shows a layer of the mineral olivine near the bottom of a four-and-a-half kilometre deep canyon known as Ganges Chasma.
The presence of olivine is significant because it decomposes rapidly in the presence of water.
"This gives us an interesting perspective of water on Mars," said Christiansen.
"There can't have been much water in this place. If there was groundwater present when it was deep within the surface, the olivine would have disappeared.
"This is a very dry place, because it's been exposed for hundreds of millions of years. We know that some places on Mars have water, but here we see that some really don't."
The Themis research is reported in the journal Science.
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