Hot Camera Points to Mars
Viewing Mars from orbit has given scientists a view of the red planet that is so detailed, they can resolve objects the size of a bus. What they’ve found so far makes Mars look quite dramatic–not the dusty, uniform place where the landscape never changes.
The first overview analysis of a year’s worth of high-resolution infrared data gathered by the Thermal Emission Imaging System (THEMIS) on NASA’s Mars Odyssey spacecraft is opening Mars to a new kind of detailed geological analysis and revealing a dynamic planet that has experienced dramatic environmental change.
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"THEMIS is creating a set of data that is going to revolutionize our mapping of the planet and our idea of the planet’s geology," said lead author and THEMIS Principal Investigator Philip Christensen, Korrick Professor of Geological Sciences at Arizona State University. "It will keep Mars scientists busy for the next 20 years trying to understand the processes that have produced this landscape."
THEMIS is providing planetary geologists with detailed temperature and infrared radiation images of the martian surface. The images reveal geological details that were impossible to detect even with the high-resolution Mars Orbital Camera on NASA’s Mars Global Surveyor and that have 300 times higher resolution than MGS’s Thermal Emission Spectrometer. Among the significant findings noted in the report is the detection of layers in the martian surface that indicate major changes in past environmental conditions.
"With a visible light camera, I can take a picture of a lava flow, but even with the highest resolution cameras that we have today the smallest thing we can see is the size of a bus and in order to do geology I need to have more detail," said Christensen.
"The camera on Mars Global Surveyor 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 temperature data, I can actually get an idea because the layers vary – and each layer has remarkably different physical properties."
Bedrock vs. Rocky Beds
Daytime and nighttime temperature data can allow scientists to distinguish between solid rock and a variety of loose materials, from boulders to sand and dust. As any beach-goer knows, fine-grained sand heats up more rapidly at the surface than solid stone (which transmits more heat inward) but it also cools off more rapidly at night, when solid materials retain heat.
|Frozen water and carbon dioxide over martian poles.
"We have seen layers, each with dramatically different physical properties, in places like Terra Meridiani," Christensen said. "Why do the physical properties in the different layers change? They change because the environment in which those rocks were deposited changed.
"It’s very difficult to say exactly what happened in any particular place, but what we’ve found is that in many places on Mars it hasn’t just been the same old thing happening for year after year for billions of years. These data have been so remarkable and so different from all of our previous experience that it has taken time to sift through the images and figure out what we’re seeing."
Among the details that have stood out so far are kilometer-wide stretches of bare bedrock that Christensen notes were unexpected, given the Mars’ known dustiness. 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," Christensen pointed out. "This shows a dynamic Mars – it’s an active place."
However, despite Odyssey’s past findings of significant martian ice deposits, there are also indications that, in many places on the planet, water may not be one of the active causes behind the observed geological features. Earlier this year, Christensen proposed gullies are carved by water melting and flowing beneath snow packs, where it is sheltered from rapid evaporation in the planet’s thin atmosphere. There have been other scientific theories offered to explain gully formation on Mars, including seeps of ground water, pressurized flows of ground water (or carbon dioxide), and mudflows caused by collapsing permafrost deposits, but no explanation to date has been universally accepted. The scientific community has remained puzzled, yet has been eagerly pursuing various possibilities.
The Olivine Mystery
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Analyzing the spectra from the ten different bands of infrared light the instrument can detect, the THEMIS team has begun to identify specific mineral deposits, including a significant layer of the mineral olivine near the bottom of a four-and-a-half kilometer deep canyon known as Ganges Chasma. Olivine, Christensen notes, is significant because it decomposes rapidly in the presence of water.
"This gives us an interesting perspective of water on Mars," he said. "There can’t have been much water – ever — in this place. If there was groundwater present when it was deep within the surface, the olivine would have disappeared. And since the canyon has opened up, if there had ever been water at the surface it would be gone too. 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."
Overall, Christensen notes that the emerging diversity and complexity of the planet point to the likelihood of future surprises and keep enlarging the possibilities for discovery on Mars.
"With Odyssey, we are looking at Mars in its entirety, in context. It’s remarkable how much this has already changed our view of the complexity and richness of the planet. 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."
Although Mars is a small planet – its radius is just a little over half the Earth’s – its exposed dusty surface is equivalent to our terrestrial landmass. The martian landscape offers some of the most dramatic vistas found anywhere. Mars boasts a volcano three times higher than Mt. Everest. Called Olympus Mons, it rises 26 kilometers (nearly 16 miles) above the surrounding plains and is the solar system’s highest volcano.
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Additionally a single canyon-Valles Marineris- runs over a fifth of Mar’s equatorial circumference: nine times longer than the Grand Canyon and five times deeper. This feature is such a vast planetary split, that the entire length of the Grand Canyon could fit in just the width of Valles Marineris.
Beyond what Mars has done to itself–its canyons and volcanoes — the rest of the solar system has contributed one of the best ways to determine the age of such features: impact craters. Newer surfaces have fewer craters. The largest crater, called the Hellas Basin, is enormous: 1400 miles (2300 km) wide and nearly 5 miles (9 km) deep. The size of this crater alone would engulf the geographic distance of a big chunk of the United States, from New York City to Houston.
As robotic explorers prepare for their three planned landings early next year, the surface of Mars appears anything but uniform and dull. From the relatively smooth Northern Hemisphere to its rugged southern counterpart, Mars offers enough intriguing topography to match its prominence in scientific thinking about the search for life elsewhere.
In addition to Christensen, the authors on the paper include Joshua L. Bandfield, James F. Bell, Noel Gorelick, Victoria E. Hamilton, Anton Ivanov, Bruce M. Jakosky, Hugh H. Kieffer, Melissa D. Lane, Michael C. Malin, Timothy McConnochie, Alfred S. McEwen, Harry Y. McSween, Greg L. Mehall, Jeffery E. Moersch, Kenneth H Nealson, James W. Rice, Mark I. Richardson, Steven W. Ruff, Michael D. Smith, Timothy N. Titus, and Michael B Wyatt.
Related Web Pages
Evidence for Snow on Mars – and Perhaps an Abode for Life?
Mars Odyssey web site (with new images)
Mars by Stories
Impact Crater Landing Sites for the 2003 Mars Exploration Rovers
Mars Exploration Rover Homepage
2003 Mars Exploration Rover Mission