|
|
Mars Is Fascinating
More so because of the processes those have
sculpted its landscape, as Biplab Das finds out
Think Mars is lifeless, that it stopped evolving since its rivers and lakes dried up almost three and a half billion years ago, that it's famous only for its dust storms? Think again? Images taken recently by Nasa's Mars Odyssey spacecraft reveal that the planet's climate has been changing ever since the loss of its surface water. Using a Thermal Emission Imaging System, the spacecraft has captured the minute details, which, according to the 5 June online issue of
Science, "are going to revolutionise our mapping of the planet and our idea of its geology."
Using infrared cameras, Themis, as the system is called, detected layers in the Martian surface that bear telltale signs of past environmental changes. "With a visible light camera, I can take a picture of a lava flow," said Philip Christensen, lead author and Themis principal investigator from the Geological Sciences at Arizona State University. "But with the existing high resolution camera, the smallest thing we can see is the size of a bus."
The camera on the Mars Global Surveyor reveals exquisite details "but it does not tell us anything about composition - is it a layer of boulders with a layer of sand on top? I have no way of knowing," said Christensen. The temperature data, on the other hand, deciphers that each layer has remarkably different physical properties. As every material absorbs and radiates heat differently, daytime and nighttime temperature data can allow scientists to study a variety of loose materials, from boulders to sand and dust.
On earth, anyone who takes a frequent strolls on a sandy beach knows that fine-grained sand heats up more rapidly on the surface than solid stone, which transmits more heat inward. The fine-grained sand also cools off very rapidly at night, where solid materials retain heat. According to Christensen, each layer has dramatically different physical properties in places like Terra
Meridiani.
Why do the physical properties in the different layers change? Because, when one layer was deposited on top of another, each layer faced different environmental conditions. "It is very difficult to say exactly what happened in any particular place," said Christensen. "But, we have found that in many places on Mars it has not just been the same old thing happening year after year for billions of years."
He and his colleagues have found kilometre-wide stretches of bare bedrock, which are peculiar, given Mars' well-known dustiness. Such large areas of exposed rock indicate that strong environmental forces are currently at work. The research team also found accumulations of loose rock on Martian hillsides, indicating recent processes of weathering that are still shaping the red planet. "If those rocks had been made a billion years ago, they would be covered with dust," Christensen pointed out. "This shows a dynamic Mars."
Water is not the only factor that contributes to the observed geological feature of the planet. The team has identified specific mineral deposits that have affected the planet's geological features. A mineral known as Olivine has been found near the bottom of a 4.5 km canyon known as Ganges Chasm. Olivine, Christensen said, is significant because it decomposes rapidly in the presence of water. This offered an interesting perspective. "If the canyon harboured water, the olivine would have disappeared," he said. "Since the canyon has opened up, if there has ever been water at the surface it would be gone too."
"We've discovered that Mars has a really dynamic geologic history. It has far more ice and water than we thought and there are processes involving volcanoes, impact craters and wind." The planet, he said, was so fascinating and intriguing it would keep scientists busy for the next 20 years trying to understand the processes that have sculpted its landscape.
|
|
