Mars’ Climate Changing
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You think the red planet is lifeless, only famous for its dust storms and has stopped evolving since its rivers and lakes have dried up almost three and a half billion years ago. No. Images taken recently by NASA’s Mars Odyssey spacecraft turn this monotonous view of Mars upside down. The images reveal that Mars’ climate has been changing ever since the loss of its surface water. Using a special imaging technique called Thermal Emission Imaging System (THEMIS), the spacecraft captured the minute geological details of the red planet. The research team in charge of THEMIS reports their findings in an issue of Science. “THEMIS is creating new data that is going to revolutionize our mapping of the planet and our idea of the planet’s geology,” said Philip Christensen, lead author and THEMIS principal investigator from the Geological Sciences at Arizona State University.
Using infrared camera, THEMIS unveiled many secrets of the Martian surface. The imaging system detected layers in the Martian surface that bear telltale signs of the past environmental changes. “With a visible light camera, I can take a picture of a lava flow,” said Christensen. “But, with the existing high resolution camera, the smallest thing we can see is the size of a bus.” In order to do geology, we need to have more detail, he added.
The camera on Mars Global Surveyor reveals exquisite details of the layers in the Martian surface. “But, it does not tell anything about composition – is it a layer of boulders with a layer of sand on top?” said Christensen. “I have no way of knowing.” The THEMIS temperature data, on the other hand, decipher 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 frequent stroll on a sandy beach knows that fine-grained sand heats up more rapidly at the surface than solid stone, which transmits more heat inward. The fine-grained sand also cools off very rapidly at night, when 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 layer, each layer faced different environmental condition. “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 for year after year for billion years.” Christensen and his colleagues have found kilometer-wide stretches of bare bedrock, which are peculiar given the Mars’ well-known dustiness. Such large areas of exposed rock indicate that strong environmental forces are currently at work.
The research team has also found accumulations of loose rock on Martian hillsides, indicating that recent processes of weathering 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 – it is an active place.” It also underscores the fact that water is not the only factor contributing to the observed geological feature of the planet. The team has identified specific mineral deposits that have affected the planet’s geological feature. A mineral known as Olivine has been found near the bottom of a four and a half kilometer canyon known as Ganges Chasma. Olivine, Christensen says, is significant because it decomposes rapidly in the presence of water.
This offers an interesting perspective of water on Mars. “If the canyon harboured water, the olivine would have disappeared,” he said. “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 has been exposed for hundreds of millions of years.
The Odyssey has already given an exciting picture of the planet. “We have discovered that Mars has a really dynamic geologic history,” Christensen said. “It has far more ice and water than we thought – we are seeing snow and gullies, layers – and there are processes involving volcanoes, impact craters and wind.” The planet is so fascinating and intriguing that it will keep scientists busy for the next 20 years trying to understand the processes that have sculpted its landscape.
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