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Mars much wetter in the past |
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Written by Derek Kessler on
Sunday, 20 July 2008
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 Studying observations from NASA’s Mars Reconnaissance Orbiter, scientists have discovered evidence that huge swaths of Mars’ southern highlands were extensively altered by water billions of years ago. The orbital images revealed the southern hemisphere to be covered in phyllosilicates, rocks formed only in water, such as clays rich in iron, magnesium, aluminum, mica, and kaolinite. The phyllosilicates were formed between 4.6 billion and 3.8 billion years ago.
Phyllosilicates are formed in atomic layers. Their crystalline structures hold water and hydroxyl (oxygen and hydrogen). Previous scans of Mars made by the ESA’s Mars Express revealed only a few large outcrops of phyllosilicates. With the MRO’s higher resolution instruments, phyllosilicates outcrops have been resolved all over the southern hemisphere, which is dominated by older rocks (the northern hemisphere has undergone extensive volcanism).
The pervasiveness of the phyllosilicates indicates that there is an extensive subsurface layer of water-formed clays and minerals. Many of the outcrops were uncovered from under dust and younger volcanic rocks by craters, surface fractures, and valleys such as the massive Valles Marineris.
Because the phyllosilicates are only present in the older Martian rocks, scientists have determined that around 3.7 to 3.5 billion years ago Mars’ geology was no longer effected on such a large scale by water. Back then, the water was omnipresent throughout Martian geology, just as it is on Earth today. Minerals such as chlorite, which is formed in areas with light water exposure. Others, like mica, are formed in the presence of high temperature water, or kaolinite where water has dissolved out all the iron and magnesium.
Even so, the best observations of the rocks can right now only be made from orbit. The two Mars rovers, Spirit and Opportunity, are both in the northern hemisphere and nowhere near any of the detected outcrops. However, that does not mean that there are not such rocks near the rovers, as just a few micrometers of dust would be enough to obscure the MRO’s orbital readings.
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