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TOPIC: Mars - more water

Blobrana

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Posts: 131433

Date: May 28 19:50 2005

RE: Syrtis Major Olivine	Permalink

Olivine (Mg,Fe)2SiO4 is a greenish-coloured silicate mineral common in many mafic igneous rocks (dark-coloured with significant iron and magnesium content). The Nili Fossae region is a fractured and cratered terrain thought to be >3.5 billion years old (Noachian age). It is northeast of Syrtis Major--a broad, very low shield volcano with two summit calderas whose lava flows form a plateau more than 1000 kilometres across. Syrtis Major is thought to be about 3 billion years old (late Hesperian age). Its shape and surface features resemble Hawaiian shield volcanoes and suggest a mafic composition consistent with a basaltic rock type. Its calderas are thought to be located on extensions of ring fractures associated with the Isidis impact crater basin (located to the northeast). The current hypothesis is that the fractures, faults, and grabens (valleys between faults) in Nili Fossae are also related to the formation of the Isidis impact basin. Syrtis Major The presumed age of ~3.6 billion years for the Nili Fossae region, places an upper limit to when the olivine was exposed at the surface. Because olivine weathers rapidly to clays and iron oxides, this implies that no water has flowed there since then. Alternatively, the olivine may have been uncovered more recently, in the past few thousand years or so, and the current cold and dry conditions have slowed or limited chemical weathering. What's needed is a better constraint on how long olivine can exist. __________________

Anonymous

Date: May 28 19:12 2005

Mars - more water	Permalink

By using new, high spatial resolution infrared data from NASA's Mars Odyssey spacecraft, Victoria Hamilton from the University of Hawaii at Manoa and Philip Christensen from Arizona State University have concluded that a region on the surface of Mars known to contain olivine-rich rocks is actually 4 times larger than previously estimated. The bedrock in question is adjacent to Syrtis Major, one of Mars’ largest volcanoes. This region is of interest to scientists because it lies in a relatively old region on Mars, and yet contains significant amounts of olivine, a mineral that can weather rapidly in the presence of water. While Mars today is a dry and cold world, river channels and other water-carved features suggest it may have had a more hospitable past. Since water is a necessary ingredient for life, proof that the substance either existed on Mars or never did would answer one of humanity's enduring questions about the planet. Victoria Hamilton concluded from high-resolution infrared data obtained by the Mars Odyssey spacecraft that larger than earlier believed amounts of olivine sit in a volcanic rock on Mars. Since olivine weathers and rapidly turns into other minerals in the presence of water, the finding of the large deposits may mean that this area of Mars never had much water. The other hypothesis is that the area had water, but the water carried the minerals made from its interaction with olivine away when it washed through, leaving no trace of water behind. A green mineral sometimes used in jewellery, olivine is found in volcanic regions on both Earth and Mars. The Mars bedrock rich with olivine was previously believed to be as large as 19 311 square kilometres but turned out to be almost four times bigger at about 72 417 kilometres. "It's like you've been standing on Kilauea but you've suddenly discovered four more volcanoes. There's so much more than we realized." - Victoria Hamilton. On Earth, olivine can coexist with water because volcanic activity that produced it has taken place more recently than on Mars, leaving less time for it to be weathered or washed away. link: __________________

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