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Analysis of a meteorite from the planet Mars may have laid to rest the possibility of finding life on the Red Planet. A comprehensive imaging study including confocal micro Raman spectroscopy has helped US researchers uncover the origin of organic molecules found in the meteorite and show that these carbon-containing compounds were produced by non-living processes. Andrew Steele and colleagues at The Geophysical Laboratory, Carnegie Institution of Washington, used micro Raman together with scanning electron microscopy (SEM), and three-dimensional extended focal imaging light microscopy to analyse globules of carbonate salts found throughout the depth of the Martian meteorite known as Allan Hills 84001. As the name suggests, organic compounds form the building blocks of life. However, it has been known since the work of Friedrich Woehler and others that just because a compound is composed of carbon, hydrogen, and sometimes other elements including nitrogen and oxygen does not imply that it came from a living thing. There is no vital spark involved in the conversion of the inorganic salt ammonium cyanate into the "organic" compound urea, after all. The Carnegie analysis of ALH 84001 shows that the organic matter present was formed early in Martian prehistory. They compared their results with data collected on related rocks found in Svalbard, Norway, which were formed by volcanic activity in the freezing Arctic climate of 1 million years ago, conditions thought to resemble the surface of the young Mars. Previously, scientists had speculated that these molecules may have been the molecular fossil remnants of ancient Martian microbes. "Organic material occurs within tiny spheres of carbonate minerals in both the Martian and Earth rocks," explains lead author Steele, "We found that the organic material is closely associated with the iron oxide mineral magnetite, which is the key to understanding how these compounds formed." Steele explains that magnetite could have acted as a catalyst for the formation of organic molecules in the Svalbard rock samples from fluids rich in carbon dioxide and water spurting from the volcanoes under freezing conditions. In such conditions no life could exist, so the association of carbonate, magnetite and organic material in the Martian meteorite ALH 84001 provides rather compelling evidence that the organic material had a rather more mundane origin than Martian life forms. Steele's is the first study to show that chemistry on the ancient Martian surface was at one time capable of forming organic compounds. The picture of organic origins is a little more complicated, however. The researchers suggest that two different events may have given rise to the precise composition of the ALH 84001 meteorite. The first would have been similar to the process that formed the Svalbard rock samples - flash cooling of fluids. The second event may have involved formation of organic material from carbonate minerals during impact ejection of ALH 84001 from Mars. "The results of this study show that volcanic activity in a freezing climate can produce organic compounds," adds team member Hans Amundsen of the Earth and Planetary Exploration Services, "This implies that building blocks of life can form on cold rocky planets throughout the Universe." The Carnegie results will provide new inspiration for the Mars Science Laboratory mission in 2009. Steele, who is a member of the Sample Analysis on Mars (SAM) instrument team onboard MSL, adds that, "We now know that Mars can produce organic compounds. Part of the mission's goal is to identify organic compounds, their sources, and to detect molecules relevant to life. We know that they are there. We just have to find them." Presumably, knowing that certain types of organic molecule on Mars may have a non-living origin will help exclude those from any search for actual Martian microbes. So, there may still be some hope of finding ancient life on Mars. Singer-songwriter David Bowie will be pleased. Related links: The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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Steele, eyeing meteorites for signs of organics ALH suggests inorganic origins for Martian organic molecules |
