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Scientific Reports:火星上有有机物吗?

摘要 : 关于火星土壤的火星着陆器实验所检测到的氯甲烷排放是否表明火星表面上存在有机物一直是一个有争议的问题,这个问题在本期Scientific Reports上得到了进一步的探讨。

关于火星土壤的火星着陆器实验所检测到的氯甲烷排放是否表明火星表面上存在有机物一直是一个有争议的问题,这个问题在本期Scientific Reports上得到了进一步的探讨。在一个陨石样本上重现的火星着陆器实验显示,氯甲烷来自该陨石中的有机物。这些结果表明,在火星上所观测到的氯甲烷排放可能来自火星表面上陨石碎片中的有机物。

氯甲烷在两次不同的火星探测任务中都被检测到,但一些研究对这种化学物质是土壤内有机物的热反应的一种产物还是地球上的一种污染物提出了质疑。Frank Keppler及同事提出,前者是可能的,因为一个相似的过程(涉及氯存在情况下的有机物)也发生在地球上。他们显示,氯甲烷以这种方式从1969年掉到澳大利亚的Murchison陨石中所含的物质生成了。

对来自Murchison陨石样本的氯甲烷所做分析显示了一个截然不同的同位素特征(一个独特的化学“指纹”),该同位素特征表明它是从来自地球外的有机物形成的。因此,作者提出,对在火星上检测到的氯甲烷进行同位素分析,有可能确定其来源是来自火星本身的有机物、是被陨石沉积的、还是由从地球上发射的着陆器的污染造成的。

原文标题:Chloromethane release from carbonaceous meteorite affords new insight into Mars lander findings

原文摘要:Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars. Here we demonstrate CH3Cl release (up to 8 μg/g) during low temperature (150–400°C) pyrolysis of the carbonaceous chondrite Murchison with chloride or perchlorate as chlorine source and confirm unequivocally by stable isotope analysis the extraterrestrial origin of the methyl group (δ2H +800 to +1100‰, δ13C −19.2 to +10‰,). In the terrestrial environment CH3Cl released during pyrolysis of organic matter derives from the methoxyl pool. The methoxyl pool in Murchison is consistent both in magnitude (0.044%) and isotope signature (δ2H +1054 ± 626‰, δ13C +43.2 ± 38.8‰,) with that of the CH3Cl released on pyrolysis. Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil. However we cannot discount emissions arising additionally from organic matter of indigenous origin. The stable isotope signatures of CH3Cl detected on Mars could potentially be utilized to determine its origin by distinguishing between terrestrial contamination, meteoritic infall and indigenous Martian sources.

原文地址:http://www.nature.com/srep/2014/141113/srep07010/full/srep07010.html

来源: Scientific Reports 浏览次数:88

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