Science2014-06-13 5:02 PM

机遇号的新的结果补充了好奇号的结果 Ancient Aqueous Environments at Endeavor Crater, Mars

论文摘要 

 美国宇航局(NASA)的机遇号探测车是在2004年登陆火星的--当时是好奇号探测车在火星降落之前8年多,来自此次飞行使命的新的数据现在显示,在远古时期造成奋进陨石坑的撞击之前及之后,水曾经冲击过该陨石坑的边缘岩石。然而,据Raymond Arvidson及其同事在本星期所报告的新的机遇号的发现,在奋进陨石坑形成之前,冲刷该区域的水是近乎中性的(略带酸性),而它会比该撞击之后流至那里的水对微生物的生命更为适宜。他们的发现与该探测器在1月25日登陆火星10周年的时间一致,它给来自好奇号探测器的不断增加的研究内容有了新的增添,而好奇号探测器的目的是对火星上的可居住性进行评估。
Arvidson与他的同事解释说,来自火星勘测轨道飞行器的数据表明富含铁与铝的粘土矿物的存在并指引机遇号探测器前往奋进陨石坑的边缘;奋进陨石坑是在37亿多年前形成的。机遇号在那里对Matijevic构造进行了采样,后者是一群富含粘土矿物的细粒、分层的岩石。研究人员分析了这些富含矿物质岩石中的球粒、岩脉及破裂并确定这一Matijevic构造所代表的是机遇号迄今所遇到的最古老的火星岩石--及最早的水活动事件。与位于Matijevic构造顶部的较年轻的岩石不同——那些岩石含有会让甚至是最顽强的嗜极微生物难以生活的超咸、高度酸性水的特征,这些较古老的岩石则与较温和的会对生命或生命起源前化学较为有利的条件相关。综合来看,这些结果提示,在奋进号陨石坑形成之前与之后,具有不同 pH 值的水曾经在这一区域流动。由John Grotzinger撰写的有关本杂志一个特别版面的介绍文章将这一新的发现与好奇号最近的发现进行了结合以对火星的可居住性进行一个深度的概述。

Abstract 

Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe+3-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

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