Fe Isotopic Composition of Martian Meteorites

Introduction The scientific community has actively debated for quite some time the possibility that conditions were once favorable for life to originate and evolve on Mars. However, as we know it, for life to survive, the presence of liquid water is essential. The present day climate on Mars is inhospitable for sustaining any life form. However, recent data from twin rovers, Spirit and Opportunity, and Mars Express spacecraft have strengthened previous interpretations and suggestions that Mars was once a warmer and wetter place [e.g., 1]. Until we have a returned sample mission from Mars, one of the ways to look for past evidence of aqueous activity on Mars is through mineral, chemical and isotopic studies of primary and secondary minerals in Martian meteorites. The focus of this research is on understanding the action and effects of water on Mars by using fractionation of iron isotopes (which can be significant during low temperature aqueous processes) to trace the alteration of primary to secondary minerals by water on Mars. Another key aspect of the project is to first establish a baseline Fe-isotope fractionation pattern in the case of high-temperature igneous rocks from Mars that are available to us in the form of Martian meteorites. Once the baseline Fe isotope fractionation in these rocks are established, it will be possible to determine any Fe isotopic variation because of lowtemperature aqueous processes including biogenic activities. Previous research has recognized an evaporite sequence preserved within some of the Martian meteorites [e.g., 2]. This finding highlighted different alteration processes affecting Martian meteorites and Mars, and has important implications for the timing, extent and duration of hydrous activity at the planet’s surface. Methodology and Samples: The goals of the project are pursued through a detailed study of the bulk, elemental and isotopic composition of components within Martian meteorites. Iron is an important constituent of the rock-forming minerals that are produced at the elevated temperatures experienced during magma genesis. Iron has four stable isotopes (54, 56, 57 and 58) and is also an important constituent of secondary minerals produced by alteration of primary minerals, occurring in clay minerals and carbonates. Kinetic, equilibrium and nuclear processes fractionate the isotopes, in the same way as is commonly observed for light elements. Iron isotopes have also been shown to be fractionated by biological processes, and thus have potential in providing bio-signatures in a sample. Previous to this study, a suite of 8 Martian meteorites were analysed for their whole-rock Fe isotope composition using an MC-ICP-MS technique, which indicated limited but distinct fractionation patterns compared to terrestrial and lunar samples [3]. In the present work, we have measured iron isotope compositions of a group of Martian meteorites to ascertain variation in