ALBERT

Description: The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. We have conducted in situ hydrogen isotope (D/H) analyses of quenched and impact glasses in three Martian meteorites (Yamato 980459, EETA79001, LAR 06319) by Cameca ims-6f at Digital Terrain Models (DTM) following the methods of [1]. The hydrogen isotope analyses provide evidence for the existence of a distinct but ubiquitous water/ice reservoir (D/H = 2-3 times Earth's ocean water: Standard Mean Ocean Water (SMOW)) that lasted from at least the time when the meteorites crystallized (173-472 Ma) to the time they were ejected by impacts (0.7-3.3 Ma), but possibly much longer [2]. The origin of this reservoir appears to predate the current Martian atmospheric water (D/H equals approximately 5-6 times SMOW) and is unlikely to be a simple mixture of atmospheric and primordial water retained in the Martian mantle (D/H is approximately equal to SMOW [1]). Given the fact that this intermediate-D/H reservoir (2-3 times SMOW) is observed in a diverse range of Martian materials with different ages (e.g., SNC (Shergottites, Nakhlites, Chassignites) meteorites, including shergottites such as ALH 84001; and Curiosity surface data [3]), we conclude that this intermediate-D/H reservoir is likely a global surficial feature that has remained relatively intact over geologic time. We propose that this reservoir represents either hydrated crust and/or ground ice interbedded within sediments. Our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of Mars.

Description: Our solar system formed from nuclei produced in earlier generations of stars. Mixing in the proto-solar nebula isotopically homogenized most of this material, but some grains, called presolar grains, retain their original isotopic composition. The isotopic properties of presolar SiC grains indicate that most of the grains formed in the outflows of carbon-rich Asymptotic Giant Branch (AGB) stars. The microstructure of these presolar grains reflects the conditions of the dust formation and subsequent alteration. Early microstructural studies of SiC grains obtained by acid dissolution from meteorites show that most isotopically anomalous SiC grains have the face-centered cubic b- SiC structure. However, Daulton et al. have shown that a small fraction of sub-micron presolar SiC grains are of the hexagonal 2H polytype (a-SiC). Although the harsh chemical treatments of these grains does not alter their crystal structure, significant alteration of the surface morphology of the grains due to the acid treatments has been observed. In addition, the acid treatments may preferentially remove cracked or fissured grains, and possible sub-grains, such as graphite. By studying SiC grains isolated by physical separation and found in situ, we attempt to obtain a more complete analysis of presolar SiC microstructures, including the surface morphology, in order to address the formation and processing history of the grains. In our prior work, we reported on one in situ SiC grain (hereafter CBIS1). Here we present results from two additional grains, one in situ, and one prepared as a physical separate.