¹Varun G. Paul,¹David J. Wronkiewicz, ²Melanie R. Mormile, ³Jamie S. Foster
¹Department of Geological Sciences, Missouri University of Science and Technology, Rolla, Missouri.
²Department of Biological Sciences, Missouri University of Science and Technology, Rolla, Missouri.
³Department of Microbiology and Cell Science, University of Florida, Space Life Science Lab, Merritt Island, Florida.

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Reference
Paul VG, Wronkiewicz DJ, Mormile MR, Foster JS (2016) Mineralogy and Microbial Diversity of the Microbialites in the Hypersaline Storr’s Lake, the Bahamas. Astrobiology 16, 4 282-300
Link to Article [doi:10.1089/ast.2015.1326]

¹Jessica J. Barnes, ^1,2Romain Tartèse, ^1,3Mahesh Anand, ⁴Francis M. McCubbin, ⁵Clive R. Neal, ¹Ian A. Franchi
¹Planetary & Space Sciences, The Open University, Walton Hall, MK7 6AA, UK
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, 75005 Paris, France
³Earth Sciences department, Natural History Museum, London, SW7 5BD, UK
⁴NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA
⁵Department of Civil & Environmental Engineering & Earth Science, University of Notre Dame, IN 46556, USA

Current models for the Moon’s formation have yet to fully account for the thermal evolution of the Moon in the presence of H2O and other volatiles. Of particular importance is chlorine, since most lunar samples are characterised by unique heavy δ37Cl values, significantly deviating from those of other planetary materials, including Earth, for which δ37Cl values cluster around ∼0‰. In order to unravel the cause(s) of the Moon’s unique chlorine isotope signature, we performed a comprehensive study of high-precision in situ Cl isotope measurements of apatite from a suite of Apollo samples with a range of geochemical characteristics and petrologic types. The Cl-isotopic compositions measured in lunar apatite in the studied samples display a wide range of δ37Cl values (reaching a maximum value of +36‰), which are positively correlated with the amount of potassium (K), Rare Earth Element (REE) and phosphorous (P) (KREEP) component in each sample. Using these new data, integrated with existing H-isotope data obtained for the same samples, we are able to place these findings in the context of the canonical lunar magma ocean (LMO) model. The results are consistent with the urKREEP reservoir being characterised by a δ37Cl ∼+30‰. Such a heavy Cl isotope signature requires metal-chloride degassing from a Cl-enriched urKREEP LMO residue, a process likely to have been triggered by at least one large crust-breaching impact event that facilitated the transport and exposure of urKREEP liquid to the lunar surface.

Reference
Barnes JJ, Tartèse R, Anand M, McCubbin FM, Neal CR, Franchi IA (2016) Early degassing of lunar urKREEP by crust-breaching impact(s). Earth and Planetary Science Letters 447, 84–94
Link to Article [doi:10.1016/j.epsl.2016.04.036]
Copyright Elsevier

¹Janice L. Bishop, ²Elizabeth B. Rampe
¹SETI Institute, Carl Sagan Center, 189 Bernardo Ave., Mountain View, CA 94043, United States
²Aerodyne Industries, Jacobs-JETS at NASA JSC, Houston, TX 77058, United States

Layered outcrops in the Mawrth Vallis region of Mars contain the greatest diversity of aqueous alteration products on the planet, and these materials are used to infer past aqueous environments. Orbital investigations indicate Al/Si-rich clay-bearing units overly an Fe/Mg-smectite-rich unit. Many different secondary minerals have been identified in the upper Al/Si-rich clay units, but the presence of poorly crystalline phases has not been previously investigated. Identification of ∼10–30% allophane and imogolite in the clay-bearing units resolves previous mineralogical discrepancies between TES and CRISM of clay-bearing units on Mars. We demonstrate here that the poorly crystalline aluminosilicates allophane and imogolite comprise a significant portion of the uppermost stratum of the Al/Si-clay-rich units. These phases are unique to immature soils derived from volcanic ash in well-drained, mildly acidic environments on Earth, and we hypothesize that the deposits discovered here originate from supervolcanic activity in nearby Arabia Terra. The transition through time from smectite-bearing units to the uppermost allophane/imogolite unit in Mawrth Vallis signifies a change in climate from a warm and wet environment to one where water was sporadic and likely depleted rapidly.

Reference
Bishop JL, Rampe EB (2016) Evidence for a changing Martian climate from the mineralogy at Mawrth Vallis. Earth and Planetary Science Letters 448,42–48
Link to Article [doi:10.1016/j.epsl.2016.04.031]
Copyright Elsevier