¹J. P. Grotzinger et al. (>10)*
¹Division of Geologic and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
*Find the extensive, full author and affiliation list on the publishers Website

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

Reference
Grotzinger JP et al. (2015) Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars. Science 350, 6257
Link to Article [DOI: 10.1126/science.aac7575]
Reprinted with permission from AAAS

^1,2James Badro, ³John P. Brodholt, ^1,2Hélène Piet, ¹Julien Siebert, ⁴Frederick J. Ryerson
¹Institut de Physique du Globe de Paris, Sorbonne Paris Cité, UMR CNRS 7154, 75005 Paris, France
²Earth and Planetary Science Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
³Department of Earth Sciences, University College London, London WC1E 6BT, United Kingdom;
⁴Lawrence Livermore National Laboratory, Livermore, CA 94550

We combine, for the first time to our knowledge, two approaches to study Earth’s core composition: a geochemical approach based on trace element depletion in the mantle and a geophysical approach based on a seismically lighter and faster (than pure iron−nickel) core. The joint approach allows making strong statements; first of all, as opposed to the current belief, Earth must have accreted material that is more oxidized than the present-day mantle, similar to that of planetesimals such as 4-Vesta, and got reduced to its present state during core formation. Secondly, core light-element concentrations in those conditions are 2.7% to 5% oxygen alongside 2% to 3.6% silicon; the oxygen concentrations in the core are higher than previously thought, and, conversely, silicon concentrations are lower than previous estimates.

Reference
Badro J, Brodholt JP, Piet H, Siebert J, Ryerson FR (2015) Core formation and core composition from coupled geochemical and geophysical constraints. Proceedings of the National Academy of Sciences 112, 12310-12314
Link to Article [doi:10.1073/pnas.1505672112]

^1,2Annemarie E. Pickersgill, ¹Roberta L. Flemming,^1,3Gordon R. Osinski
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
²Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada
³School of Geographical & Earth Sciences, University of Glasgow, Lilybank Gardens, Glasgow, UK

Studies of shock metamorphism of feldspar typically rely on qualitative petrographic observations, which, while providing invaluable information, can be difficult to interpret. Shocked feldspars, therefore, are now being studied in greater detail by various groups using a variety of modern techniques. We apply in situ micro-X-ray diffraction (μXRD) to shocked lunar and terrestrial plagioclase feldspar to contribute to the development of a quantitative scale of shock deformation for the feldspar group. Andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada, and anorthite from Earth’s Moon, returned during the Apollo program, were examined using optical petrography and assigned to subgroups of the optical shock level classification system of Stöffler (1971). Two-dimensional μXRD patterns from the same samples revealed increased peak broadening in the chi dimension (χ), due to strain-related mosaicity, with increased optical signs of deformation. Measurement of the full width at half maximum along χ (FWHMχ) of these peaks provides a quantitative way to measure strain-related mosaicity in plagioclase feldspar as a proxy for shock level.

Reference
Pickersgill AE, Flemming RL, Osinski GR (2015) Toward quantification of strain-related mosaicity in shocked lunar and terrestrial plagioclase by in situ micro-X-ray diffraction. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12514]
Published by arrangement with John Wiley & Sons

^1,2Jennifer Buz,^1,3Benjamin P. Weiss,^3,4Sonia M. Tikoo,^3,4David L. Shuster,⁵Jérôme Gattacceca,¹Timothy L. Grove
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
³Department of Earth and Planetary Science, University of California, Berkeley, CA, USA
⁴Berkeley Geochronology Center, Berkeley, CA, USA
⁵CNRS, Aix-Marseille University, Aix-en-Provence, France

Recent paleomagnetic studies of Apollo samples have established that a core dynamo existed on the Moon from at least 4.2 to 3.56 billion years ago (Ga). Because there is no lunar dynamo today, a longstanding mystery has been the origin of magnetization in very young lunar samples [<~200 million years old (Ma)]. Possible sources of this magnetization include transient fields generated by meteoroid impacts, remanent fields from nearby rocks magnetized during an earlier dynamo epoch, a weak late dynamo, and spontaneous remanence formed in a near-zero field. To further understand the source of the magnetization in young lunar samples, we conducted paleomagnetic, petrographic, and 40Ar/39Ar geochronometry analyses on a young impact melt glass rind from the exterior of ~3.35 Ga mare basalt 12017. Cosmic ray track densities and our 40Ar/39Ar and cosmogenic 38Ar analyses constrain the glass formation age to be 10 μT) core dynamo field nor impact-generated fields.

Reference
Buz J, Weiss BP, Tikoo SM, Shuster DL, Gattacceca J, Grove TL (2015) Magnetism of a Very Young Lunar Glass. Journal of Geophysical Research (Planets)
Link to Article [DOI: 10.1002/2015JE004878]
Published by arrangement with John Wiley & Sons