^1,2Adrien Denoeud et al. (>10)*
Proceedings of the National Academy of Sciences 113, 7745-7749 Link to Article [doi:10.1073/pnas.1512127113]
¹Laboratoire d’Utilisation de Lasers Intenses – CNRS, Ecole Polytechnique, Commissariat à l’Energie Atomique et aux Energies Alternatives, Université Paris-Saclay, F-91128 Palaiseau Cedex, France;
²Sorbonne Universités, Université Pierre et Marie Curie Paris 6, CNRS, Laboratoire d’Utilisation des Lasers Intenses, place Jussieu, 75252 Paris Cedex 05, France
*Find the extensive, full author and affiliation list on the publishers website

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.

¹Suniti Karunatillake, ²James J. Wray, ^3,4Olivier Gasnault, ⁵Scott M. McLennan, ⁵A. Deanne Rogers, ⁶Steven W. Squyres, ⁷William V. Boynton, ⁸J. R. Skok, ¹Nicole E. Button, ¹Lujendra Ojha
Journal of Geophysical Research (Planets) (in Press) Link to Article [DOI: 10.1002/2016JE005016]
¹Geology and Geophysics, Louisiana State University, Baton Rouge, LA, USA
²Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
³Université de Toulouse [UPS; OMP; IRAP], Toulouse, France
⁴CNRS [UMR 5277], Institut de Recherche en Astrophysique et Planétologie, BP, Toulouse Cedex 4, France
⁵Department of Geosciences, Stony Brook University, Stony Brook, New York, USA
⁶Department of Astronomy, Cornell University, Ithaca, New York, USA
⁷Department of Planetary Sciences, University of Arizona, AZ, USA
⁸SETI institute, CA, USA
⁹Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Published by arrangement with John Wiley & Sons

Midlatitudinal hydrated sulfates on Mars may influence brine pH, atmospheric humidity, and collectively water activity. These factors affect the habitability of the planetary subsurface and the preservation of relict biomolecules. Regolith at grain sizes smaller than gravel, constituting the bulk of the martian subsurface at regional scales, may be a primary repository of chemical alteration, mechanical alteration, and biosignatures. The Mars Odyssey Gamma Ray Spectrometer with hundreds of kilometers of lateral resolution and compositional sensitivity to decimeter depth provides unique insight into this component of the regolith, which we call soil. Advancing the globally compelling association between H2O and S established by our previous work [Karunatillake et al., 2014], we characterize latitudinal variations in the association between H and S, as well as in the hydration state of soil. Represented by H2O:S molar ratios, the hydration state of candidate sulfates increases with latitude in the northern hemisphere. In contrast, hydration states generally decrease with latitude in the south. Furthermore, we observe that H2O concentration may affect the degree of sulfate hydration more than S concentration. Limited H2O availability in soil-atmosphere exchange and in subsurface recharge could explain such control exerted by H2O on salt hydration. Differences in soil thickness, ground ice table depths, atmospheric circulation, and insolation may contribute to hemispheric differences in the progression of hydration with latitude. Our observations support chemical association of H2O with S in the southern hemisphere as suggested by Karunatillake et al. [2014], including the possibility of Fe-sulfates as a key mineral group.