Ann M. Ollila¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Princeton University, Princeton, NJ 08540, USA

The ChemCam instrument package on the Mars rover, Curiosity, provides new capabilities to probe the abundances of certain trace elements in the rocks and soils on Mars using the laser-induced breakdown spectroscopy technique. We focus on detecting and quantifying Li, Ba, Rb, and Sr in targets analyzed during the first 100 sols, from Bradbury Landing Site to Rocknest. Univariate peak area models and multivariate partial least squares models are presented. Li, detected for the first time directly on Mars, is generally low (<15 ppm). The lack of soil enrichment in Li, which is highly fluid mobile, is consistent with limited influx of subsurface waters contributing to the upper soils. Localized enrichments of up to ~60 ppm Li have been observed in several rocks but the host mineral for Li is unclear. Bathurst_Inlet is a fine-grained bedrock unit in which several analysis locations show a decrease in Li and other alkalis with depth, which may imply that the unit has undergone low-level aqueous alteration that has preferentially drawn the alkalis to the surface. Ba (~1000 ppm) was detected in a buried pebble in the Akaitcho sand ripple and it appears to correlate with Si, Al, Na, and K, indicating a possible feldspathic composition. Rb and Sr are in the conglomerate Link at abundances >100 ppm and >1000 ppm, respectively. These analysis locations tend to have high Si and alkali abundances, consistent with a feldspar composition. Together, these trace element observations provide possible evidence of magma differentiation and aqueous alteration.

Reference
Ann M. Ollila et al. (in press) Trace element geochemistry (Li, Ba, Sr, and Rb) using Curiosity’s ChemCam: Early results for Gale crater from Bradbury Landing Site to Rocknest. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004517]
Published by arrangement with John Wiley & Sons

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Nancy L. Chabot^a, E. Alex Wollack^b, Rachel L. Klima^a and Michelle E. Minitti^a

^aThe Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
^bPrinceton University, Princeton, NJ 08540, USA

The recent discovery of high S concentrations on the surface of Mercury by spacecraft measurements from the MESSENGER mission provides the potential to place new constraints on the composition of Mercuryʼs large metallic core. In this work, we conducted a set of systematic equilibrium metal–silicate experiments that determined the effect of different metallic compositions in the Fe–S–Si system on the S concentration in the coexisting silicate melt. We find that metallic melts with a range of S and Si combinations can be in equilibrium with silicate melts with S contents consistent with Mercuryʼs surface, but that such silicate melts contain Fe contents lower than measured for Mercuryʼs surface. If Mercuryʼs surface S abundance is representative of the planetʼs bulk silicate composition and if the planet experienced metal–silicate equilibrium during planetary core formation, then these results place boundaries on the range of possible combinations of Si and S that could be present as the light elements in Mercuryʼs core and suggest that Mercuryʼs core likely contains Si. Except for core compositions with extreme abundances of Si, bulk Mercury compositions calculated by using the newly determined range of potential S and Si core compositions do not resemble primitive meteorite compositions.

Reference
Chabot NL, Wollack EA, Klima RL and Minitti ME (2014) Experimental constraints on Mercuryʼs core composition. Earth and Planetary Science Letters 390:199–208.
[doi:10.1016/j.epsl.2014.01.004]
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N.G. Rudraswami^a, M. Shyam Prasad^a, J.M.C. Plane^b, T. Berg^c, W. Feng^b and S. Balgar^a

^aNational Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403 004, India
^bSchool of Chemistry, University of Leeds, Leeds LS29JT, UK
^cInstitut für Physik, Johannes Gutenberg-Universität, Staudingerweg 7, D-55128 Mainz, Germany

Out of the three basic cosmic spherule types collected from the seafloor, RMNs (Refractory Metal Nuggets) have been reported from I-type spherules commonly, rarely from S-type spherules and never from the G-type spherules. Nuggets in the I-type cosmic spherules have formed by melting and complete oxidation during atmospheric entry, whereas no clear understanding emerged so far regarding the formation of the rare nuggets in S-type spherules. We collected cosmic spherules by raking the deep seafloor with magnets, and carried out systematic and sequential grinding, polishing and electron microscopic investigations on 992 cosmic spherules to identify RMNs. Fifty-four nuggets (RMNs) are identified, out of which 23, 26, and 5 nuggets are recovered from 23 I-, 21 S- and 5 G-type cosmic spherules, respectively.
The nuggets in all the three spherule types follow a pattern indicative of their formation by metal segregation during atmospheric entry due to heating and oxidation, however, there are differences in their elemental distribution patterns. The refractory metal elements (RMEs) in the I-type spherules show a sequence of volatilization form a chondritic source, however, the relatively volatile RMEs in these spherules seem to be either depleted or distributed in numerous smaller nuggets. However, RMNs in the G-type spherules show closer conformity to CI chondrites and do not have a large volatile RME depletion. Whereas, the RMEs in the nuggets found in the S-type spherules are enriched in the volatile as well as the refractory elements. Also all the spherules show enrichment patterns and elemental ratios that are close to CI composition for refractory elements suggesting a common mechanism of formation. Pulse heating during atmospheric entry seems to be an efficient mechanism for RME segregation into nuggets. The patterns of RME enrichment and elemental ratios when compared with the nuggets in CAIs, show marked variations, outlining their differences in the process of formation. In addition, we also discovered a fremdling-like object in a cosmic spherule which has a nugget encased in Fe-Ni and sulfide phases, similar to those typically observed in CAIs of CV or CO chondrites. The atmospheric entry for this rare cosmic spherule appears to have taken place at a high zenith angle with a low entry velocity, so that its volatile phases are well preserved.

Reference
Rudraswami NG, Prasad MS, Plane JMC, Berg T, Feng W and Balgar S (in press) Refractory Metal Nuggets In Different Types Of Cosmic Spherules. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.01.026]
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Matthew R.M. Izawa^a, Edward A. Cloutis^a, Daniel M. Applin^a, Michael A. Craig^b, Paul Mann^a and Matthew Cuddy^a

^aHyperspectral Optical Sensing for Extraterrestrial Reconnaissance Laboratory, Dept. Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba R3B 2E9, Canada
^bDepartment of Earth Sciences/Centre for Planetary Science and Exploration, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada

Reflectance spectroscopy of Apollo lunar soil samples curated in an air- and water-free, sealed environment since recovery and return to Earth has been carried out under water-, oxygen-, CO₂– and organic-controlled conditions. Spectra of these pristine samples contain features near 3 μm wavelength similar to those observed from the lunar surface by the Chandrayaan-1 Moon Mineralogy Mapper (M³), Cassini Visual and Infrared Mapping Spectrometer (VIMS), and Deep Impact Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) High-Resolution Instrument (HRI) instruments. Spectral feature characteristics and inferred OH/H₂O concentrations are within the range of those observed by spacecraft instruments. These findings confirm that the 3 μm feature from the lunar surface results from the presence of hydration in the form of bound OH and H₂O. Implantation of solar wind H⁺ appears to be the most plausible formation mechanism for most of the observed lunar OH and H₂O.

Reference
Izawa MRM, Cloutis EA, Applin DM, Craig MA, Mann P and Cuddy M (2014) Laboratory spectroscopic detection of hydration in pristine lunar regolith. Earth and Planetary Science Letters 390:157–164.
[doi:10.1016/j.epsl.2014.01.007]
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Jessica J. Barnes^a,b, Romain Tartèse^a, Mahesh Anand^a,b, Francis M. McCubbin^c, Ian A. Franchi^a, Natalie A. Starkey^a, Sara S. Russell<sup>b

a</sup>Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
^bDepartment of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
^cInstitute of Meteoritics, University of New Mexico, 200 Yale Blvd SE, Albuquerque, NM, USA

The recent discoveries of hydrogen (H) bearing species on the lunar surface and in samples derived from the lunar interior have necessitated a paradigm shift in our understanding of the water inventory of the Moon, which was previously considered to be a ‘bone-dry’ planetary body. Most sample-based studies have focused on assessing the water contents of the younger mare basalts and pyroclastic glasses, which are partial-melting products of the lunar mantle. In contrast, little attention has been paid to the inventory and source(s) of water in the lunar highlands rocks which are some of the oldest and most pristine materials available for laboratory investigations, and that have the potential to reveal the original history of water in the Earth–Moon system. Here, we report in-situ measurements of hydroxyl (OH) content and H isotopic composition of the mineral apatite from four lunar highlands samples (two norites, a troctolite, and a granite clast) collected during the Apollo missions. Apart from troctolite in which the measured OH contents in apatite are close to our analytical detection limit and its H isotopic composition appears to be severely compromised by secondary processes, we have measured up to ~2200 ppm OH in the granite clast with a weighted average δD of , and up to ∼3400 ppm OH in the two norites (77215 and 78235) with weighted averageδD values of −281±49‰ and −27±98‰, respectively. The apatites in the granite clast and the norites are characterised by higher OH contents than have been reported so far for highlands samples, and have H isotopic compositions similar to those of terrestrial materials and some carbonaceous chondrites, providing one of the strongest pieces of evidence yet for a common origin for water in the Earth–Moon system. In addition, the presence of water, of terrestrial affinity, in some samples of the earliest-formed lunar crust suggests that either primordial terrestrial water survived the aftermath of the putative impact-origin of the Moon or water was added to the Earth–Moon system by a common source immediately after the accretion of the Moon.

Reference
Barnes JJ, Tartèse R, Anand M, McCubbin FM, Franchi IA, Starkey NA, Russell SS (2014) The origin of water in the primitive Moon as revealed by the lunar highlands samples. Earth and Planetary Science Letters390:244–252.
[doi:10.1016/j.epsl.2014.01.015]
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L. J. Hallis^a,b,c, M. Anand^b,c, S. Strekopytov^c

^aHawai‘i Institute of Geophysics and Planetology, Pacific Ocean Science & Technology (POST) Building, University of Hawai‘i, 1680 East-West Road, Honolulu, HI 96822, US
^bDepartment of Physical Sciences, CEPSAR, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
^cDepartment of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom

The heterogeneous-source model of mare basalt formation indicates that Lunar Magma Ocean (LMO) overturn produced an uneven mixture of early-formed olivine and pyroxene, and late-formed, ilmenite-rich cumulates, which subsequently partially melted to give rise to mare magmas. These heterogeneous cumulate source regions would not only have been characterised by different mineral modal abundances, but also by different trace element compositions. The aim of this work was to investigate the petrology and geochemistry of a diverse suite of Apollo mare basalts, and utilise trace-element modelling in order to understand their petrogenetic history. Chemical modelling confirms that the mare basalts were produced by relatively small degrees of partial melting (< 10%) of the LMO cumulates, and that the dominant melting type (batch vs. fractional) varies among different basalt groups. Similarly, single-source mineralogy cannot be applied to all mare basalt types, confirming that the lunar mantle was heterogeneous at the time of generation of mare magmas. Plagioclase is not required in the source of most mare basalts, with the notable exception of the Apollo 14 high-Al basalts. Addition of more than 1% plagioclase to the source of other basalts produces weaker negative Eu anomalies than those observed in the samples. AFC calculations demonstrate the compositional differences between materials assimilated into the Apollo 14 high-Al and Apollo 11 high-K mare basalt partial melts, highlighting the complexities of mare basalt petrogenesis.

Reference
Hallis LJ, Anand M and Strekopytov S (in press) Trace-element modelling of mare basalt parental melts: Implications for a heterogeneous lunar mantle. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.01.012]
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Isabel Egea-González^a and Javier Ruiz^b

^aInstituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
^bDepartamento de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040 Madrid, Spain

Mercury is covered by a megaregolith layer, which constitutes a poor thermally conducting layer that must have an influence on the thermal state and evolution of the planet, although most thermal modeling or heat flow studies have overlooked it. In this work we have calculated surface heat flows and subsurface temperatures from the depth of thrust faults associated with several prominent lobate scarps on Mercury, valid for the time of the formation of these scarps, by solving the heat equation and taking into account the insulating effects of a megaregolith layer. We conclude that megaregolith insulation could have been an important factor limiting heat loss and therefore interior cooling and contraction of Mercury. As Mercurian megaregolith properties are not very well known, we also analyze the influence of these properties on the results, and discuss the consequences of imposing the condition that the total radioactive heat production must be lower than the total surface heat loss (this is, the Urey ratio, Ur, must be lower than 1) in a cooling and thermally contracting planet such as Mercury at the time of scarp emplacement. Our results show that satisfying the condition of Ur < 1 implies that the average abundances of heat-producing elements silicate layer is 0.4 times or less the average surface value, placing an upper bound on the bulk content of heat producing elements in Mercury’s interior.

Reference
Egea-González I and Ruiz J (in press) Influence of an insulating megaregolith on heat flow and crustal temperature structure of Mercury. Icarus
[doi:10.1016/j.icarus.2014.01.024]
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Samuel P. Kounaves^a, Nikos A. Chaniotakis^b, Vincent F. Chevrier^c, Brandi L. Carrier^a, Kaitlyn E. Folds^a, Victoria M. Hansen^a, Kyle M. McElhoney^a, Glen D. O’Neil^a, Andrew W. Weber^a

^aDepartment of Chemistry, Tufts University, Medford, MA, 02155, USA
^bDepartment of Chemistry, University of Crete, 71003 Iraklion, Crete, Greece
^cArkansas Center for Space and Planetary Science, University of Arkansas, Fayetteville, AK 72701, USA

In 2008 the Phoenix Mars lander Wet Chemistry Laboratory (WCL) measured 0.6 wt% of perchlorate (ClO₄^–) in the martian soil. A crucial question remaining unanswered is the identity of the parent salt phase(s) of the ClO₄^–. Due to the ClO₄^– ion’s high solubility and stability, its distribution, chemical forms, and interactions with water, could reveal much about the aqueous history of the planet. Until now, the presence of Ca(ClO₄)₂ as a parent salt has been considered unlikely because based on its eutectic point and model calculations, highly insoluble calcium carbonates and sulfates would serve as sinks for Ca²⁺ rather than Ca(ClO₄)_2. Thus, the dominant ClO₄^– parent salt has been assumed to be a hydrated form of Mg(ClO₄)₂. Here we report on the results of a new refined analysis of the Phoenix WCL sensor data, post-flight experiments run on a flight-spare WCL unit, and numerous laboratory analyses. The results show that the response of the Ca²⁺ sensor is extremely sensitive to the counter ion of the ClO₄^– salt, and that addition of martian soil to the Phoenix WCL that contained only Mg(ClO₄)₂ or Ca(ClO₄)₂ would have produced a very different response than what was observed on Mars. A series of analyses were run with Ca²⁺ sensors and calibration solutions identical to those used on Phoenix, and with a Mars simulant formulation known to give the same results as on Mars. The response of the Ca²⁺ sensor at various ratios of added Mg(ClO₄)₂ to Ca(ClO₄)₂ gave the best fit to the Phoenix data with a sample containing ∼ 60% Ca(ClO₄)₂ and 40% Mg(ClO₄)₂. These results suggest that the Ca(ClO₄)₂ in the Phoenix soil has not been in contact with liquid water and thus did not form by evaporation or sublimation processes. Had the highly soluble Ca(ClO₄)₂ come into contact with liquid water, then the presence of soluble sulfates would have, on evaporation formed only CaSO₄. The presence of Ca(ClO₄)₂ and Mg(ClO₄)₂ phases at roughly the CaCO₃ to MgCO₃ ratio suggests that since their production, the ClO₄^–phases have remained in a severely arid environment, with minimal or no liquid water interaction. The formation of the Ca(ClO₄)₂ and Mg(ClO₄)₂ is also consistent with the interaction of atmospherically deposited HClO₄ with Ca- and Mg-carbonates and may also contribute to CO₂ enrichment of ¹⁸O and may contribute in explaining why carbonates on the surface are at much lower levels than expected from an earlier global wet and warm period.

Reference
Kounaves SP, Chaniotakis NA, Chevrier VF, Carrier BL, Folds KE, Hansen VM, McElhoney KM, O’Neil GD and Weber AW (in press) Identification of the perchlorate parent salts at the Phoenix Mars landing site and possible implications. Icarus
[doi:10.1016/j.icarus.2014.01.016]

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Paul Douglas Archer Jr.¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Jacobs, NASA Johnson Space Center, Houston, Texas, USA

The Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) rover Curiosity detected evolved gases during thermal analysis of soil samples from the Rocknest aeolian deposit in Gale Crater. Major species detected (in order of decreasing molar abundance) were H₂O, SO₂, CO₂, and O₂, all at the µmol level, with HCl, H₂S, NH₃, NO, and HCN present at the tens to hundreds of nmol level. We compute weight % numbers for the major gases evolved by assuming a likely source and calculate abundances between 0.5 and 3 wt.%. The evolution of these gases implies the presence of both oxidized (perchlorates) and reduced (sulfides or H-bearing) species as well as minerals formed under alkaline (carbonates) and possibly acidic (sulfates) conditions. Possible source phases in the Rocknest material are hydrated amorphous material, minor clay minerals, and hydrated perchlorate salts (all potential H₂O sources), carbonates (CO₂), perchlorates (O₂ and HCl), and potential N-bearing materials (e.g., Martian nitrates, terrestrial or Martian nitrogenated organics, ammonium salts) that evolve NH₃, NO, and/or HCN. We conclude that Rocknest materials are a physical mixture in chemical disequilibrium, consistent with aeolian mixing, and that although weathering is not extensive, it may be ongoing even under current Martian surface conditions.

Reference
Archer PD Jr.(in press) Abundances and implications of volatile-bearing species from evolved gas analysis of the Rocknest aeolian deposit, Gale Crater, Mars. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004493]
Published by arrangement with John Wiley & Sons

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F. E. DeMeo^1,2 and B. Carry^3,4

¹Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-16, Cambridge, Massachusetts 02138, USA
²Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
³Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, UMR8028 CNRS, 77 avenue Denfert-Rochereau, 75014 Paris, France
⁴European Space Astronomy (ESA) Centre, PO Box 78, Villanueva de la Cañada 28691, Madrid, Spain

We are still seeking a copyright agreement with Nature to display their abstracts.

Reference
DeMeo FE and Carry B (2014) Solar System evolution from compositional mapping of the asteroid belt. Nature 505:629–634.
[doi:10.1038/nature12908]

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