A. Gould¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA.

Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth’s) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet’s temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.

Reference
Gould et al. (2014) A terrestrial planet in a ~1-AU orbit around one member of a ~15-AU binary. Science 345:46.
[doi:10.1126/science.1251527]
Reprinted with permission from AAAS

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Xuchao Zhao¹, Yangting Lin¹, Qing-Zhu Yin², Jianchao Zhang¹, Jialong Hao¹, Michael Zolensky³ and Peter Jenniskens^4,5

¹Key Laboratory of the Earth’s Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
²Department of Earth and Planetary Sciences, University of California at Davis, Davis, California, USA
³ARES, NASA Johnson Space Center, Houston, Texas, USA
⁴SETI Institute, Mountain View, California, USA
⁵NASA Ames Research Center, Moffett Field, California, USA

The Sutter’s Mill (SM) carbonaceous chondrite is a regolith breccia, composed predominantly of CM2 clasts with varying degrees of aqueous alteration and thermal metamorphism. An investigation of presolar grains in four Sutter’s Mill sections, SM43, SM51, SM2-4, and SM18, was carried out using NanoSIMS ion mapping technique. A total of 37 C-anomalous grains and one O-anomalous grain have been identified, indicating an abundance of 63 ppm for presolar C-anomalous grains and 2 ppm for presolar oxides. Thirty-one silicon carbide (SiC), five carbonaceous grains, and one Al-oxide (Al₂O₃) were confirmed based on their elemental compositions determined by C-N-Si and O-Si-Mg-Al isotopic measurements. The overall abundance of SiC grains in Sutter’s Mill (55 ppm) is consistent with those in other CM chondrites. The absence of presolar silicates in Sutter’s Mill suggests that they were destroyed by aqueous alteration on the parent asteroid. Furthermore, SM2-4 shows heterogeneous distributions of presolar SiC grains (12–54 ppm) in different matrix areas, indicating that the fine-grained matrix clasts come from different sources, with various thermal histories, in the solar nebula.

Reference
Zhao X, Lin Y, Yin Q-Z, Zhang J, Hao J, Zolensky M and Jenniskens P (in press) Presolar grains in the CM2 chondrite Sutter’s Mill. Meteoritics & Planetary Science
[doi:10.1111/maps.12289]
Published by arrangement with John Wiley & Sons

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Vincent R. Eke^a, Sarah A. Bartram^a, David A. Lane^a, David Smith^a, Luis F.A. Teodoro^b

^aInstitute for Computational Cosmology, Department of Physics, Durham University, Science Laboratories, South Road, Durham DH1 3LE, U.K
^bBAER, Planetary Systems Branch, Space Science and Astrobiology Division, MS: 245-3, NASA Ames Research Center, Moffett Field, CA 94035-1000, U.S.A

Circular Polarisation Ratio (CPR) mosaics from Mini-SAR on Chandrayaan-1 and Mini-RF on LRO are used to study craters near to the lunar north pole. The look direction of the detectors strongly affects the appearance of the crater CPR maps. Rectifying the mosaics to account for parallax also significantly changes the CPR maps of the crater interiors. It is shown that the CPRs of crater interiors in unrectified maps are biased to larger values than crater exteriors, because of a combination of the effects of parallax and incidence angle. Using the LOLA Digital Elevation Map (DEM), the variation of CPR with angle of incidence has been studied. For fresh craters, CPR ∼0.7 with only a weak dependence on angle of incidence or position interior or just exterior to the crater, consistent with dihedral scattering from blocky surface roughness. For anomalous craters, the CPR interior to the crater increases with both incidence angle and distance from the crater centre. Central crater CPRs are similar to those in the crater exteriors. CPR does not appear to correlate with temperature within craters. Furthermore, the anomalous polar craters have diameter-to-depth ratios that are lower than those of typical polar craters. These results strongly suggest that the high CPR values in anomalous polar craters are not providing evidence of significant volumes of water ice. Rather, anomalous craters are of intermediate age, and maintain sufficiently steep sides that sufficient regolith does not cover all rough surfaces.

Reference
Eke VR, Bartram SA, Lane DA, Smith D and Teodoro LFA (in press) Lunar polar craters – icy, rough or just sloping? Icarus
[doi:10.1016/j.icarus.2014.06.021]
Copyright Elsevier

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Patricia M. Doyle^1,2, Paul F. Schofield², Andrew J. Berry^1,2, Andrew M. Walker³ and Kevin S. Knight^4,2

¹Department of Earth Science and Engineering, Imperial College London, South Kensington SW7 2AZ, U.K.
²Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, U.K.
³School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, U.K.
⁴ISIS Science Division, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, U.K.

The structures of eight synthetic samples of hibonite, with variable Ti oxidation state and Ti concentration (2.4–15.9 wt% TiO₂) that span the range reported for natural hibonite found in meteorites, were determined by Rietveld refinements of neutron powder diffraction data. Ti³⁺ was found to exclusively occupy the octahedral face-sharing M4 site irrespective of the presence or absence of Ti⁴⁺. Ti⁴⁺ partitions between the trigonal bipyramidal M2 site and the M4 site. The ratio (Ti⁴⁺ on M2):(Ti⁴⁺ on M4) appears to be constant for all the samples, with an average of 0.18(2) irrespective of the concentrations of Ti³⁺ and Ti⁴⁺. These substitutional sites were shown to be the most stable configurations for Ti in hibonite from calculations using density functional theory, although the predicted preference of Ti⁴⁺ for M4 over M2 is not as strong as is observed. This is attributed to the different Ti contents of the experimental and calculated structures and suggests that the Ti site occupancies might change between these concentrations. Furthermore, it is shown that Ti has a preference to occupy neighboring M4 sites such that Ti-Ti interactions occur with stabilization energies of 83 kJ/mol for Ti³⁺-Ti³⁺ and at least 15 kJ/mol for Ti⁴⁺-Ti⁴⁺. Features in optical spectroscopy and electron spin resonance data from meteoritic and synthetic hibonites that have been used to infer Ti³⁺/Ti⁴⁺ are shown to actually derive from these Ti-Ti interactions. The amount of Ti⁴⁺ in hibonite can be determined from the unit-cell parameters if ∑Ti is determined independently. Ti³⁺/Ti⁴⁺ in hibonite may record the oxygen fugacity (f_O2) of the early solar nebula, however, the existence of Ti³⁺-Ti³⁺ and Ti⁴⁺-Ti⁴⁺ interactions and the potential for Ti⁴⁺-Ti³⁺ interactions need to be considered when interpreting spectroscopic data in terms of Ti valence state and f_O2. Hibonite as a single-mineral oxybarometer must be used with caution due to the potential role of crystal chemistry (including Ti-Ti interactions) to stabilize Ti oxidation states independently of f_O2.

Reference
Doyle PM, Schofield PF, Berry AJ, Walker AM and Knight KS (2014) Substitution of Ti3+ and Ti4+ in hibonite (CaAl12O19). American Mineralogist 99:1369.
[doi:10.2138/am.2014.4532]
Copyright: The Mineralogical Society of America

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Christopher T. Adcock¹, Elisabeth M. Hausrath¹, Paul M. Forster^2,3, Oliver Tschauner^1,3 and Kirellos J. Sefein¹

¹Department of Geoscience, University of Nevada Las Vegas, 4505 South Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.
²Department of Chemistry, University of Nevada Las Vegas, 4505 South Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.
³HiPSEC, University of Nevada Las Vegas, 4505 South Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.

Merrillite [Ca₉NaMg(PO₄)₇] occurs as a dominant primary Ca-phosphate mineral in martian meteorites and therefore presumably also on Mars. The mineral is an important phase in exploring differences in geologic processes between Earth and Mars, and also has astrobiological implications due to its potential role as a significant source of the bio-essential nutrient phosphate. Merrillite does not occur terrestrially as a discrete mineral phase, making it difficult to obtain for Mars-relevant studies. It can, however, be synthesized from a similar terrestrial mineral, whitlockite (natural or synthetic), through dehydrogenation. Here we present methods for synthesizing relatively large quantities (0.5 g or greater per batch) of coarse crystalline (75 μm+) Mg-whitlockite, Fe-whitlockite, mixed Fe/Mg-whitlockites, and from these synthesized minerals produce Mg-merrillite, ferrous and ferric Fe-merrillite, and ferrous and ferric mixed Fe/Mg-merrillite. Chemistry and atomic structures of synthesized Fe- and mixed Fe/Mg-whitlockite and ferrous and ferric Fe- and mixed Fe/Mg- merrillite resulting from single-crystal X-ray diffraction, infrared spectroscopy, and electron microprobe analyses are presented. We also present a mechanism for maintaining charge balance during the formation of merrillite from whitlockite. Our results shed light on these mineral structures for future martian studies, and provide methods for creating coarse crystalline merrillite for use in Mars-relevant thermodynamic, kinetic, soil/dust simulant, crystallographic, astrobiological, and other studies.

Reference
Adcock CT, Hausrath EM, Forster PM, Tschauner O and Sefein KJ (2014) Synthesis and characterization of the Mars-relevant phosphate minerals Fe- and Mg-whitlockite and merrillite and a possible mechanism that maintains charge balance during whitlockite to merrillite transformation. American Mineralogist 99:1221.
[doi:10.2138/am.2014.4688]
Copyright: The Mineralogical Society of America

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Ema Bobocioiu and Razvan Caracas

Laboratoire de Géologie de Lyon (LGLTPE) CNRS UMR 5276, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon 46, allée d’Italie, 69364 Lyon, France

We study hydrated magnesium sulfate minerals from first-principles calculations based on density-functional theory. We determine the heat of hydration for MgSO₄·nH₂O, compute the Raman and infrared spectra for several phases and calculate the S isotope partitioning as a function of hydration. We find that epsomite and meridianiite with, respectively, n = 7 andn = 11 water molecules per MgSO₄ unit are particularly stable with respect to other individual or combinations of hydration states. The Raman spectra of all phases present clear SO₄ features that are easily identifiable. We use this to show one can use the vibrational spectroscopic information as an identification tool in a remote environment, like the martian surface. We discuss the character and atomic displacement pattern of all vibration modes and compute the ³⁴S/³²S partitioning; this work shows that hydration favors enrichment in the lighter S isotope ³²S with respect to the heavier ³⁴S, which is accumulated in the less hydrous structures. We show for the first time that the signature of ³⁴S/³²S partitioning could be observed by in situ spectroscopy on the surface of Mars. Moreover this can be related to the diurnal cycle of hydration and dehydration and hence it can improve the modeling of the water circulation on Mars.

Reference
Bobocioiu E and Caracas R (2014) Stability and spectroscopy of Mg sulfate minerals: Role of hydration on sulfur isotope partitioning. American Mineralogist 99:1216.
[doi:10.2138/am.2014.4632]
Copyright: The Mineralogical Society of America

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Valerie M. Tu¹, Elisabeth M. Hausrath¹, Oliver Tschauner^1,2, Valentin Iota² and Gerald W. Egeland³

¹Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.
²HiPSEC, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.
³Department of Mechanical Engineering, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154, U.S.A.

Phosphate is an essential nutrient for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. The amorphous fraction of martian soils has also been shown to be enriched in P, and amorphous phosphates are therefore also likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe-phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors from steady state concentrations of Al, Fe, and P. A pH-dependent rate law, log R = log k – npH was determined from the dissolution rates, where R is the dissolution rate, k is the intrinsic rate constant, and n is the reaction order with respect to H+. For amorphous Al-phosphate, log k = −6.539 ± 1.529 and n = 2.391 ± 0.493. For amorphous Fe-phosphate, log k= −13.031 ± 0.558 and n = 1.376 ± 0.221. The amorphous Al-phosphate dissolves stoichiometrically under all experimental conditions measured, and the amorphous Fe-phosphate dissolves non-stoichiometrically, approaching stoichiometric dissolution as pH decreases, due potentially to Fe oxyhydroxides precipitating and armoring grain surfaces. Perhaps due to these effects, amorphous Al-phosphate dissolution rates are approximately three orders of magnitude faster than the amorphous Fe-phosphate dissolution rates measured under these experimental conditions. Amorphous Al-phosphate dissolution rates measured in this study are also faster than published dissolution rates for the crystalline Al-phosphate variscite. The rapid dissolution rates measured in this study therefore suggest that, if these phases are present on Mars, phosphate would be rapidly released into acidic environments.

Reference
Tu VM, Hausrath EM, Tschauner O, Iota V and Egeland GW (2014) Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars. American Mineralogist 99:1206.
[doi:10.2138/am.2014.4613]
Copyright: The Mineralogical Society of America

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Pablo Sobron^1,2,3, Janice L. Bishop^1,3, David F. Blake³, Bin Chen³ and Fernando Rull⁴

¹SETI Institute, 189 Bernardo Avenue, Mountain View, California 94043, U.S.A.
²MalaUva Labs, 822 Allen Avenue, St. Louis, Missouri 63104, U.S.A.
³NASA Ames Research Center, Moffett Field, California 94035, U.S.A.
⁴Unidad Asociada UVA-Centro de Astrobiología, Edificio INDITI, Av.Francisco Valles 8, Parque Tecnologico de Boecillo, Parcela 203, Boecillo 47151, Spain

We have characterized complex iron- and sulfate-bearing samples from Rio Tinto (Spain) using X-ray diffraction (XRD), visible-near infrared reflectance (VNIR) spectroscopy, and laser Raman spectroscopy (LRS). Samples were collected for this study from the Peña de Hierro region of Rio Tinto because this site represents a natural acidic environment that is a potential analog for such environments on Mars. We report an evaluation of the capabilities of these three techniques in performing detailed mineralogical characterization of potential Mars-like samples from a natural acidic terrestrial environment. Sulfate minerals found in these samples include gypsum, jarosite, and copiapite, and iron hydroxide bearing minerals found include goethite and ferrihydrite. These sulfate and iron hydroxide/oxyhydroxide minerals were detected by XRD, VNIR, and LRS. Minor quartz was identified in some samples by XRD as well, but was not identified using VNIR spectroscopy. Coordinating the results from these three techniques provides a complete picture of the mineralogical composition of the samples. Field instruments were used for this study to mimic the kinds of analyses that could be performed in the field or on martian rovers.

Reference
Sobron P, Bishop JL, Blake DF, Chen B and Rull F (2014) Natural Fe-bearing oxides and sulfates from the Rio Tinto Mars analog site: Critical assessment of VNIR reflectance spectroscopy, laser Raman spectroscopy, and XRD as mineral identification tools. American Mineralogist 99:1199.
[doi:10.2138/am.2014.4595]
Copyright: The Mineralogical Society of America

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A. A. Pavlov¹, A. K. Pavlov^2,3, V. M. Ostryakov³, G. I. Vasilyev², P. Mahaffy¹ and A. Steele⁴

¹Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
²A. F. Ioffe Physico-Technical Institute of Russian Academy of Sciences, St. Petersburg, Russia
³St. Petersburg State Polytechnical University, St. Petersburg, Russia
⁴Geophysical Laboratory, Carnegie Institute of Washington, Washington, District of Columbia, USA

¹³C/¹²C and ¹⁵N/¹⁴N isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce ¹³C and¹⁵N isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both ¹³C and ¹⁵N due to galactic cosmic rays (GCRs) exposure can vary within 1.5–6 atoms/cm³/s depending on rocks’ depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5–10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the “light,” potentially “biological” ¹³C/¹²C ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e.g., 100 million years), cosmogenic changes in ¹⁵N/¹⁴N ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (¹⁵N/¹⁴N). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed.

Reference
Pavlov AA, Pavlov AK, Ostryakov VM, Vasilyev GI, Mahaffy P and Steele A (in press) Alteration of the carbon and nitrogen isotopic composition in the Martian surface rocks due to cosmic ray exposure. Journal of Geophysical Research: Planets
[doi:10.1002/2014JE004615]
Published by arrangement with John Wiley & Sons

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Bruce G. Bills, Sami W. Asmar, Alexander S. Konopliv, Ryan S. Park, Carol A. Raymond

Jet Propulsion Laboratory, California Institute of Technology,Pasadena, CA 91109

We examine the gravity and topography of the asteroid 4 Vesta, as recently revealed by the Dawn mission. The observed gravity is highly correlated with the observed topography, and suggests little lateral variation in density. The variance spectra of both gravity and topography follow power laws which are very similar to those seen for the Moon, Mars, Venus, and Earth. A significant way in which Vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic, with more north-south variation than east-west variation. Rapid rotation plausibly contributes to this anisotropy, but only at harmonic degree two. The remainder of the anisotropy appears related to the large impacts which formed the Rheasilvia and Veneneia basins. We note that, as usual, gravitational inverse problems are non-unique. While the observed gravity and topography of Vesta do not preclude existance of a metallic core, they certainly do not require it.

Reference
Bills BG, Asmar SW, Konopliv AS, Park RS and Raymond CA (in press) Harmonic and statistical analyses of the gravity and topography of Vesta. Icarus
[doi:10.1016/j.icarus.2014.05.033]
Copyright Elsevier

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