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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