¹R.S. Jackson et al. (>10)*
¹University of New Mexico, Albuquerque, NM 87131, USA
*Find the extensive, full author and affiliation list on the publishers website

The ChemCam instrument on the Mars Science Laboratory rover analyzed the rock surface, drill hole walls, tailings, and unprocessed and sieved dump piles to investigate chemical variations with depth in the first two Martian drill holes and possible fractionation or segregation effects of the drilling and sample processing. The drill sites are both in Sheepbed Mudstone, the lowest exposed member of the Yellowknife Bay formation. Yellowknife Bay is composed of detrital basaltic materials in addition to clay minerals and an amorphous component. The drill tailings are a mixture of basaltic sediments and diagenetic material like calcium sulfate veins, while the shots on the drill site surface and walls of the drill holes are closer to those pure end members. The sediment dumped from the Sample Acquisition, Processing, and Handling Subsystem is of similar composition to the tailings; however, due to the specifics of the drilling process the tailings and dump piles come from different depths within the hole. This allows the ChemCam instrument to analyze samples representing the bulk composition from different depths. On the pre-drill surfaces, the Cumberland site has a greater amount of CaO and evidence for calcium sulfate veins, than the John Klein site. However, John Klein has a greater amount of calcium sulfate veins below the surface, as seen in mapping, drill hole wall analysis, and observations in the drill tailings and dump pile. In addition, the Cumberland site does not have any evidence of variations in bulk composition with depth down the drill hole, while the John Klein site has evidence for a greater amount of CaO (calcium sulfates) in the top portion of the hole compared to the middle section of the hole, where the drill sample was collected.

Reference
Jackson RS et al. (2016) ChemCam Investigation of the John Klein and Cumberland Drill Holes and Tailings, Gale Crater, Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.026]
Copyright Elsevier

¹Paul G. Lucey, ²Benjamin T. Greenhagen, ³Eugenie Song, ⁴Jessica A. Arnold, ^1,5Myriam Lemelin, ⁴Kerri Donaldson Hanna, ⁴Neil E. Bowles, ⁶Timothy D. Glotch, ⁷David A. Paige
¹Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, 1680 East West Road, Honolulu 96822, HI USA
²Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Rd. Laurel 20723, MD USA
³Jet Propulsion Laboratory, 4800 Oak Grove Drive Pasadena Mail Stop 264-623, CA 91109 USA
⁴Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
⁵Department of Geology and Geophysics, University of Hawaii at Manoa, 1680 East West Road, Honolulu 96822, HI, USA
⁶Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA
⁷Dept. of Earth, Planetary and Space Science, University of California Los Angeles, Los Angeles 90095, CA USA

Multispectral infrared measurements by the Diviner Lunar Radiometer Experiment on the Lunar Renaissance Orbiter enable the characterization of the position of the Christiansen Feature, a thermal infrared spectral feature that laboratory work has shown is proportional to the bulk silica content of lunar surface materials. Diviner measurements show that the position of this feature is also influenced by the changes in optical and physical properties of the lunar surface with exposure to space, the process known as space weathering. Large rayed craters and lunar swirls show corresponding Christiansen Feature anomalies. The space weathering effect is likely due to differences in thermal gradients in the optical surface imposed by the space weathering control of albedo. However, inspected at high resolution, locations with extreme compositions and Christiansen Feature wavelength positions–silica-rich and olivine-rich areas–do not have extreme albedos, and fall off the albedo- Christiansen Feature wavelength position trend occupied by most of the Moon. These areas demonstrate that the Christiansen Feature wavelength position contains compositional information and is not solely dictated by albedo. An optical maturity parameter derived from near-IR measurements is used to partly correct Diviner data for space weathering influences.

Reference
Lucey PG, Greenhagen BT, Song E, Arnold JA, Lemelin M, Donaldson Hanna K, Bowles NE, Glotch TD, Paige DA (2016) Space weathering effects in Diviner Lunar Radiometer multispectral infrared measurements of the lunar Christiansen Feature: Characteristics and mitigation. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.010]
Copyright Elsevier

¹Emily A. Worsham, ¹Katherine R. Bermingham, ¹Richard J. Walker
¹Department of Geology, University of Maryland, College Park, Maryland, 20742 USA

Siderophile trace element abundances and the 187Re-187Os isotopic systematics of the metal phases of 58 IAB complex iron meteorites were determined in order to investigate formation processes and how meteorites within chemical subgroups may be related. Close adherence of 187Re-187Os isotopic data of most IAB iron meteorites to a primordial isochron indicates that the siderophile elements of most members of the complex remained closed to elemental disturbance soon after formation. Minor, presumably late-stage open-system behavior, however, is observed in some members of the sLM, sLH, sHL, and sHH subgroups. The new siderophile element abundance data are consistent with the findings of prior studies suggesting that the IAB subgroups cannot be related to one another by any known crystallization process. Equilibrium crystallization, coupled with crystal segregation, solid-liquid mixing, and subsequent fractional crystallization can account for the siderophile element variations among meteorites within the IAB main group (MG). The data for the sLM subgroup are consistent with equilibrium crystallization, combined with crystal segregation and mixing. By contrast, the limited fractionation of siderophile elements within the sLL subgroup is consistent with metal extraction from a chondritic source with little subsequent processing. The limited data for the other subgroups were insufficient to draw robust conclusions about crystallization processes involved in their formation. Collectively, multiple formational processes are represented in the IAB complex, and modeling results suggest that fractional crystallization within the MG may have been a more significant process than has been previously recognized.

Reference
Worsham EA, Bermingham KR, Walker RJ (2016) Siderophile element systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group. Geochimica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.019]
Copyright Elsevier