K. L. Donaldson Hanna¹, L. C. Cheek¹, C. M. Pieters¹, J. F. Mustard¹, B. T. Greenhagen², I. R. Thomas³ and N. E. Bowles³

¹Department of Geological Sciences, Brown University, Providence, Rhode Island, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Atmospheric, Oceanic, and Planetary Physics, University of Oxford, Oxford, UK

Recent advancements in visible to near infrared orbital measurements of the lunar surface have allowed the character and extent of the primary anorthositic crust to be studied at unprecedented spatial and spectral resolutions. Here we assess the lunar primary anorthositic crust in global context using a spectral parameter tool for Moon Mineralogy Mapper data to identify and map Fe-bearing crystalline plagioclase based on its diagnostic 1.25 µm absorption band. This allows plagioclase-dominated rocks, specifically anorthosites, to be unambiguously identified as well as distinguished from lithologies with minor to trace amounts of mafic minerals. Low spatial resolution global mosaics and high spatial resolution individual data strips covering more than 650 targeted craters were analyzed to identify and map the mineralogy of spectrally pure regions as small as ~400 m in size. Spectrally, pure plagioclase is identified in approximately 450 targets located across the lunar surface. Diviner thermal infrared (TIR) data are analyzed for 37 of these nearly monomineralic regions in order to understand the compositional variability of plagioclase (An#) in these areas. The average An# for each spectrally pure region is estimated using new laboratory measurements of a well-characterized anorthite (An₉₆) sample. Diviner TIR results suggest that the plagioclase composition across the lunar highlands is relatively uniform, high in calcium content, and consistent with plagioclase compositions found in the ferroan anorthosites (An_94–98). Our results confirm that spectrally pure anorthosite is widely distributed across the lunar surface, and most exposures of the ancient anorthositic crust are concentrated in regions of thicker crust surrounding impact basins on the lunar nearside and farside. In addition, the scale of the impact basins and the global nature and distribution of pure plagioclase requires a coherent zone of anorthosite of similar composition in the lunar crust supporting its formation from a single differentiation event like a magma ocean. Our identifications of pure anorthosite combined with the GRAIL crustal thickness model suggest that pure anorthosite is currently observed at a range of crustal thickness values between 9 and 63 km and that the primary anorthositic crust must have been at least 30 km thick.

Reference
Donaldson Hanna KL, Cheek LC, Pieters CM, Mustard JF, Greenhagen BT, Thomas IR and Bowles NE (in press) Global assessment of pure crystalline plagioclase across the Moon and implications for the evolution of the primary crust. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004476]
Published by arrangement with John Wiley & Sons

Link to Article

D.A. Williams^a, R. Jaumann^b,c, H.Y. McSween Jr.^d, S. Marchi^e, N. Schmedemann^c, C.A. Raymond^f, C.T. Russell^g

^aSchool of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA
^bDLR, Institute of Planetary Research, Berlin, Germany
^cFreie Universität Berlin, Institut für Geowissenschaften, Germany
^dDepartment of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, 37996-1410, USA
^eSolar System Exploration Research Virtual Institute, Southwest Research Institute, Boulder, Colorado, USA
^fNASA JPL, California Institute of Technology, Pasadena, California, USA
^gUCLA, Los Angeles, California, USA

In this paper we present a time-stratigraphic scheme and geologic time scale for the protoplanet Vesta, based on global geologic mapping and other analyses of NASA Dawn spacecraft data, complemented by insights gained from laboratory studies of howardite-eucrite-diogenite (HED) meteorites and geophysical modeling. On the basis of prominent impact structures and their associated deposits, we propose a time scale for Vesta that consists of four geologic time periods: Pre-Veneneian, Veneneian, Rheasilvian, and Marcian. The Pre-Veneneian Period covers the time from the formation of Vesta up to the Veneneia impact event, from 4.6 Ga to >2.1 Ga (using the asteroid flux-derived chronology system) or from 4.6 Ga to 3.7 Ga (under the lunar-derived chronology system). The Veneneian Period covers the time span between the Veneneia and Rheasilvia impact events, from >2.1 to 1 Ga (asteroid flux-derived chronology) or from 3.7 to 3.5 Ga (lunar-derived chronology), respectively. The Rheasilvian Period covers the time span between the Rheasilvia and Marcia impact events, and the Marcian Period covers the time between the Marcia impact event until the present. The age of the Marcia impact is still uncertain, but our current best estimates from crater counts of the ejecta blanket suggest an age between ∼120-390 Ma, depending upon choice of chronology system used. Regardless, the Marcia impact represents the youngest major geologic event on Vesta. Our proposed four-period geologic time scale for Vesta is, to a first order, comparable to those developed for other airless terrestrial bodies.

Reference
Williams DA, Jaumann R, McSween Jr. HY, Marchi S, Schmedemann N, Raymond CA and Russell CT (in press) The chronostratigraphy of protoplanet vesta. Icarus
[doi:10.1016/j.icarus.2014.06.027]
Copyright Elsevier

Link to Article

Cécile Gry¹ and Edward B. Jenkins²

¹Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
²Department of Astrophysical Sciences, Princeton University Observatory, Princeton NJ 08544, USA

Aims. We offer a new, simpler picture of the local interstellar medium, made of a single continuous cloud enveloping the Sun. This new outlook enables the description of a diffuse cloud from within and brings to light some unexpected properties.
Methods. We re-examine the kinematics and abundances of the local interstellar gas, as revealed by the published results for the ultraviolet absorption lines of Mg II, Fe II, and H I.
Results. In contrast to previous representations, our new picture of the local interstellar medium consists of a single, monolithic cloud that surrounds the Sun in all directions and accounts for most of the matter present in the first 50 parsecs around the Sun. The cloud fills the space around us out to about 9 pc in most directions, although its boundary is very irregular with possibly a few extensions up to 20 pc. The cloud does not behave like a rigid body: gas within the cloud is being differentially decelerated in the direction of motion, and the cloud is expanding in directions perpendicular to this flow, much like a squashed balloon. Average H I volume densities inside the cloud vary between 0.03 and 0.1 cm^-3 over different directions. Metals appear to be significantly depleted onto grains, and there is a steady increase in depletion from the rear of the cloud to the apex of motion. There is no evidence that changes in the ionizing radiation influence the apparent abundances. Secondary absorption components are detected in 60% of the sight lines. Almost all of them appear to be interior to the volume occupied by the main cloud. Half of the sight lines exhibit a secondary component moving at about −7.2 km s^-1 with respect to the main component, which may be the signature of a shock propagating toward the cloud’s interior.

Reference
Gry C and Jenkins EB (2014) The interstellar cloud surrounding the Sun: a new perspective. Astronomy & Astrophysics 567:A58.
[doi:10.1051/0004-6361/201323342]
Reproduced with permission © ESO

Link to Article

Zhiyong Xiao¹, Zuoxun Zeng¹, Zhiyong Li¹, David M. Blair² and Long Xiao¹

¹Planetary Science Institute, China University of Geosciences, Wuhan, China
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA

We study the distribution, morphology, and geometrical properties of fractures in several young impact melt deposits on the Moon and Mercury, and the ways that these fractures may form from cooling by thermal radiation. In each impact melt complex, the topography of the underlying terrain determines the orientation of cooling fractures, such that interior fractures that formed in the relatively thick interior areas of the melt unit are wider and have a larger spacing than marginal fractures that formed in the relatively thin areas near the unit’s margins. Solid debris entrained in molten deposits provides prefracture flaws that can seed cooling fractures, but too much solid debris prevents cooling fractures from growing to macroscopic sizes. The appearance of subparallel fractures is mainly caused by subsidence of the deposits during the process of cooling and solidification. Tensile stresses caused by thermal radiation are large enough to initiate cooling fractures on both the Moon and Mercury, which may represent the initial stage of columnar joints formation, but the cooling rate caused solely by thermal radiation is not large enough to form well-organized columnar joints that feature polygonal colonnades. We therefore propose that thermal conduction and convection are the major contributors in the formation of columnar joints on planetary bodies.

Reference
Xiao Z, Zeng Z, Li Z, Blair DM and Xiao L (in press) Cooling fractures in impact melt deposits on the Moon and Mercury: Implications for cooling solely by thermal radiation. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004560]
Published by arrangement with John Wiley & Sons

Link to Article

Arya Udry^a, Nicole G. Lunning^a, Harry Y. McSween JR.^a and Robert J. Bodnar^b

^aPlanetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, TN, USA
^bDepartment of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, VA, USA

Northwest Africa (NWA) 7034 and its paired meteorites NWA 7533 and NWA 7475 are the first recognized martian polymict breccia samples. An unusual, large, subrounded clast in NWA 7034 shows a vitrophyric texture, consisting of skeletal pyroxene and olivine with mesostasis. This lithology has not been observed in the paired meteorites. It crystallized under disequilibrium conditions as indicated by its olivine and pyroxeneK_D^Fe/Mg partitioning values, as well as reversed order of crystallization and mineral compositions relative to those predicted by MELTS. We report the highest bulk Ni value (1020 ppm) measured in any known martian meteorite or martian igneous rock, suggesting an impact melt origin for the vitrophyre. Addition of 5.3-7.7% chondritic material to the target rock would account for the Ni enrichment. The bulk major and trace element abundances of the vitrophyre indicate that the protolith was not the host breccia nor any other martian meteorites. However, the clast is compositionally similar to Humphrey rock in Gusev crater analyzed by the Spirit rover and to a texturally distinct group of clasts in the paired meteorite NWA 7533. Thus, we propose that the target rock was an igneous lithology similar to Gusev basalts, which was subsequently contaminated by a chondritic impactor.

Reference
Udry A, Lunning NG, McSween JR. HY and Bodnar RJ (in press) Petrogenesis of a vitrophyre in the martian meteorite breccia NWA 7034. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.06.026]
Copyright Elsevier

Link to Article

Davide Farnocchia¹, Steven R. Chesley¹, Paul W. Chodas¹, Pasquale Tricarico², Michael S. P. Kelley³ and Tony L. Farnham³

¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²Planetary Science Institute, Tucson, AZ 85719, USA
³Department of Astronomy, University of Maryland, College Park, MD 20742, USA

Comet C/2013 A1 (Siding Spring) will experience a high velocity encounter with Mars on 2014 October 19 at a distance of 135,000 km ± 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly large nongravitational perturbations. Furthermore, we compute the required ejection velocities for the dust grains of the tail to reach Mars as a function of particle radius and density and heliocentric distance of the ejection. A comparison between our results and the most current modeling of the ejection velocities suggests that impacts are possible only for millimeter to centimeter size particles released more than 13 AU from the Sun. However, this level of cometary activity that far from the Sun is considered extremely unlikely. The arrival time of these particles spans a 20-minute time interval centered at 2014 October 19 at 20:09 TDB, i.e., around the time that Mars crosses the orbital plane of C/2013 A1. Ejection velocities larger than currently estimated by a factor >2 would allow impacts for smaller particles ejected as close as 3 AU from the Sun. These particles would reach Mars from 19:13 TDB to 20:40 TDB.

Reference
Farnocchia D, Chesley SR, Chodas PW, Tricarico P, Kelley MSP and Farnham TL (2014) Trajectory Analysis for the Nucleus and Dust of Comet C/2013 A1 (Siding Spring). The Astrophysical Journal 790:114.
[doi:10.1088/0004-637X/790/2/114]

Link to Article

This site started in October 2013 as an experiment. Although never advertised except for an announcement on the MetSoc and the German Mineralogical Society mailing lists, the site is successful, but judge for yourself. The average stats are as follows:

Number of weekly abstracts posted: ~15-25  (total until today: 700 – congratulations to all who read all of them!)
Number of journals currently covered: 21

Monthly unique users: >300
Monthly views: ~2000

Weekly unique users: ~90
Weekly views: ~400

Daily unique users (weekdays): ~25
Daily views (weekdays): ~70-100

Users from Different countries per day: 8-10
Users from >50 countries visited the webpage at least once.

Weeks don’t add up to months and days don’t add up to weeks, as unique users are reported. Users visiting the webpage more than once a week are counted as one per week. In addition, 13 followers don’t visit the site, but get the posts via email. So these need to be added to the stats above.

I started this site as I wished for such a site myself. After almost 10 months, the site still is an experiment and its continuation is unclear. In any case, I just wanted to start it. For the moment, I will continue to update it for a couple more weeks. I will keep this post on top over the next week and would like to ask whether anyone else likes this page and would be interested in continuing it. I am happy to provide any further information to anyone who is interested in taking over. Please also indicate your interest, if you could imagine participating in this part time, in case a number of people would want to share the updating process. And please also keep in mind that this should be a longer time commitment.

However this turns out, it’s been a nice an interesting experiment in all its facets for about a year, and I enjoyed updating it during this time.

best,  Dominik

Stuart Ross Taylor

Research School of Earth Sciences, Australian National University. Canberra, Australia

Recent geochemical and geophysical data from the Moon enable a revision of earlier interpretations regarding lunar origin, structure and bulk composition. Earth and Moon show many similarities among their isotopic compositions, but they have evolved in totally dissimilar ways, probably related to the deficiency of water in the Moon as well as the vast differences in size and internal pressure. Although some global geochemical trends such as volatile depletion based on K/U ratios have been established, current lunar samples come from differentiated regions, making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities although it remains unclear how the latter relate to whole Moon composition. The lack of fractionation effects among the refractory and super-refractory elements indicates that the proto-lunar material seems unlikely to have been vaporized while the depletion of volatile elements may place lower limits on proto-lunar temperatures. The apparent lack of geochemical evidence of an impacting body enables other possible impactors, such as comets, to be considered.

Reference
Taylor SR (in press) The Moon re-examined. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.06.031]
Copyright Elsevier

Link to Article

José C. Aponte^a,b, Jason P. Dworkin^b, Jamie E. Elsila^b

^aNASA Postdoctoral Program at NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
^bNASA Goddard Space Flight Center and Goddard Center for Astrobiology, Greenbelt, Maryland 20771, USA

The study of meteoritic organic compounds provides a unique window into the chemical inventory of the early Solar System and prebiotic chemistry that may have been important for the origin of life on Earth. Multiple families of organic compounds have been extracted from the Murchison meteorite, which is one of the most thoroughly studied carbonaceous chondrites. The amino acids extracted from Murchison have been extensively analyzed, including measurements of non-terrestrial stable isotopic ratios and discoveries of L-enantiomeric excesses for α-dialkyl amino acids, notably isovaline. However, although the isotopic signatures of bulk amine-containing fractions have been measured, the isotopic ratios and enantiomeric composition of individual aliphatic amines, compounds that are chemically related to amino acids, remain unknown. Here, we report a novel method for the extraction, separation, identification and quantitation of aliphatic monoamines extracted from the Murchison meteorite. Our results show a complete suite of structural isomers, with a larger concentration of methylamine and ethylamine and decreasing amine concentrations with increasing carbon number. The carbon isotopic compositions of fourteen meteoritic aliphatic monoamines were measured, with δ¹³C values ranging from +21 to +129‰, showing a decrease in ¹³C with increasing carbon number, a relationship that may be consistent with the chain elongation mechanism under kinetic control previously proposed for meteoritic amino acids. We also found the enantiomeric composition ofsec-butylamine, a structural analog to isovaline, was racemic within error, while the isovaline extracted from the same Murchison piece showed an L-enantiomeric excess of 9.7%; this result suggested that processes leading to enantiomeric excess in the amino acid did not affect the amine. We used these collective data to assess the primordial synthetic origins of these meteoritic aliphatic amines and their potential linkage to meteoritic amino acids.

Reference
Aponte JC, Dworkin JP and Elsila JE (in press) Assessing the origins of aliphatic amines in the murchison meteorite from their compound-specific carbon isotopic ratios and enantiomeric composition. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.06.035]
Copyright Elsevier

Link to Article

Kenji Furuya^1,2 and Yuri Aikawa¹

¹Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan
²Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

We study the influence of the turbulent transport on ice chemistry in protoplanetary disks, focusing on carbon- and nitrogen-bearing molecules. Chemical rate equations are solved with the diffusion term, mimicking the turbulent mixing in the vertical direction. Turbulence can bring ice-coated dust grains from the midplane to the warm irradiated disk surface, and the ice mantles are reprocessed by photoreactions, thermal desorption, and surface reactions. The upward transport decreases the abundance of methanol and ammonia ices at r  30 AU because warm dust temperature prohibits their reformation on grain surfaces. This reprocessing could explain the smaller abundances of carbon and nitrogen bearing molecules in cometary coma than those in low-mass protostellar envelopes. We also show the effect of mixing on the synthesis of complex organic molecules (COMs) in two ways: (1) transport of ices from the midplane to the disk surface and (2) transport of atomic hydrogen from the surface to the midplane. The former enhances the COMs formation in the disk surface, while the latter suppresses it in the midplane. Then, when mixing is strong, COMs are predominantly formed in the disk surface, while their parent molecules are (re)formed in the midplane. This cycle expands the COMs distribution both vertically and radially outward compared with that in the non-turbulent model. We derive the timescale of the sink mechanism by which CO and N2 are converted to less volatile molecules to be depleted from the gas phase and find that the vertical mixing suppresses this mechanism in the inner disks.

Reference
Furuya K and Aikawa Y (2014) Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry. The Astrophysical Journal 790:97.
[doi:10.1088/0004-637X/790/2/97]

Link to Article