Christa Gall^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aDepartment of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark

We currently do not have a copyright agreement with this publisher and cannot display the abstract here.

Reference
Gall et al. (2014) Rapid formation of large dust grains in the luminous supernova 2010jl. Nature 511:326.
[doi:10.1038/nature13558]

Link to Article

Michael Schäfer^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aMax Planck Institute for Solar System Research, 37077 Göttingen, Germany

We produced two 1:250,000 scale geologic maps of the adjacent quadrangles Av-6 Gegania and Av-7 Lucaria, located in the equatorial region of (4) Vesta (0° E – 144° E, 22° S – 22° N). The mapping is based on clear and color filter images of the Framing Camera (FC) onboard the Dawn spacecraft, which has captured the entire illuminated surface of Vesta with high spatial resolution (up to ∼20 m/pixel), and on a digital terrain model derived from FC imagery. Besides the geologic mapping itself, a secondary purpose of this work is to investigate one of the most prominent morphological features on Vesta, namely the aggregation of several giant equatorial troughs termed the Divalia Fossae, most probably formed during the Rheasilvia impact near Vesta’s south pole. The up to 465 km long and 22 km wide troughs show height differences of up to 5 km between adjacent troughs and ridges. Another imprint of the Rheasilvia impact is the >350 km long and ∼250 km wide swath of ejecta crossing quadrangle Av-6 Gegania. This lobe shows a distinct appearance in FC color ratios and a high albedo in FC images, indicating a mineralogical similarity to material typically found within the Rheasilvia basin, in particular composed of diogenite-rich howardites. Almost the entire northern half of the mapping area shows the oldest surface, being dominated by upper crustal basaltic material. To the south, increasingly younger formations related to the Rheasilvia impact occur, either indicated by the troughs formed by Rheasilvia or by the Rheasilvia ejecta itself. Only medium sized impact craters with diameters less than 22 km occur within the two mapped quadrangles. Some of the craters exhibit ejecta blankets and/or distinctly dark or bright ejecta material in ejecta rays outside and exposures within the crater, and mass-wasting deposits down crater slopes, forming the youngest surfaces.

Reference
Schäfer et al. (in press) Imprint of the Rheasilvia Impact on Vesta – Geologic Mapping of Quadrangles Gegania and Lucaria. Icarus
[doi:10.1016/j.icarus.2014.06.026]
Copyright Elsevier

Link to Article

M. P. Ronco and G. C. de Elía

Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata and Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP, Paseo del Bosque S/N, 1900 La Plata, Argentina

Context. Several studies, observational and theoretical, suggest that planetary systems with only rocky planets are the most common in the Universe.
Aims. We study the diversity of planetary systems that might form around Sun-like stars in low-mass disks without gas-giant planets. We focus especially on the formation process of terrestrial planets in the habitable zone (HZ) and analyze their water contents with the goal to determine systems of astrobiological interest. In addition, we study the formation of planets on wide orbits because they can be detected with the microlensing technique.
Methods. N-body simulations of high resolution were developed for a wide range of surface density profiles. A bimodal distribution of planetesimals and planetary embryos with different physical and orbital configurations was used to simulate the planetary accretion process. The surface density profile combines a power law for the inside of the disk of the form r^−γ, with an exponential decay to the outside. We performed simulations adopting a disk of 0.03 M_⊙ and values of γ = 0.5, 1 and 1.5.
Results. All our simulations form planets in the HZ with different masses and final water contents depending on the three different profiles. For γ = 0.5, our simulations produce three planets in the HZ with masses ranging from 0.03 M_⊕ to 0.1 M_⊕ and water contents between 0.2 and 16 Earth oceans (1 Earth ocean =2.8 × 10^-4 M_⊕). For γ = 1, three planets form in the HZ with masses between 0.18 M_⊕ and 0.52 M_⊕ and water contents from 34 to 167 Earth oceans. Finally, for γ = 1.5, we find four planets in the HZ with masses ranging from 0.66 M_⊕ to 2.21 M_⊕ and water contents between 192 and 2326 Earth oceans. This profile shows distinctive results because it is the only one of those studied here that leads to the formation of water worlds.
Conclusions. Since planetary systems with γ = 1 and 1.5 present planets in the HZ with suitable masses to retain a long-lived atmosphere and to maintain plate tectonics, they seem to be the most promising candidates to be potentially habitable. Particularly, these systems form Earths and Super-Earths of at least 3 M_⊕ around the snow line, which can be discovered by the microlensing technique.

Reference
Ronco  MP and de Elía GC (2014) Diversity of planetary systems in low-mass disks:Terrestrial-type planet formation and water delivery. Astronomy & Astrophysics 567:A54.
[doi:10.1051/0004-6361/201323313]
Reproduced with permission © ESO

Link to Article

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