¹W.H. Farrand, ²T.D. Glotch, ³B. Horgan

¹Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO, 80301
²Department of Geosciences, Stony Brook University, Stony Brook, NY, 11794
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, W. Lafayette, IN, 47907

The Mawrth Vallis region on Mars is associated with extensive layered deposits containing a stratigraphic sequence of Fe/Mg smectites overlain by Al phyllosilicates. Earlier studies have reported restricted exposures of the ferric sulfate mineral jarosite on top of the sequence. In this paper we have used CRISM data covering the northern portion of the Mawrth Vallis region to find a new jarosite exposure and multiple occurrences of the mixed valence Fe-sulfate mineral copiapite (Fe²⁺Fe³⁺₄(SO₄)₆(OH)₂⋅ 20(H₂O)). HiRISE imagery indicate that the copiapite exposures lie on top of the Al phyllosilicates and thus post-date that unit either as a coating or as extensive veins. The presumed copiapite exposures are associated with high values of a “SINDX” parameter derived from CRISM data. Application of several spectral matching metrics over a spectral subsection indicated several candidates for the high SINDX phase including copiapite, ferricopiapite and metavoltine (another mixed valence Fe-sulfate mineral). Visible and near infrared CRISM spectra of the high SINDX areas are most consistent with the phase being copiapite. On Earth copiapite generally occurs as efflorescent coatings in acid mine drainage environments or in association with acid sulfate soils. The presence of jarosite and copiapite indicates the presence of acidic waters. Such acid waters could have contributed to the formation of the underlying Al phyllosilicate minerals. A possible mode of origin for these minerals in this region would involve a fluctuating ground water table and the weathering of Fe sulfide minerals.

Reference

Farrand WH, Glotch TD, Horgan B (2014) Detection of Copiapite in the northern Mawrth Vallis Region of Mars: Evidence of acid sulfate Alteration. Icarus, in Press

Link to Article: [DOI: 10.1016/j.icarus.2014.07.003]

Copyright Elsevier

Lindsay P Keller¹ and Eve L Berger²

¹Robert M Walker Laboratory for Space Science, Code KR, Astromaterials
Research and Exploration Science, NASA Johnson Space Center, Houston, TX
77058, USA
²GeoControl Systems, Inc. – Jacobs JETS contract – NASA Johnson Space
Center, Houston, TX 77058, USA

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Reference

Keller LP, Berger EL (2014) A transmission electron microscope study of Itokawa regolith grains. Earth, Planets and Space 66, 71

Link to Article [doi:10.1186/1880-5981-66-71]

José M Madied¹

¹Facultad de Ciencias Experimentales, Universidad de Huelva, Huelva 21071, Spain

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

Reference

Madied JM (2014) Robotic systems for the determination of the composition of solar system materials by means of fireball spectroscopy. Earth, Planets and Space 66, 70

Link to Article [doi:10.1186/1880-5981-66-70]

M.Nachon¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Laboratoire de Planétologie et Géodynamique de Nantes, CNRS, UMR6112, Université de Nantes, Nantes, France

The Curiosity rover has analyzed abundant light-toned fracture-fill material within the Yellowknife Bay sedimentary deposits. The ChemCam instrument, coupled with Mastcam and ChemCam/Remote Micro Imager images, was able to demonstrate that these fracture fills consist of calcium sulfate veins, many of which appear to be hydrated at a level expected for gypsum and bassanite. Anhydrite is locally present, and is found in a location characterized by a nodular texture. An intricate assemblage of veins crosses the sediments, which were likely formed by precipitation from fluids circulating through fractures. The presence of veins throughout the entire ~5 m thick Yellowknife Bay sediments suggests that this process occurred well after sedimentation and cementation/lithification of those sediments. The sulfur-rich fluids may have originated in previously precipitated sulfate-rich layers, either before the deposition of the Sheepbed mudstones, or from unrelated units such as the sulfates at the base of Mount Sharp. The occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively non-acidic conditions.

Reference

Nachon M, Clegg SM, Mangold N, Schröder S, Kah LC, Dromart G, Ollila A, Johnson JR, Oehler DZ, Bridges JC et al. (Accepted) Calcium sulfate veins characterized by ChemCam/Curiosity at Gale Crater, Mars
Journal of Geophysical Research: Planets 2169-9100

Link to Article [DOI: 10.1002/2013JE004588]

Published by arrangement with John Wiley & Sons

T.C. Prissel, S.W. Parman, C.R.M. Jackson, M.J. Rutherford, P.C. Hess, J.W. Head, L. Cheek, D. Dhingra, C.M. Pieters

Department of Earth, Environmental & Planetary Sciences, Brown University, Providence, RI 02912, USA

NASA’s Moon Mineralogy Mapper (M³) has identified and characterized a new lunar rock type termed pink spinel anorthosite (PSA) (Pieters et al., 2011). Dominated by anorthitic feldspar and rich in MgAl₂O₄ spinel, PSA appears to have an unusually low modal abundance of mafic silicates, distinguishing it from known lunar spinel-bearing samples. The interaction between basaltic melts and the lunar crust and/or assimilation of anorthitic plagioclase have been proposed as a possible mechanism for PSA formation (Gross and Treiman, 2011 and Prissel et al., 2012). To test these hypotheses, we have performed laboratory experiments exploring magma–wallrock interactions within the lunar crust. Lunar basaltic melts were reacted with anorthite at 1400 °C and pressures between 0.05–1.05 GPa. Results indicate that PSA spinel compositions are best explained via the interaction between Mg-suite parental melts and anorthositic crust. Mare basalts and picritic lunar glasses produce spinels too rich in Fe and Cr to be consistent with the M³ observations.
The experiments suggest that PSA represents a new member of the plutonic Mg-suite. If true, PSA can be used as a proxy for spectrally identifying areas of Mg-suite magmatism on the Moon. Moreover, the presence of PSA on both the lunar nearside and farside (Pieters et al., in press) indicates Mg-suite magmatism may have occurred on a global scale. In turn, this implies that KREEP is not required for Mg-suite petrogenesis (as KREEP is constrained to the nearside of the Moon) and is only necessary to explain the chemical make-up of nearside Mg-suite samples.

Reference
Prissel TC, Parman SW, Jackson CRM, Rutherford MJ, Hess PC, Head JW, Cheek L, Dhingra D and Pieters CM (in press) Pink Moon: The petrogenesis of pink spinel anorthosites and implications concerning Mg-suite magmatism. Earth and Planetary Science Letters 403:144.
[doi:10.1016/j.epsl.2014.06.027]
Copyright Elsevier

Link to Article

Alexander Hubbard

Department of Astrophysics, American Museum of Natural History, New York, NY 10024-5192, USA

In protoplanetary disks, dust grains rich in metallic iron can attract each other magnetically. If they are magnetized to values near saturation, the magnetically induced collision speeds are high enough to knock off the non-magnetized, loosely bound silicates. This process enriches the surviving portions of the dust grains in metallic iron, which further enhances the magnetically mediated collisions. The magnetic enhancement to the collisional cross-section between the iron rich dust results in rapid grain growth leading to planetesimal formation. While this process of knocking off silicates, which we term “magnetic erosion”, occurs only in a very limited portion of a protoplanetary disk, it is a possible explanation for Mercury’s disproportionately large iron core.

Reference
Hubbard A (in press) Explaining Mercury’s Density through Magnetic Erosion. Icarus
[doi:10.1016/j.icarus.2014.06.032]
Copyright Elsevier

Link to Article

Harold Clenet^a, Martin Jutzi^b, Jean-Alix Barrat^c, Erik I. Asphaug^c, Willy Benz^b and Philippe Gillet^a

^aEPSL, Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
^bPhysics Institute, Space Research and Planetary Sciences, Center for Space and Habitability, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
^cUniversité de Bretagne Occidentale, Institut Universitaire Européen de la Mer, CNRS UMR 6538, Place Nicolas Copernic, 29280 Plouzané, France
^dSchool of Earth and Space Exploration, Arizona State University, PO Box 876004, Tempe, Arizona 85287, USA

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

Reference
Clenet H, Jutzi M, Barrat J-A, Asphaug EI, Benz W and Gillet P (2014) A deep crust–mantle boundary in the asteroid 4 Vesta. Nature 511:303.
[doi:10.1038/nature13499]

Link to Article

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]

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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

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