¹Adam Culka, ¹Filip Košek, ¹Petr Drahota, ¹Jan Jehlička
¹Charles University in Prague, Institute of Geochemistry, Mineralogy and Mineral Resources, Albertov 6, 12843 Prague, Czech Republic

The presence of sulfates of different hydration states, specifically magnesium sulfates, has been firmly established on Mars from data acquired by both orbital and in-situ measurements. A lander mission typically involves a variety of instruments capable of performing a wide range of experiments from mineralogical tasks to the search for traces of life. It is clear from ongoing research that Raman spectroscopy can cover all of these tasks, and it has already been decided that future mission to Mars will employ a miniature Raman spectrometer. In this paper we report and discuss the Raman spectra of various sulfate minerals, with an emphasis on the magnesium sulfates. These were acquired by a hand-held Raman instrument, using the presently uncommon 532 nm excitation, the wavelength that is planned for the ESA lander mission. A sufficient quality of spectra were obtained with reasonably low spectral acquisition times, and the characteristic shift of the sulfate ν1 band in the MgSO4·n(H2O) minerals was confirmed. This was used for the unambiguous identification of magnesium sulfates of different hydration states. The present testing has confirmed the good performance of the handheld instrumentation for discrimination of structurally similar sulfates of relevance for Mars studies. This step has been proposed as the basis for subsequent testing of this instrumentation under Earth-based but Mars-analogous conditions, even using currently existing miniaturized Raman prototypes.

Reference
Culka A, Košek F, Drahota P, Jehlička J (2014) Use of miniaturized Raman spectrometer for detection of sulfates of different hydration states – significance for Mars studies. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.017]

Copyright Elsevier

¹Alice J. DeSimone, ^1,2Thomas M. Orlando
¹School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400
²School of Physics, Georgia Institute of Technology, Atlanta, GA 30332-0400

H2O (ν = 0) and O(3PJ=2,1,0) desorbates were measured with resonance-enhanced multiphoton ionization following 157-nm irradiation of amorphous solid water (ASW) deposited on a lunar mare basalt. Both H2O photodesorption and O(3PJ) photodissociation products of ASW were studied in the attempt to better understand the competition between photodesorption and photodissociation of water in the condensed phase on a lunar surface. The oxygen atom time-of-flight (TOF) spectrum was measured as a function of spin-orbit state, H2O exposure, and 157-nm irradiation time. Maxwell-Boltzmann distributions with translational temperatures of 10,000 K, 1800 K, 400 K, and 89 K fit the four TOF components. For high H2O exposures, diffusion out of pores in the lunar substrate made a large portion of the O(3PJ) signal appear to be sub-thermal. Water depletion cross sections were measured at exposures between 0.1 and 10 Langmuir (1 L = 10-6 Torr s). These cross sections decreased with increasing coverage and matched previously measured cross sections from a lunar impact melt breccia. Additionally, non-resonant ionization was employed to detect vibrationally excited water indirectly through its fragments. The OH+ fragment of H2O (ν∗) and the O(3PJ) photodissociation product increased in intensity during prolonged irradiation as hydroxyl groups accumulated on the surface and then recombined. For an initial exposure of 5 L H2O, after reaching maximum signal, the cross sections for H2O (ν∗) and O(3P2) depletion were measured to be 1.2 x 10-19 cm2 and 6.7 x 10-20 cm2, respectively.

Reference
DeSimone AJ, Orlando TM (2014) H2O and O(3PJ) Photodesorption from Amorphous Solid Water Deposited on a Lunar Mare Basalt. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.023]

Copyright Elsevier

¹A. Shahar, ¹V.J. Hillgren, ²M.F. Horan, ^1,3J. Mesa-Garcia, c, ¹L.A. Kaufman, ²T.D. Mock
¹Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015, USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015, USA
³Geology Department, Universidad EAFIT, Medellin, Colombia

A series of high pressure and temperature experiments were conducted to better constrain the Fe isotope fractionation during core-mantle differentiation in planetesimal and planetary bodies. Synthetic mixtures of oxides and metal having varying amounts of sulfur, approximating terrestrial and Martian compositions, were melted at 1-2 GPa and 1650°C. Iron isotopic equilibrium between the resulting metal and glass run products was verified for all experiments using the three-isotope technique. Purified Fe from metal and glass was analyzed by multiple-collector ICP-MS in high resolution mode. Iron alloy and silicate glass show a well-resolved Δ57Femetal-silicate of +0.12 ±0.04‰ in a sulfur-free system. Isotope fractionation increases with sulfur content to +0.43 ±0.03‰ at 18 wt.% sulfur in the metal. These results cannot be easily interpreted within the context of known Fe isotope ratios in most natural samples of planetary and asteroidal mantles and therefore suggest more complex processes affected the Fe isotope fractionation therein.

Reference
Shahar A, Hillgren VJ, Horan MF, Mesa-Garcia J, Kaufman LA, Mock TD (2014) Sulfur-controlled iron isotope fractionation experiments of core formation in planetary bodies. Geochimica et Cosmochinica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.08.011]

Copyright Elsevier

¹Raúl O.C. Fonseca,²Guilherme Mallmann, ³Peter Sprung, ¹Johanna E. Sommer, ¹Alexander Heuser, ¹Iris M. Speelmanns, ¹Henrik Blanchard
¹Steinmann-Institut, Universität Bonn, 53115 Bonn, Germany
²School of Earth Sciences, The University of Queensland, Brisbane QLD 4072, Australia
³Institut für Planetologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

The timing of core formation is essential for understanding the early differentiation history of the Earth and the Moon. Because Hf is lithophile and W is siderophile during metal–silicate segregation, the decay of 182Hf to 182W (half-life of 9 Ma) has proven to be a useful chronometer of core–mantle differentiation events. A key parameter for the interpretation of 182Hf/182W data is the Hf/W ratio of the primitive (i.e. undepleted) mantle. Since W is incompatible during mantle melting, its ratio relative to U and other similarly incompatible elements in basalts (e.g. Th, La) may be used as proxies for their mantle sources. However, the assumption that W and U are equally incompatible may be flawed for petrological systems that equilibrated over a large range of oxygen fugacity (fO2). Although W is typically perceived as being homovalent, evidence suggests that U is heterovalent over the range of fO2 inferred for the silicate mantles of the Earth and the Moon.
Here we report new partitioning data for W, U, high-field-strength elements (HFSE), and Th between clinopyroxene, orthopyroxene, olivine, plagioclase and silicate melt. In agreement with previous studies, we show that these elements behave as homovalent elements at fO2 characteristic of Earth’s upper mantle. However, both W and U become more compatible at low fO2, indicating a change in their redox state, with W becoming more compatible at progressively lower fO2. This result for W is particularly unexpected, because this element was thought to be hexavalent even at very low fO2. The much higher compatibility of W4+ (the species inferred here at low fO2) relative to W6+ means that even a small fraction of W4+ will have a significant effect on the overall compatibility of W. Our results imply that over the range of reducing conditions in which lunar differentiation is thought to have taken place (i.e. ∼IW-2 to IW-0.5), W is likely to become fractionated from U. When our partitioning data are applied to model the fractional crystallization of a lunar magma ocean, lunar trends for U/W, Hf/W and Th/W are well reproduced. The result of this model carries with it the implication that the Hf/W of the bulk silicate fractions that comprise the Earth and the Moon are virtually identical.

Reference
Fonseca ROC, Mallmann G, Sprung P, Sommer JE, Heuser A, Speelmanns IM, Blancharda H (2014) Redox controls on tungsten and uranium crystal/silicate melt partitioning and implications for the U/W and Th/W ratio of the lunar mantle. Earth and Planetary Science Letters 404, 1-13.
Link to Article [DOI: 10.1016/j.epsl.2014.07.015]

Copyright Elsevier

¹Senthil Kumar Perumal, ¹J. Prasanna Lakshmi Kopisetti, ¹Krishna Nagula, ¹Rajeev Menon, ¹Sruthi Uppalapati, ²Keerthi Vallabaneni, ²Senthil Kumar Arumugam, ¹Mysaiah Dasari, ¹Seshunarayana, ¹Tangirala, Mrinal K. Sen
¹National Geophysical Research Institute, Council of Scientific & Industrial Research, Hyderabad, India
²National Remote Sensing Centre, Indian Space Research Organization, Hyderabad, India

Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to km-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed and elongated with an average edge angle of 100 degrees. The size distribution of cobble- to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures and faults in the bedrock beneath the crater rim. The fracturing, fragmentation and fluvial degradation of Lonar Crater has important implications for Mars.

Reference
Perumal SK, Kopisetti JPL, Nagula K, Menon R, Uppalapati S, Vallabaneni K, Arumugam SK, Dasari M, Tangirala S, Sen MK (2014) Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt. Journal of Geophysical Research: Planets (in Press)
Link to Article [DOI: 10.1002/2013JE004543]

Published by arrangement with John Wiley&Sons

¹D. Polishook, ^1,2N. Moskovitz, ^1,3F.E. DeMeo, ¹R.P. Binzel
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
³Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

The fission of an asteroid due to fast rotation can expose sub-surface material that was never previously exposed to any space weathering process. We examine the spectral properties of asteroid pairs that were disrupted in the last 2 million years to examine whether the site of the fission can be revealed. We studied the possibility that the sub-surface material, perhaps on one hemisphere, has spectral characteristics differing from the original weathered surface. This was achieved by performing rotationally-resolved spectroscopic observations to look for local variations as the asteroid rotates.
We spectrally observed 11 asteroids in pairs in the near-IR and visible wavelength range. Photometric observations were also conducted to derive the asteroid lightcurves and to determine the rotational phases of the spectral observations. We do not detect any rotational spectral variations within the signal-to-noise of our measurements, which allows us to tightly constrain the extent of any existing surface heterogeneity.
For each observed spectrum of a longitudinal segment of our measured asteroids, we estimate the maximal size of an un-detected “spot” with a spectral signature different than the average. For five asteroids the maximal diameter of such a “spot” is smaller by a factor of two than the diameter of the secondary member of the asteroid. Therefore, the site of the fission is larger than any area with a unique spectral parameters. This means the site of the fission does not have a unique spectrum. In the case of an ordinary chondrite asteroid (S-complex), where the site of fission is expected to present non-weathered spectra, a lack of a fission “spot” (detectable spectroscopically) can be explained if the rotational-fission process is followed by the spread of dust that re-accumulates on the primary asteroid and covers it homogeneously. This is demonstrated for the young asteroid 6070 that presents an Sq-type spectrum while its inner material, that is presumably revealed on the surface of its secondary member, 54827, has a non-weathered, Q-type spectrum. The spread of dust observed in the disintegration event of the asteroid P/2013 R3, might be an example of such a process and an indication that P/2013 R3 was indeed formed in a rotational-fission event.

Reference
Polishook D, Moskovitz FE, DeMeo RP, Binzel RP (2014) Rotationally Resolved Spectroscopy of Asteroid Pairs: No Spectral Variation Suggests Fission is followed by Settling of Dust. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.010]

Copyright Elsevier

¹Patrick Michel, ²Martin Jutzi, ³Derek C. Richardson, ⁴Cyrena A. Goodrich, ⁴William K. Hartmann, ⁴David P. O’Brien
¹Laboratoire Lagrange, Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice, Cedex 4, France
²Physics Institute, Space Research and Planetary Sciences Center for Space and Habitability, University of Bern, Switzerland
³Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁴Planetary Science Institute, 1700 E. Ft. Lowell, Tucson, AZ 85719, USA

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

Reference
Michel P, Jutzi M, Richardson DC, Goodrich CA, Hartmann WK, O’Brien DP (2014) Selective sampling during catastrophic disruption: Mapping the location of reaccumulated fragments in the original parent Body. Planetary and Space Science (in Presss)
Link to Article [DOI: 10.1016/j.pss.2014.08.005]

¹Paul S. Hardersen, ²Vishnu Reddy, ³Rachel Roberts, ⁴Amy Mainzer
¹University of North Dakota, Department of Space Studies, 4149 University Avenue, Stop 9008, 530 Clifford Hall, Grand Forks, North Dakota, USA 58202-9008
²Planetary Science Institute, 1700 E. Fort Lowell Road, Suite 106, Tucson, Arizona, USA 85719
³University of North Dakota, Department of Space Studies, 4149 University Avenue, Stop 9008, 521 Clifford Hall, Grand Forks, North Dakota, USA 58202-9008
⁴Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California, USA 91109

Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta’s collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (). We define ‘genetic Vestoids’ as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid’s major surface mineralogy (). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta.
Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ∼0.7-2.5 μm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite-Eucrite-Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the overall current abundance of basaltic material in the main asteroid belt ().
This work reports high-quality NIR spectra, and their respective interpretations, for eight Vp-type asteroids, as defined by , that were observed at the NASA Infrared Telescope Facility on January 14, 2013 UT. They include: (3867) Shiretoko, (5235) Jean-Loup, (5560) Amytis, (6331) 1992 FZ1, (6976) Kanatsu, (17469) 1991 BT, (29796) 1999 CW77, and (30872) 1992 EM17. All eight asteroids exhibit the broad ∼0.9- and ∼1.9-μm mineral absorption features indicative of pyroxene on each asteroid’s surface. Data reduction and analysis via multiple techniques produced consistent results for the derived spectral absorption band centers and average pyroxene surface chemistries for all eight asteroids (). (3867) Shiretoko is most consistent with the eucrite meteorites while the remaining seven asteroids are most consistent with the howardite meteorites. The existing evidence suggests that all eight of these Vp-type asteroids are genetic Vestoids that probably originated from Vesta’s surface.

Reference
Hardersen PS, Reddy V, Roberts R, Mainzer A (2014) More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.020]

Copyright Elsevier

^1,2Sheridan E. Ackissa, ³J.J. Wray
¹School of Mathematics, Georgia Institute of Technology, Atlanta, GA 30332
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723
³School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332

Hydrated sulfate minerals record the history of water and habitable environments on Mars, yet prior studies of them have neglected a vast region surrounding the planet’s south pole. Some of the few sulfates reported there are localized to putative ancient volcanoes that may have erupted under an ice sheet, possibly forming sulfates via hydrothermal alteration. Alternatively, sulfates may have formed more recently from sunlight causing minor melting of polar ices and the weathering of embedded dust particles, a process thought to explain the sulfates found near Mars’s north pole. To test these hypotheses, we searched for southern high-latitude sulfates using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO), focusing on regions that include putative volcanoes or geologically similar landforms. In 217 targeted images, we used spectral parameters to identify regions of interest from which we extracted spectra. The spectra were then visually compared to laboratory spectra to identify possible hydrated mineral constituents. In this paper, we present spectra from 16 of the images and statistics derived from the full set of 217, along with spectra from one mapping tile. We find that hydrated sulfates are found throughout the southern high latitudes suggesting a ubiquitous process for hydrated mineral formation and/or the relocation of hydrated minerals due to a long history of impacts, aeolian transport, weathering and periglacial processes.

Reference
Ackissa SE, Wray JJ (2014) Occurrences of possible hydrated sulfates in the southern high latitudes of Mars. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.016]

Copyright Elsevier

¹Ottaviano Ruesch et al. (>10)*
¹Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Germany
*Find the extensive, full author and affiliation list on the publishers Website

The magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR/Dawn) orbital observations of Vesta’s surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta’s surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe2+/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (<~50-60 vol%) is found in 2–5 km wide, morphologically fresh areas. Our global survey reveals a dozen of these areas clustering in the eastern hemisphere of Vesta. The hemispherical coincidence with a widespread, low enrichment in diogenite-like pyroxene suggests the presence of a distinct compositional terrain. On the central mound of the Rheasilvia impact basin, no olivine enrichment was found, suggesting the absence of an olivine-dominated mantle above the basin’s excavation depth or, alternatively, a low amount of olivine homogeneously mixed with diogenite-like pyroxenes. Rare olivine-enriched areas in close proximity to diogenite-like pyroxene are found as part of material ejected by the Rheasilvia impact. Such co-occurrence is reminiscent of local, ultramafic lithologies within the crust. The possible formation of such lithologies on Vesta is supported by some HED meteorites dominated by olivine and orthopyroxene.

Reference
Ruesch et al. (2014) Detections and geologic context of local enrichments in olivine on Vesta with VIR/Dawn data. Journal of Geophysical Research: Planets (in Press)
Link to Article [10.1002/2014JE004625]

Published by Arrangement with John Wiley&Sons