¹Rebecca J. Smith, ²Elizabeth B. Rampe, ¹Briony H. N. Horgan, ³Erwin Dehouck
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005612]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN
²NASA/Johnson Space Center, Houston, TX
³Laboratoire de Géologie de Lyon – Terre, Planètes, Environnement, UMR 5276, CNRS, Université Lyon 1, ENS Lyon, Villeurbanne, France
Published by arrangement with John Wiley & Sons

X‐ray amorphous materials have been detected in all samples measured by the CheMin X‐ray diffractometer (XRD) onboard the Mars Science Laboratory rover in Gale Crater, Mars. The origin (s) of these materials are poorly understood, and there are significant uncertainties on their estimated abundances and compositions. Three methods are used to estimate the bulk amorphous component abundance and composition of martian samples using XRD and bulk chemical data: (1) Rietveld refinements, (2) FULLPAT analyses, and (3) mass balance calculations (MBCs). We tested these methods against a quantitative XRD (internal standard) method commonly used in terrestrial laboratories. Additionally, we tested for instrumentation effects by measuring our samples on a laboratory XRD instrument (PANalytical X’Pert Pro) and the CheMin test‐bed instrument (CheMin IV). We used three natural samples known to contain amorphous materials: glacial sediment, Hawaiian soil, and a paleosol. Our methods resulted in nine amorphous abundances and four amorphous compositions for each sample. For a single sample, amorphous abundance estimates and amorphous compositions are relatively similar across all estimation methods. CheMin analog measurements perform well in our tests, with amorphous abundances and compositions comparable to laboratory QXRD measurements, though slightly underestimated. This suggests that previous amorphous component estimates for martian samples are relatively accurate. This study highlights the usefulness of the MBC method for characterizing amorphous materials in terrestrial samples, providing important supplemental information to destructive and time‐consuming size‐separation and dissolution procedures.

^1,2K. Fiege, ²M. Guglielmino, ³N. Altobelli, ²M. Trieloff, ⁴R. Srama, ¹T. M. Orlando
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005564]
¹Georgia Institute of Technology, Atlanta, GA, USA
²Universität Heidelberg, Klaus–Tschira–Labor für Kosmochemie, Institut für Geowissenschaften, Heidelberg, Germany
³ESA, European Space Agency, Madrid, Spain
⁴Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
Published by arrangement with John Wiley & Sons

The role of micrometeorite bombardment in space weathering on asteroid surfaces was studied using a 2 MV Van–De–Graaff accelerator. About 90000–100000 micron– to sub–micron sized copper particles with a mass– and velocity distribution similar to the interplanetary dust population, were fired onto the surfaces of polished Allende CV3 chondrite and eucrite NWA 6966 samples at speeds between km s−1. We find a clear relationship between micro–particle bombardment, infrared reflectance decrease, and overall spectral reddening. Differences in impact effects due to variable particle speed, size and structure are observed. Some Cu–particles form large clusters that break up upon impact and disperse. Other impactors leave imprints on the surface, implant or generate typical craters with rims and spallation features. Very small, fast particles generate small craters without spallation or significant crater rim. Mid–IR–spectra (bulk– and microscopic measurements of individual components), 3D–Laser microscopic images and XRD–spectra from the processed and unprocessed samples were collected. Mid–IR–spectra (700–6000 cm−1) over the entire sample surface, show overall darkening of features. Microscopic IR–spectra show the damage seen as reflectance decrease and spectral reddening, which is variable in the μ–range, depending on impact density and target properties (mineralogic composition). The fine–grained Allende matrix with predominantly Fe–rich olivine seems less affected than coarse–grained chondrules with Mg–rich silicates, where darkening can reach 60%. XRD–analysis also suggests chemical and crystallographical differences in the bombarded sample, due to impact shock.

¹Nicolas Altobelli, ^2,3Katherina Fiege, ⁴Benoit Carry, ³Rachel Soja, ²Massimo Guglielmino, ²Mario Trieloff, ⁵Thomas Michael Orlando, ²Ralf Srama
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005563]
¹ESA, European Space Agency, Madrid, Spain
²Klaus–Tschira–Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Germany
³Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
⁴Université Côte d’ Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
⁵Georgia Institute of Technology, Atlanta, GA, USA
Published by arrangement with John Wiley & Sons

The processes of alteration of airless bodies exposed to the space environment are referred to be as ‘space weathering’. Multiple agents contribute generally to space weathering, to an extent that depends on the specific location of the surface within the Solar System. Typical space weathering agents encountered in the Solar System are: solar radiation, solar wind and cosmic rays, magnetospheric plasma (for example, at Jupiter or Saturn), and cosmic dust. The effect of space weathering is generally assessed by measuring the surfaces optical properties, for example by near‐infrared (IR) spectroscopy. The alteration of the surfaces is due to a cumulative effect over time of all agents. We investigate in this paper the contribution of micro‐meteoroid (dust) bombardment on different asteroids, by using the Micrometeoroid Environment Model (IMEM) for the interplanetary dust populations (IDPs), and a simplified model of Interstellar Dust (ISD) dynamics. We quantify, for different representative asteroids (Main Belt and NEOs), the particle cumulative flux, mass flux, impact velocity and the kinetic impact energy deposited. This work is primarily intended to support laboratory work investigating the effect of energy deposition onto sample surfaces, as well as astronomical observations of optical properties of asteroid surfaces.

¹Pablo Núñez Demarcoa, ²Gonzalo Tancredi, ³Maria Elizabeth Zucolotto, ⁵Loiva Lizia Antonello, ³José María Monzón, ⁴Valentina Pezano, ⁵Amanda Tosi, ¹Caio Villaça
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.09.007]
¹Instituto de Ciencias Geológicas, Facultad de Ciencias, UdelaR, Uruguay
²Departamento de Astronomía, Instituto de Física, Facultad de Ciencias, UdelaR, Uruguay
³LABET/MN/UFRJ, Laboratório Extraterrestre, Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Brazil
⁴Centro Universitario Regional Este, UdelaR, Uruguay
⁵LABSONDA/IGEO/UFRJ, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Brazil

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