Oxygen isotopic ratios of primordial water in carbonaceous chondrites

1Wataru Fujiya
Earth and Planetary Science Letters 481, 264-272 Link to Article [https://doi.org/10.1016/j.epsl.2017.10.046]
1Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
Copyright Elsevier

In this work, I estimate the δ18O and δ17O values of primordial water in CM chondrites to be 55 ± 13 and 35 ± 9‰, respectively, based on whole-rock O and H data. Also, I found that the O and/or H data of Antarctic meteorites are biased, which is attributed to terrestrial weathering. This characteristic O isotopic ratio of water together with corresponding water abundances in CM chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula, where mass-independent O isotopic fractionation and water destruction may have occurred. Another possible mechanism to produce the inferred O isotopic ratio of water would be O isotopic fractionation between water vapor and ice, which likely occurred near the condensation front of H2O (snow line) in the solar nebula. The inferred O isotopic ratio of water suggests that carbonate in CM chondrites formed at low temperatures of <150 °C. The O isotopic ratios of primordial water in chondrites other than CM chondrites are not well constrained.

Origin and abundance of water in carbonaceous asteroids

1Yves Marrocchi, 1David V. Bekaert, 1Laurette Piani
Earth and Planetary Science Letetrs 482, 23-32 Link to Article [https://doi.org/10.1016/j.epsl.2017.10.060]
1CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-les-Nancy, F-54501, France
Copyright Elsevier

The origin and abundance of water accreted by carbonaceous asteroids remains underconstrained, but would provide important information on the dynamic of the protoplanetary disk. Here we report the in situ oxygen isotopic compositions of aqueously formed fayalite grains in the Kaba and Mokoia CV chondrites. CV chondrite bulk, matrix and fayalite O-isotopic compositions define the mass-independent continuous trend (δ17O = 0.84 ± 0.03 × δ18O − 4.25 ± 0.1), which shows that the main process controlling the O-isotopic composition of the CV chondrite parent body is related to isotopic exchange between 16O-rich anhydrous silicates and 17O- and 18O-rich fluid. Similar isotopic behaviors observed in CM, CR and CO chondrites demonstrate the ubiquitous nature of O-isotopic exchange as the main physical process in establishing the O-isotopic features of carbonaceous chondrites, regardless of their alteration degree. Based on these results, we developed a new approach to estimate the abundance of water accreted by carbonaceous chondrites (quantified by the water/rock ratio) with CM (0.3–0.4) ≥ CR (0.1–0.4) ≥ CV (0.1–0.2) > CO (0.01–0.10). The low water/rock ratios and the O-isotopic characteristics of secondary minerals in carbonaceous chondrites indicate they (i) formed in the main asteroid belt and (ii) accreted a locally derived (inner Solar System) water formed near the snowline by condensation from the gas phase. Such results imply low influx of D- and 17O- and 18O-rich water ice grains from the outer part of the Solar System. The latter is likely due to the presence of a Jupiter-induced gap in the protoplanetary disk that limited the inward drift of outer Solar System material at the exception of particles with size lower than 150 μm such as presolar grains. Among carbonaceous chondrites, CV chondrites show O-isotopic features suggesting potential contribution of 17–18O-rich water that may be related to their older accretion relative to other hydrated carbonaceous chondrites.

Laboratory mid-IR spectra of equilibrated and igneous meteorites. Searching for observables of planetesimal debris

1,2,3B.L.de Vries,4H.Skogby, 5,6L.B.F.M.Waters, 5,6M.Min
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.10.029]
1Stockholm University Astrobiology Centre, Stockholm SE-106 91, Sweden
2AlbaNova University Centre, Stockholm University, Department of Astronomy, Stockholm SE-106 91, Sweden
3Scientific Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, Noordwijk 2201 AZ, The Netherlands
4Department of Geosciences, Swedish Museum of Natural History, Box 50007, Stockholm SE-104 05, Sweden
5SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
6Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
Copyright Elsevier

Meteorites contain minerals from Solar System asteroids with different properties (like size, presence of water, core formation). We provide new mid-IR transmission spectra of powdered meteorites to obtain templates of how mid-IR spectra of asteroidal debris would look like. This is essential for interpreting mid-IR spectra of past and future space observatories, like the James Webb Space Telescope. First we present new transmission spectra of powdered ordinary chondrite, pallasite and HED meteorites and then we combine them with already available transmission spectra of chondrites in the literature, giving a total set of 64 transmission spectra. In detail we study the spectral features of minerals in these spectra to obtain measurables used to spectroscopically distinguish between meteorite groups. Being able to differentiate between dust from different meteorite types means we can probe properties of parent bodies, like their size, if they were wet or dry and if they are differentiated (core formation) or not.

We show that the transmission spectra of wet and dry chondrites, carbonaceous and ordinary chondrites and achondrite and chondrite meteorites are distinctly different in a way one can distinguish in astronomical mid-IR spectra. Carbonaceous chondrites type < 3 (aqueously altered) show distinct features of hydrated silicates (hydrosilicates) compared to the olivine and pyroxene rich ordinary chondrites (dry and equilibrated meteorites). Also the iron concentration of the olivine in carbonaceous chondrites differs from ordinary chondrites, which can be probed by the wavelength peak position of the olivine spectral features. The transmission spectra of chondrites (not differentiated) are also strongly different from the achondrite HED meteorites (meteorites from differentiated bodies like 4 Vesta), where the latter show much stronger pyroxene signatures.

The two observables that spectroscopically separate the different meteorites groups (and thus the different types of parent bodies) are the pyroxene-olivine feature strength ratio and the peak shift of the olivine spectral features due to an increase in the iron concentration of the olivine.

Characterization of terrestrial hydrothermal alteration products with Mars analog instrumentation: Implications for current and future rover investigations

1,2Sarah R. Black, 1,2Brian M.Hynek
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.10.032]
1Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 1234 Innovation Drive, Boulder, CO 80303, United States
2Department of Geological Sciences, University of Colorado Boulder, Campus Box 600 UCB, Boulder, CO 80303, United States
Copyright Elsevier

Interpretation of Martian geology relies heavily on our understanding of terrestrial analog deposits and our ability to obtain comprehensive and accurate mineralogical compositions. Many previous studies of terrestrial hydrothermal deposits relied on limited datasets and/or did not use instruments analogous to those deployed on Mars. We analyzed 100 hydrothermally altered basalts from Costa Rica, Nicaragua, and Iceland with Mars analog Visible to Short Wave Infrared (VSWIR) spectroscopy, X-ray Diffraction (XRD), and Raman laser spectrometry. Alteration mineralogy consisted of amorphous and crystalline SiO2 (cristobalite, tridymite, quartz), Ca/Al/Fe/Mg-sulfates (gypsum, anhydrite, alunite, jarosite, hexahydrite, alunogen), Fe-, Ti-, and Mg-oxides/hydroxides (hematite, goethite, anatase/brookite, brucite), elemental sulfur, and phyllosilicates (montmorillonite, kaolinite). Results indicate VSWIR is best suited for identification of X-ray amorphous materials such as hydrated SiO2 and phyllosilicates, while XRD is best utilized for highly ordered crystalline materials such as sulfates, crystalline SiO2 polymorphs, elemental sulfur, and Mg-hydroxides identification. Surprisingly, XRD had the lowest identification rates for Fe-oxides/hydroxides (42% compared to 61% and 75% for VNIR and Raman, respectively), and nearly equal identification rates as VSWIR for kaolinite (76% for VSWIR, 71% for XRD). Identification of phyllosilicates in XRD, while possible, is not as effective as VSWIR without extensive sample preparation. Our observed identification rates may be attributed to the relative abundance of materials—Fe-oxides/hydroxides being present as surface coatings, the presence of large amounts of kaolinite in some samples, and an increased particle size for kaolinite relative to other clays. Elemental sulfur and Fe- and Ti-oxides/hydroxides were more readily identified with Raman. With NASA’s current focus on habitability, hydrothermally altered areas—which we know to host a wide range of microbial life here on Earth—are of high interest and it is likely that future rovers will encounter similar mineral assemblages. Therefore, future rovers would benefit from using a combination of these methods and expanding the VSWIR sampling range to the full 300–2500 nm to conduct a comprehensive mineralogical investigation.

Mineralogical mapping of Coniraya quadrangle of the dwarf planet Ceres

1A.Raponi et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.10.023]
1INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
Copyright Elsevier

Ceres has been explored by NASA/Dawn spacecraft, which allowed for the discovery of the main mineralogical and compositional characteristics of Ceres’ surface. Here, we use mainly data from the Visible and InfraRed imaging spectrometer (VIR) in order to investigate the main spectral characteristics of the quadrangle Ac-H-2 Coniraya, one of the 15 quads in which Ceres’ surface has been divided. Coniraya quadrangle is characterized by the presence of mostly highly degraded impact craters of diameters between 50 and 200 km and clusters of small to midsize impact craters. Although the composition over the quadrangle appears to be quite uniform, significant differences have been detected between different craters by spectral parameters analysis and spectral modeling. Ernutet crater presents two regions with very peculiar band at 3.4 µm, typical of organics aliphatic material. One region result to be correlated with larger amount of carbonates, the other region does not present such correlation. Ikapati crater shows strong absorption bands at 4.0 µm, indicating the presence of Na-carbonates in the floor and ejecta. Ikapati, Gaue and other craters present smaller spectral features of NH4 and/or OH stretching, suggesting a volatile depletion process induced by the heating of the impact event.

Compositional studies of Mare Moscoviense: New perspectives from Chandrayaan-1 VIS-NIR data

1Megha Bhatt, 2Christian Wöhler, 3Deepak Dhingra, 4Guneshwar Thangjam, 2Daniela Rommel, 4Urs Mall, 5Anil Bhardwaj, 2Arne Grumpe
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.10.009]
1Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, Kerala, India
2Image Analysis Group, Dortmund University of Technology, Otto-Hahn Str. 4, Dortmund 44227, Germany
3Department of Physics, University of Idaho, 875 Perimeter Dr MS 0903, Moscow, ID 83843, USA
4Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, Göttingen 37077, Germany
5Physical Research Laboratory, Ahmedabad 380009, Gujarat, India
Copyright Elsevier

Moscoviense is one of the prominent mare-filled basin on the lunar far side holding key insights about volcanic activity on the far side. Here, we present spectral and elemental maps of mare Moscoviense, using the Moon Mineralogy Mapper (M3) and Infrared Spectrometer-2 (SIR-2) data-sets. The different mare units are mapped based on their spectral properties analyzing both quantitatively (band center, band depth) and qualitatively (Integrated Band Depth composite images), and also using their elemental compositions. We find a total of five distinct spectral units from the basin floor based on the spectral properties. Our analysis suggests that the northern part which was mapped as Iltm unit (Imbrian low Ti, low Fe) by earlier researchers is actually a distinct unit, which is different in composition and age, named as Ivltm unit (Imbrian very low Ti and very low Fe). We obtain the absolute model age of 3.2 Ga with uncertainties of +0.2/−0.5 Ga for the unit Ivltm. The newly identified basalt unit Ivltm is compositionally intermediate to the units Im and Iltm in FeO and TiO2 abundances. We find a total of five distinct spectral units from the basin floor based on the spectral properties. The units Im (Imbrian very low Ti) from southern and northern regions of the basin floor are spectrally distinct in terms of band center position and corresponding band depths but considered a single unit based on the elemental abundance analysis. The units Ivltm and Im are consistent with a high-Al basalt composition. Our detailed analysis of the entire Moscoviense basin indicates that the concentrations of orthopyroxene, olivine, and Mg-rich spinel, named as OOS rock family are widespread and dominant at the western and southern side of the middle ring of the basin with one isolated area found on the northern side of the peak ring.

Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-µm sized cosmochemical analogues

1B.Rosseau et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.10.015]
1LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
Copyright Elsevier

Laboratory spectral measurements of relevant analogue materials were performed in the framework of the Rosetta mission in order to explain the surface spectral properties of comet 67P. Fine powders of coal, iron sulphides, silicates and their mixtures were prepared and their spectra measured in the Vis-IR range. These spectra are compared to a reference spectrum of 67P nucleus obtained with the VIRTIS/Rosetta instrument up to 2.7 µm, excluding the organics band centred at 3.2 µm. The species used are known to be chemical analogues for cometary materials which could be present at the surface of 67P. Grain sizes of the powders range from tens of nanometres to hundreds of micrometres. Some of the mixtures studied here actually reach the very low reflectance level observed by VIRTIS on 67P. The best match is provided by a mixture of sub-micron coal, pyrrhotite, and silicates. Grain sizes are in agreement with the sizes of the dust particles detected by the GIADA, MIDAS and COSIMA instruments on board Rosetta. The coal used in the experiment is responsible for the spectral slope in the visible and infrared ranges. Pyrrhotite, which is strongly absorbing, is responsible for the low albedo observed in the NIR. The darkest components dominate the spectra, especially within intimate mixtures. Depending on sample preparation, pyrrhotite can coat the coal and silicate aggregates. Such coating effects can affect the spectra as much as particle size. In contrast, silicates seem to play a minor role.