Thomas Mueller^a,b,*, E. Bruce Watson^a, Dustin Trail^a,c, Michael Wiedenbeck^d, James Van Orman^e and Erik H. Hauri^f

^aNew York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 8[th] Street, Troy, NY 12180, USA
^bInstitut für Geologie, Mineralogie & Geophysik, Ruhr-Universität Bochum, D-44801 Bochum, Germany
^cDepartment of Earth and Environmental Sciences, University of Rochester, Rochester NY, 14627.
^dHelmholtz Zentrum Potsdam, GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
^eDept. of Earth, Environmental and Planetary Sciences, Case Western University, Cleveland, USA
^fCarnegie Institution of Washington, Washington, DC 20015, USA

Carbon is an abundant element of planets and meteorites whose isotopes provide unique insights into both organic and inorganic geochemical processes. The identities of carbonaceous phases and their textural and isotopic characters shed light on dynamical processes in modern Earth systems and the evolution of the early solar system. In meteorites and their parent bodies, reduced carbon is often associated with Fe-Ni alloys, so knowledge of the mechanisms that fractionate C isotopes in such phases is crucial for deciphering the isotopic record of planetary materials. Here we present the results of a diffusion-couple experiment in which cylinders of polycrystalline Fe containing 11,500 and 150 μg/g of C were juxtaposed at 1273K and 1.5 GPa for a duration of 36 min. Diffusion profiles of total C concentration and ¹³C/¹²C were measured by secondary ion mass spectrometry (SIMS). The elemental diffusivity extracted from the data is ∼3.0 × 10^-11 m²s^-1, where ¹³C/¹²C was observed to change significantly along the diffusion profile, reflecting a higher diffusivity of ¹²C relative to ¹³C. The maximum isotopic fractionation along the diffusion profile is ∼30-40‰. The relative diffusivities (D) of the carbon isotopes can be related to their masses (M) by D_13C/D_12C = (M_12C/M_13C)^β; the exponent β calculated from our data has a value of 0.225±0.025. Similarly high β values for diffusion of other elements in metals have been taken as an indication of interstitial diffusion, so our results are consistent with C diffusion in Fe by an interstitial mechanism. The high β-value reported here means that significant fractionation of carbon isotopes in nature may arise via diffusion in Fe(-Ni) metal, which is an abundant component of planetary interiors and meteorites.

Reference
Mueller T, Watson EB, Trail D, Wiedenbeck M, Orman JV and Hauri EH (in press) Diffusive fractionation of carbon isotopes in γ-Fe: experiment, models and implications for early solar system processes. Geochimica et Cosmochimica Acta
[doi:10.1002/2013JE004426]
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M. H. Jones^1,*, D. Bewsher², D. S. Brown²

¹Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, Buckinghamshire MK7 6AA, UK.
²Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire PR1 2HE, UK.

The gravitational interaction of dust in the zodiacal cloud with individual planets is expected to give rise to ringlike features: Such a circumsolar ring has been observed associated with Earth, but such resonance rings have not been confirmed to exist for other planets. Here, we report on sensitive photometric observations, based on imaging from the STEREO mission, that confirm the existence of a dust ring at the orbit of Venus. The maximum overdensity of dust in this ring, compared to the zodiacal cloud, is ~10%. The radial density profile of this ring differs from the model used to describe Earth’s ring in that it has two distinct steplike components, with one step being interior and the other exterior to the orbit of Venus.

Reference
Jones MH, Bewsher D and Brown DS (2013) Imaging of a Circumsolar Dust Ring Near the Orbit of Venus. Science 342:960-963.
[doi:10.1126/science.1243194]
Reprinted with permission from AAAS

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Samuel P. Kounaves^a, Brandi L. Carrier^a, Glen D. O’Neil^a, Shannon T. Stroble^b, Mark W. Claire^c,d

^aDepartment of Chemistry, Tufts University, Medford, MA, 02155, USA.
^bFranklin Pierce University, Department of Chemistry, Rindge, NH 03461, USA.
^cUniversity of St. Andrews, Department of Earth & Environmental Sciences, St. Andrews, UK.
^dBlue Marble Space Institute of Science, P.O. Box 85561, Seattle, WA 98145, USA.

The results from the Viking mission in the mid 1970’s provided evidence that the martian surface contained oxidants responsible for destroying organic compounds. In 2008 the Phoenix Wet Chemistry Lab (WCL) found perchlorate (ClO₄^–) in three soil samples at concentrations from 0.5 to 0.7 wt%. The detection of chloromethane (CH₃Cl) and dichloromethane (CH₂Cl₂) by the Viking pyrolysis gas chromatograph-mass spectrometer (GC-MS) may have been a result of ClO₄^– at that site oxidizing either terrestrial organic contaminates or, if present, indigenous organics. Recently, the Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity directly measured the presence of CH₃Cl, CH₂Cl₂ and, along with measurements of HCl and oxygen, indirectly indicate the presence of ClO₄^–. However, except for Phoenix, no other direct measurement of the ClO₄^– anion in martian soil or rock has been made. We report here ion chromatographic (IC) and isotopic analyses of a unique sawdust portion of the martian meteorite EETA79001 that show the presence by mass of 0.6 ± 0.1 ppm ClO₄^– , 1.4 ± 0.1ppm ClO₃^–, and 16 ± 0.2 ppm NO₃^– at a quantity and location within the meteorite that is difficult to reconcile with terrestrial contamination. The sawdust sample consists of basaltic material with a minor salt-rich inclusion in a mass ratio of ∼300:1, thus the salts may be 300 times more concentrated within the inclusion than the whole sample. The molar ratios of NO₃^– : ClO₄^– and Cl- : ClO₄^–, are very different for EETA79001 at ∼ 40:1 and 15:1, respectively, than the Antarctic soils and ice near where the meteorite was recovered at ∼ 10,000:1 and 5000:1, respectively. In addition, the isotope ratios for EETA79001 with δ¹⁵N = -10.48 ± 0.32 ‰ and δ¹⁸O = +51.61 ± 0.74 ‰ are significantly different from that of the nearby Miller Range blue ice with δ¹⁵N = +102.80 ± 0.14 ‰ and δ¹⁸O = +43.11 ± 0.64 ‰. This difference is notable, because if the meteorite had been contaminated with nitrate from the blue ice, the δ¹⁵N values should be the same. More importantly, the δ¹⁵N is similar to the uncontaminated Tissint Mars meteorite with δ¹⁵N = -4.5 ‰. These findings suggest a martian origin of the ClO₄^–, ClO₃^– and NO₃^– in EETA79001, and in conjunction with previous discoveries, support the hypothesis that they are present and ubiquitous on Mars. The presence of ClO₃^– in EETA79001 suggests the accompanying presence of other highly oxidizing oxychlorines such as ClO₂^– or ClO^–, produced both by UV oxidation of Cl^– and γ- and x-ray radiolysis of ClO₄^–. Since such intermediary species may contribute to oxidization of organic compounds, only highly refractory and/or well-protected organics are likely to survive. The global presence of ClO₄^–, ClO₃^–, and NO₃^–, has broad implications for the planet-wide water cycle, formation of brines, human habitability, organics, and life.

Reference
Kounaves SP, Carrier BL, O’Neil GD, Stroble ST and Claire MW (in press) Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: implications for oxidants and organics. Icarus
[doi:10.1016/j.icarus.2013.11.012]
Copyright Elsevier

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Jian-Yang Li¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Planetary Science Institute, 1700 E. Ft. Lowell Road, Suite 106, Tucson, AZ 85719, USA

We report results from broadband visible images of comet C/2012 S1 (ISON) obtained with the Hubble Space Telescope Wide Field Camera 3 on 2013 April 10. C/ISON’s coma brightness follows a 1/ρ (where ρ is the projected distance from the nucleus) profile out to 5000 km, consistent with a constant speed dust outflow model. The turnaround distance in the sunward direction suggests that the dust coma is composed of sub-micron-sized particles emitted at speeds of tens of m s^-1. A(θ)fρ, which is commonly used to characterize the dust production rate, was 1340 and 1240 cm in the F606W and F438W filters, respectively, in apertures <1.”6 in radius. The dust colors are slightly redder than solar, with a slope of 5.0% ± 0.2% per 100 nm, increasing to >10% per 100 nm 10,000 km down the tail. The colors are similar to those of comet C/1995 O1 (Hale-Bopp) and other long-period comets, but somewhat bluer than typical values for short-period comets. The spatial color variations are also reminiscent of C/Hale-Bopp. A sunward jet is visible in enhanced images, curving to the north and then tailward in the outer coma. The 1.”6 long jet is centered at a position angle of 291°, with an opening angle of ~45°. The jet morphology remains unchanged over 19 hr of our observations, suggesting that it is near the rotational pole of the nucleus, and implying that the pole points to within 30° of (R.A., decl.) = (330°, 0°). This pole orientation indicates a high obliquity of 50°-80°.

Reference
Li J-Y et al. (2013) Characterizing the Dust Coma of Comet C/2012 S1 (ISON) at 4.15 AU from the Sun. The Astrophysical Journal – Letters 342:960-963.
[doi:10.1088/2041-8205/779/1/L3]

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