¹F. Capaccioni et al. (>10)*
¹Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica (INAF), Rome, Italy.
*Find the extensive, full author and affiliation list on the publishers Website

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ−1), and the broad absorption feature in the 2.9-to-3.6–micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

Reference
Capaccioni F. et al. (2015) The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta. Science 347, 6220
Link to Article [DOI: 10.1126/science.aaa0628]

Reprinted with permission of AAAS

¹Tsubasa Tobase, ¹Akira Yoshiasa, ¹Ling Wang, ¹Hidetomo Hongu, ¹Hiroshi Isobe, ²Ritsuro Miyawaki
¹Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
²Department of Geology and Paleontology, National Museum of Science, 4-1-1, Amakubo, Tsukuba 305-0005, Japan

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Reference
Tobase T, Yoshiasa A, Wang L, Hongu H, Isobe H, Miyawaki R (2015) XAFS study on the Zr local structures in tektites and natural glasses. Journal of Mineralogical and Petrological Sciences (in Press)
Link to Article [http://dx.doi.org/10.2465/jmps.140317]

^1,2Dennis Harries, ³Peter Hoppe ¹Falko Langenhorst
¹Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Carl-Zeiss-Promenade 10, 07745 Jena, Germany
²Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
³Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

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Reference
Harries D, Hoppe P, Langenhorst F (2015) Reactive ammonia in the solar protoplanetary disk and the origin of Earth’s Nitrogen. Nature Geoscience (in Press)
Link to Article [doi:10.1038/ngeo2339]

¹Fara N. Lindsay, ¹Jeremy S. Delaney, ¹Gregory F. Herzog,²Brent D. Turrin, ^1,3Jisun Park, ²Carl C. Swisher III
¹Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, USA
²Department of Earth and Planetary Science, Rutgers University, Piscataway, NJ 08854, USA
³Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058, USA

We report 40Ar/39Ar ages for several lithological components of the brecciated howardite Kapoeta and compare the ages with results for asteroid 4 Vesta as observed by the Dawn mission. Our Kapoeta sample has an unusual, millimeter wide glass vein that intruded into a complex breccia. The plateau ages of three lithic clasts of basaltic composition that were remote from the glass vein range from 4.2 to 4.5 Ga. Such ages are typical of eucritic material; the oldest reflects early magmatic crystallization (∼4.5 Ga∼4.5 Ga), the younger (4.2–4.5 Ga) reflect magmatism associated with protracted cooling. Samples of the glass vein itself, which include relict grains, give apparent ages between 3.1 and 3.9 Ga as do chips from the matrix. We consider both glass and bulk matrix ages as mixing ages; not marking the time of a single event, but dating regolith activity (<3.1–4.1 Ga<3.1–4.1 Ga).
Eight feldspar grains close to the glass vein give markedly younger plateau ages averaging 1.4 Ga. The Ar release spectra for glass vein and breccia subsamples indicate a disturbance in the last 1.4 Ga. Taken together, these younger ages suggest a recent, major thermal event in the history of howardites that has been under-reported – perhaps the impact that formed the Rheasilvia basin on Vesta.

Reference
Lindsay FN, Delaney JS, Herzog GF, Turrin BD, Park J, Swisher III CC (2015) Rheasilvia provenance of the Kapoeta howardite inferred from ∼1 Ga 40Ar/39Ar feldspar Ages. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2014.12.049]

Copyright Elsevier

¹Kathleen E. Vander Kaaden,²Francis M. McCubbin
¹Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM, USA
²Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM, USA

The range in density and compressibility of mercurian melt compositions was determined to better understand the products of a possible mercurian magma ocean and subsequent volcanism. Our experiments indicate that the only mineral to remain buoyant with respect to melts of the mercurian mantle is graphite; consequently, it is the only candidate mineral to have composed a primary floatation crust during a global magma ocean. This exotic result is further supported by Mercury’s volatile-rich nature and inexplicably darkened surface. Additionally, our experiments illustrate that partial melts of the mercurian mantle that compose the secondary crust were buoyant over the entire mantle depth and could have come from as deep as the core-mantle boundary. Furthermore, Mercury could have erupted higher percentages of its partial melts compared to other terrestrial planets because magmas would not have stalled during ascent due to gravitational forces. These findings stem from the FeO-poor composition and shallow depth of Mercury’s mantle, which has resulted in both low melt density and a very limited range in melt density responsible for Mercury’s primary and secondary crusts. The enigmatically darkened, yet low-FeO surface, which is observed today can be explained by secondary volcanism and impact processes that have since mixed the primary and secondary crustal materials.

Reference
Vander Kaaden KE, McCubbin FM (2015) Exotic Crust Formation on Mercury: Consequences of a Shallow, FeO-poor Mantle. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004733]

Published by arrangement with John Wiley&Sons

¹Evelyn Füri, ^1,2Marc Chaussidon, ¹Bernard Marty
¹Centre de Recherches Pétrographiques et Géochimiques, CNRS-UL, 15 rue Notre Dame des Pauvres, BP20, 54501 Vandoeuvre-lès-Nancy, France
²Now at Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, 75005 Paris, France

Nitrogen and noble gas (Ne-Ar) abundances and isotope ratios, determined by CO2 laser extraction static mass spectrometry analysis, as well as Al-Mg and O isotope data from secondary ion mass spectrometry (SIMS) analyses, are reported for a type B calcium-aluminum-rich inclusion (CAI) from the CV3 chondrite NWA 8616. The high (26Al/27Al)i ratio of (5.06 ± 0.50) × 10-5 dates the last melting event of the CAI at View the MathML source39-99+109 ka after the “time zero”, limiting the period during which high-temperature exchanges between the CAI and the nebular gas could have occurred to a very short time interval. Partial isotopic exchange with a 16O-poor reservoir resulted in Δ17O > -5‰ for melilite and anorthite, whereas spinel and Al-Ti-pyroxene retain the inferred original 16O-rich signature of the solar nebula (Δ17O ⩽ -20 ‰). The low 20Ne/22Ne (⩽0.83) and 36Ar/38Ar (⩽0.75) ratios of the CAI rule out the presence of any trapped planetary or solar noble gases. Cosmogenic 21Ne and 38Ar abundances are consistent with a cosmic ray exposure (CRE) age of ∼14 to 20 Ma, assuming CR fluxes similar to modern ones, without any evidence for pre-irradiation of the CAI before incorporation into the meteorite parent body. Strikingly, the CAI contains 1.4 to 3.4 ppm N with a Δ15N value of +8 to +30 ‰. Even after correcting the measured Δ15N values for cosmogenic 15N produced in situ, the CAI is highly enriched in 15N compared to the protosolar nebula (Δ15NPSN = -383 ± 8 ‰; Marty et al., 2011), implying that the CAI-forming region was contaminated by 15N-rich material within the first 0.15 Ma of Solar System history, or, alternatively, that the CAI was ejected into the outer Solar System where it interacted with a 15N-rich reservoir.

Reference
Füri E, Chaussidon M, Marty B (2015) Evidence for an early nitrogen isotopic evolution in the solar nebula from volatile analyses of a CAI from the CV3 chondrite NWA 8616. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.01.004]

Copyright Elsevier

¹Vishnu Reddy et al. (>10)*
¹Planetary Science Institute, 1700 East Fort Lowell Road, Tucson, AZ 85719, USA
*Find the extensive, full author and affiliation list on the publishers Website

We explored the statistical and compositional link between Chelyabinsk meteoroid and potentially hazardous asteroid (86039) 1999 NC43 to investigate their proposed relation proposed by . First, using a slightly more detailed computation we confirm that the orbit of the Chelyabinsk impactor is anomalously close to the asteroid 1999 NC43. We find ∼(1-3) × 10-4 likelihood of that to happen by chance. Taking the standpoint that the Chelyabinsk impactor indeed separated from 1999 NC43 by a cratering or rotational fission event, we run a forward probability calculation, which is an independent statistical test. However, we find this scenario is unlikely at the ∼(10-3 -10-2) level. Secondly, we note that efforts to conclusively prove separation of the Chelyabinsk meteoroid from (86039) 1999 NC43 in the past needs to meet severe criteria: relative velocity ≃1-10 m/s or smaller, and ≃ 100 km distance (i.e. about the Hill sphere distance from the parent body). We conclude that, unless the separation event was an extremely recent event, these criteria present an insurmountable difficulty due to the combination of strong orbital chaoticity, orbit uncertainty and incompleteness of the dynamical model with respect to thermal accelerations. This situation leaves the link of the two bodies unresolved and calls for additional analyses. With that goal, we revisit the presumed compositional link between (86039) 1999 NC43 and the Chelyabinsk body. noted that given its Q-type taxonomic classification, 1999 NC43 may pass this test. However, here we find that while the Q-type classification of 1999 NC43 is accurate, assuming that all Q-types are LL chondrites is not. Our experiment shows that not all ordinary chondrites fall under Q-taxonomic type and not all LL chondrites are Q-types. Spectral curve matching between laboratory spectra of Chelyabinsk and 1999 NC43 spectrum shows that the spectra do not match. Mineralogical analysis of Chelyabinsk (LL chondrite) and (8) Flora (the largest member of the presumed LL chondrite parent family) shows that their olivine and pyroxene chemistries are similar to LL chondrites. Similar analysis of 1999 NC43 shows that its olivine and pyroxene chemistries are more similar to L chondrites than LL chondrites (like Chelyabinsk). Analysis of the spectrum using Modified Gaussian Model (MGM) suggests 1999 NC43 is similar to LL or L chondrite although we suspect this ambiguity is due to lack of temperature and phase angle corrections in the model. While some asteroid pairs show differences in spectral slope, there is no evidence for L and LL chondrite type objects fissioning out from the same parent body. We also took photometric observations of 1999 NC43 over 54 nights during two apparitions (2000, 2014). The lightcurve of 1999 NC43 resembles simulated lightcurves of tumblers in Short-Axis Mode (SAM) with the mean wobbling angle 20°-30°. The very slow rotation of 1999 NC43 could be a result of slow-down by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. While, a mechanism of the non-principal axis rotation excitation is unclear, we can rule out the formation of asteroid in disruption of its parent body as a plausible cause, as it is unlikely that the rotation of an asteroid fragment from catastrophic disruption would be nearly completely halted. Considering all these facts, we find the proposed link between the Chelyabinsk meteoroid and the asteroid 1999 NC43 to be unlikely.

Reference
Reddy V (2015) Link between the potentially hazardous asteroid (86039) 1999 NC43 and the Chelyabinsk meteoroid tenuous. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.006]

Copyright Elsevier

¹Brandon C. Johnson,²David A. Minton,²H. J. Melosh¹Maria T. Zuber
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA

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Reference
Johnson BC, Minton DA, Melosh HJ, Zuber MT (2015) Impact jetting as the origin of chondrules. Nature 517, 339–341

Link to Article [doi:10.1038/nature14105]

^1,2Hiroshi Takeda, ³Hiroshi Nagaoka, ^4,5Akira Yamaguchi, ⁶Yuzuru Karouji, ⁷Yuuki Yazawa
¹Department of Earth and Planetary Science, Graduate School of Sciences, University of Tokyo, Hongo 113-0033, Tokyo, Japan
²Forum Research, Chiba Institute of Technology, Narashino 275-0016, Chiba, Japan
³Research Institute for Science and Engineering, Waseda University, Shinjuku 169-8555, Tokyo, Japan
⁴National Institute of Polar Research, Tachikawa 190-8518, Tokyo, Japan
⁵Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies, Tachikawa 190-8518, Tokyo, Japan
⁶Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Kanagawa, Japan
⁷Department of Life and Environmental Sciences, Chiba Institute of Technology, Narashino 275-0016, Chiba, Japan

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Reference
Takeda H, Nagaoka H, Yamaguchi A, Karouji Y, Yazawa Y (2015) Mineralogy of some evolved LL chondrites with reference to asteroid materials and solar system Evolution. Earth, Planets and Space, 67:5
Link to Article [doi:10.1186/s40623-014-0167-x]

¹Robina Shaheen, ²Paul B. Niles, ^1,3Kenneth Chong, ⁴Catherine M. Corrigan ¹Mark H. Thiemens
¹Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92122;
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058;
³Department of Chemistry, California State Polytechnic University, Pomona, CA 91768; and
⁴Smithsonian Institution, Washington, DC 20004

Carbonate minerals provide critical information for defining atmosphere–hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet’s climate history. Here we report Δ17O, δ18O, and δ13C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere–hydrosphere–geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in 18O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess 17O (0.7‰) that captured the atmosphere–regolith chemical reservoir transfer, as well as CO2, O3, and H2O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in 13C compared with the modern atmosphere.

Reference
Shaheen R, Niles NB, Chong K, Corrigan CM, Thiemens MH (2015) Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere. Proceedings of the National Academy of Sciences 112, 336-341;
Link to Article [doi:10.1073/pnas.1315615112]