Frans J. M. Rietmeijer^1,*, Joseph A. Nuth², Aurora Pun¹

¹Department of Earth and Planetary Sciences, 1-University of New Mexico, Albuquerque, New Mexico, USA
²Astrochemistry Laboratory, Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

This thermal annealing experiment at 1000 K for up to 167 h used a physical mixture of vapor phase-condensed magnesiosilica grains and metallic iron nanograins to test the hypothesis that a mixture of magnesiosilica grains and an Fe-source would lead to the formation of ferromagnesiosilica grains. This exploratory study found that coagulation and thermal annealing of amorphous magnesiosilica and metallic grains yielded ferromagnesiosilica grains with the Fe/(Fe + Mg) ratios in interplanetary dust particles. Furthermore, decomposition of brucite present in the condensed magnesiosilica grains was the source for water and the cause of different iron oxidation states, and the formation of amorphous Fe³⁺-ferrosilica, amorphous Fe³⁺-Mg, Fe-silicates, and magnesioferrite during thermal annealing. Fayalite and ferrosilite that formed from silica/FeO melts reacted with forsterite and enstatite to form Mg, Fe-silicates. The presence of iron in different oxidation states in extraterrestrial materials almost certainly requires active asteroid-like parent bodies. If so, the possible presence of trivalent Fe compounds in comet P/Halley suggests that Halley-type comets are a mixture of preserved presolar and processed solar nebula dust. The results from this thermal annealing experiment further suggest that the Fe-silicates detected in the impact-induced ejecta from comet 9P/Temple 1 might be of secondary origin and related to the impact experiment or to processing in a regolith.

Reference
Rietmeijer FJM, Nuth JA and Pun A (in press) The formation of Mg,Fe-silicates by reactions between amorphous magnesiosilica smoke particles and metallic iron nanograins with implications for comet silicate origins. Meteoritics & Planetary Science
[doi:10.1111/maps.12194]
Published by arrangement with John Wiley & Sons

Link to Article

C.S. Edwards^a,*, J.L. Bandfield^b, P.R. Christensen^c and A.D. Rogers^d

^aCalifornia Institute of Technology, Division of Geological and Planetary Sciences, 1200 E. California Blvd., MC 150-21, Pasadena, CA, 91125
^bSpace Science Institute, 4750 Walnut St., Boulder, Co, 80301
^cArizona State University, School of Earth and Space Exploration, Mars Space Flight Facility, PO BOX 876305, Tempe, AZ, 85287-6305
^dDepartment of Geosciences, Stony Brook University, 255 Earth and Space Sciences, Stony Brook, NY 11794-2100

Flat-floored craters have long been recognized on Mars with early work hypothesizing a sedimentary origin. More recently, high-resolution thermal inertia measurements show that these craters contain some of the rockiest materials on the planet, inconsistent with poorly consolidated sedimentary materials. In this study, the distribution, physical properties (morphology and thermal inertia), and composition of these craters are thoroughly investigated over the entire planet. The majority of the ~2,800 rocky crater floors identified are concentrated in the low albedo (0.1-0.17), cratered southern highlands. These craters were infilled at ~3.5 Ga and are associated with the highest thermal inertia values and some of the most mafic materials identified on the planet. Although several processes may have led to the formation of the crater floors, the most likely scenario is volcanic infilling through fractures created by the impact event. The primitive magma source directly results from decompression melting of the martian mantle by the removal of the crustal material excavated by the impactor. Volcanic infilling of craters by decompression melting appears to only have occurred in early martian history when the lithosphere was still relatively thin and the thermal gradient was high. This process was widespread and responsible for the eruption of significant volumes of primitive material, inside and likely outside of craters. Impact induced decompression melting of the martian mantle accounts for the unusual infilling of martian craters and is a widespread planetary process that has gone previously undocumented.

Reference
Edwards CS, Bandfield JL, Christensen PR and Rogers AD (in press) The formation of infilled craters on mars: evidence for widespread impact induced decompression of the early martian mantle?. Icarus
[doi:10.1016/j.icarus.2013.10.005]
Copyright Elsevier

Link to Article

Justin Filiberto^1,*, Susanne P. Schwenzer^2,3

¹Department of Geology, Southern Illinois University Carbondale, Carbondale, Illinois, USA
²Department of Physical Science, The Open University, Milton Keynes, UK
³Lunar and Planetary Institute, USRA, Houston, Texas, USA

The Mars Exploration Rover Spirit investigated the igneous and alteration mineralogy and chemistry of Home Plate and its surrounding deposits. Here, we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the Home Plate outcrop and surrounding Columbia Hills region in Gusev crater. At high temperatures (300 °C), magnetite occurs at very high W/R ratios, but the alteration assemblage is dominated by chlorite and serpentine over most of the W/R range. Quartz, epidote, and typical high-T phases such as feldspar, pyroxene, and garnet occur at low W/R. At epithermal temperatures (150 °C), hematite occurs at very high W/R. A range of phyllosilicates, including kaolinite, nontronite, chlorite, and serpentine are precipitated at specific W/R. Amphibole, with garnet, feldspar, and pyroxene occur at low W/R. If the CO₂ content of the system is high, the assemblage is dominated by carbonate with increasing amounts of an SiO₂-phase, kaolinite, carpholite, and chlorite with lower W/R. At temperatures of hydrous weathering (13 °C), the oxide phase is goethite, silicates are chlorite, nontronite, and talc, plus an SiO₂-phase. In the presence of CO₂, the mineral assemblage at high W/R remains the same, and only at low W/R, i.e., with increasing salinity, carbonate precipitates. The geochemical gradients observed at Home Plate are attributed to short-lived, initially high (300 °C) temperature, but fast cooling events, which are in agreement with our models and our interpretation of a multistage alteration scenario of Home Plate and Gusev in general. Alteration at various temperatures and during different geological processes within Gusev crater has two effects, both of which increase the habitability of the local environment: precipitation of hydrous sheet silicates, and formation of a brine, which might contain elements essential for life in diluted, easily accessible form.

Reference
Filiberto J and Schwenzer SP (in press) Alteration mineralogy of Home Plate and Columbia Hills—Formation conditions in context to impact, volcanism, and fluvial activity. Meteoritics & Planetary Science
[doi:10.1111/maps.12207]
Published by arrangement with John Wiley & Sons

Link to Article

F. Pauzat¹, Y. Ellinger¹, O. Mousis², M. Ali Dib² and O. Ozgurel¹

¹Laboratoire de Chimie Théorique, UMR 7616-CNRS, UPMC Univ. Paris 06, F-75005 Paris, France
²Institut UTINAM, CNRS/INSU, UMR 6213, Université de Franche-Comté, F-25030 Besançon Cedex, France

We address the problem of the sequestration of Ar, Kr, and Xe by H₃⁺ in the gas-phase conditions encountered during the cooling of protoplanetary disks when H₃⁺ is competing with other species present in the same environment. Using high-level ab initio simulations, we try to quantify other sequestration possibilities involving He, H₃⁺, H₂O, and H₃O⁺ present in the protosolar nebula. Apart from the fact that H₃⁺ complexes formed with heavy noble gases are found to be by far much more stable than those formed with He or H₂O, we show that H₂D⁺ and H₃O⁺, both products of the reactions of H₃⁺ with HD and H₂O, can also be efficient trapping agents for Ar, Kr, and Xe. Meanwhile, the abundance profile of H₃⁺ in the outer part of the nebula is revisited with the use of an evolutionary accretion disk model that allows us to investigate the possibility that heavy noble gases can be sequestered by H₃⁺ at earlier epochs than those corresponding to their trapping in planetesimals. We find that H₃⁺ might be abundant enough in the outer protosolar nebula to trap Xe and Kr prior their condensation epochs, implying that their abundances should be solar in Saturn’s current atmosphere and below the observational limit in Titan. The same scenario predicts that comets formed at high heliocentric distances should also be depleted in Kr and Xe. In situ measurements, such as those planed with the Rosetta mission on 67P/Churyumov-Gerasimenko, will be critical to check the validity of our hypotheses.

Reference
Pauzat F, Ellinger Y, Mousis O, Ali Dib M and Ozgurel O (in press) Gas-phase Sequestration of Noble Gases in the Protosolar Nebula: Possible Consequences on the Outer Solar System Composition. The Astrophysical Journal
[doi:10.1088/0004-637X/777/1/29]

Link to Article

Y. Alibert^1,2, F. Carron¹, A. Fortier¹, S. Pfyffer¹, W. Benz¹, C. Mordasini³ and D. Swoboda¹

¹Physikalisches Institut & Center for Space and Habitability, Universität Bern, 3012 Bern, Switzerland
²Observatoire de Besançon, 41 avenue de l’Observatoire, 25000 Besançon, France
³Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Context. Planet formation models have been developed during the past years to try to reproduce what has been observed of both the solar system and the extrasolar planets. Some of these models have partially succeeded, but they focus on massive planets and, for the sake of simplicity, exclude planets belonging to planetary systems. However, more and more planets are now found in planetary systems. This tendency, which is a result of radial velocity, transit, and direct imaging surveys, seems to be even more pronounced for low-mass planets. These new observations require improving planet formation models, including new physics, and considering the formation of systems.
Aims. In a recent series of papers, we have presented some improvements in the physics of our models, focussing in particular on the internal structure of forming planets, and on the computation of the excitation state of planetesimals and their resulting accretion rate. In this paper, we focus on the concurrent effect of the formation of more than one planet in the same protoplanetary disc and show the effect, in terms of architecture and composition of this multiplicity.
Methods. We used an N-body calculation including collision detection to compute the orbital evolution of a planetary system. Moreover, we describe the effect of competition for accretion of gas and solids, as well as the effect of gravitational interactions between planets.
Results. We show that the masses and semi-major axes of planets are modified by both the effect of competition and gravitational interactions. We also present the effect of the assumed number of forming planets in the same system (a free parameter of the model), as well as the effect of the inclination and eccentricity damping. We find that the fraction of ejected planets increases from nearly 0 to 8% as we change the number of embryos we seed the system with from 2 to 20 planetary embryos. Moreover, our calculations show that, when considering planets more massive than ~5 M_⊕, simulations with 10 or 20 planetary embryos statistically give the same results in terms of mass function and period distribution.

Reference
Alibert Y, Carron F, Fortier A, Pfyffer S, Benz W, Mordasini C and Swoboda D (in press) Theoretical models of planetary system formation: mass vs. semi-major axis. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321690]
Reproduced with permission © ESO

Link to Article

Daniel Clery

We currently seek a copyright agreement with Science to display abstracts of their cosmochemistry related publications.

Reference
Clery D (2013) Impact Theory Gets Whacked. Science  342:183-185.
[doi:10.1126/science.342.6155.183]

Link to Article

J. Farihi^1,*, B. T. Gänsicke², D. Koester³

We currently seek a copyright agreement with Science to display abstracts of their cosmochemistry related publications.

Reference
Farihi J, Gänsicke BT and Koester D (2013) Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet. Science  342:218-220.
[doi:10.1126/science.1239447]

Link to Article

J.A. Barrat^a,*, A. Jambon^b, L. Ferrière^c, C. Bollinger^d, J.A. Langlade^d, C. Liorzou^a, O. Boudouma^b, M. Fialin^b

^aUniversité de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, 29280 Plouzané, France
^bUniversité Pierre et Marie Curie-Paris 6 ISTeP, CNRS UMR 7193, case 110, 4 place Jussieu, 75252 Paris cedex 05, France
^cNatural History Museum, Burgring 7, A-1010 Vienna, Austria
^dCNRS UMS 3113, I.U.E.M., Place Nicolas Copernic, 29280 Plouzané Cedex, France

We report on the major and trace element geochemistry of the impact melts contained in some shergottite meteorites. It has been previously proposed that some of these impact melts formed from a mixture of the host rock and a Martian soil component (e.g., Rao et al., 1999) or from partially weathered portions of the host rock (Chennaoui Aoudjehane et al., 2012). Our results contradict both of these theories. Trace element abundances of a glass pod from the EETA 79001A meteorite are identical to those of the host lithology, and indicate that no additional component is required in this case. The impact melts in Tissint share the same trace element features as the host rock, and no secondary phases produced by Martian secondary processes are involved. The light rare earth enrichments displayed by two small samples of Tissint (Chennaoui Aoudjehane et al., 2012) are possibly the result of some contamination of small stones on desert soil before the recovery of the meteorites.

Reference
Barrat JA, Jambon A, Ferrière L, Bollinger C, Langlade JA, Liorzou C, Boudouma O and Fialin M (in press) No Martian soil component in shergottite meteorites. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.09.033]
Copyright Elsevier

Link to Article

Roger H. Hewins^a,b,*, Brigitte Zanda^a, Hugues Leroux^c, Jean-Alix Barrat^d, Munir Humayun^e, Christa Göpel^f, Richard C. Greenwood^g, Ian A. Franchi^g, Sylvain Pont^a, Jean-Pierre Lorand^h, Cécile Cournèdeⁱ, Jérôme Gattacceca^i,j, Pierre Rochetteⁱ, Maïa Kuga^k, Yves Marrocchi^k, Bernard Marty^k

^aLabo. de Minéralogie et Cosmochimie du Muséum, MNHN and CNRS UMR 7202, 75005 Paris, France
^bDept. of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
^cUnité Matériaux et Transformations, Université Lille 1 and CNRS, UMR8207, F-59655 Villeneuve d’Ascq, France
^dUniversité Européenne de Bretagne and CNRS UMR 6538, U.B.O-I.U.E.M., 29280 Plouzané Cedex, France
^eDept. of Earth, Ocean and Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
^fInstitut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France
^gPSS, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
^hLaboratoire de Planétologie et Géodynamique LPG Nantes – UMR CNRS 6112, 44322 Nantes Cedex 3, France
ⁱCNRS/Aix-Marseille Université, CEREGE UM34, 13545 Aix-en-Provence, France
^jDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
^kUniversité Lorraine and CNRS, CRPG, UPR 2300, Vandoeuvre les Nancy, F-54501, France

The Paris chondrite provides an excellent opportunity to study CM chondrules and refractory inclusions in a more pristine state than currently possible from other CMs, and to investigate the earliest stages of aqueous alteration captured within a single CM bulk composition. It was found in the effects of a former colonial mining engineer and may have been an observed fall. The texture, mineralogy, petrography, magnetic properties and chemical and isotopic compositions are consistent with classification as a CM2 chondrite. There are ~45 vol% high-temperature components mainly Type I chondrules (with olivine mostly Fa_0-2, mean Fa_0.9) with granular textures because of low mesostasis abundances. Type II chondrules contain olivine Fa₇ to Fa₇₆. These are dominantly of Type IIA, but there are IIAB and IIB chondrules, II(A)B chondrules with minor highly ferroan olivine, and IIA(C) with augite as the only pyroxene. The refractory inclusions in Paris are amoeboid olivine aggregates (AOA) and fine-grained spinel-rich Ca-Al-rich inclusions (CAI). The CAI phases formed in the sequence hibonite, perovskite, grossite, spinel, gehlenite, anorthite, diopside/fassaite and forsterite. The most refractory phases are embedded in spinel, which also occurs as massive nodules. Refractory metal nuggets are found in many CAI and refractory platinum group element abundances (PGE) decrease following the observed condensation sequences of their host phases. Mn-Cr isotope measurements of mineral separates from Paris define a regression line with a slope of ⁵³Mn/⁵⁵Mn = (5.76±0.76)×10⁶. If we interpret Cr isotopic systematics as dating Paris components, particularly the chondrules, the age is 4566.44 ± 0.66 Myr, which is close to the age of CAI and puts new constraints on the early evolution of the solar system. Eleven individual Paris samples define an O isotope mixing line that passes through CM2 and CO3 falls and indicates that Paris is a very fresh sample, with variation explained by local differences in the extent of alteration. The anhydrous precursor to the CM2s was CO3-like, but the two groups differed in that the CMs accreted a higher proportion of water. Paris has little matrix (~47%, plus 8% fine grained rims) and is less altered than other CM chondrites. Chondrule silicates (except mesostasis), CAI phases, submicron forsterite and amorphous silicate in the matrix are all well preserved in the freshest domains, and there is abundant metal preserved (metal alteration stage 1 of Palmer E. E. and D. S. Lauretta (2011) Aqueous alteration of kamacite in CM chondrites, Meteor. Planet. Sci. 46, 1587–1607). Metal and sulfide compositions and textures correspond to the least heated or equilibrated CM chondrites, Category A of Kimura M., Grossman J. N. and Weisberg M. K. (2011) Fe-Ni metal and sulfide minerals in CM chondrites, An indicator for thermal history.Meteor. Planet. Sci. 46, 431–442. The composition of tochilinite-cronstedtite intergrowths gives a PCP index of ~2.9. Cronstedtite is more abundant in the more altered zones whereas in normal highly altered CM chondrites, with petrologic subtype 2.6-2.0 based on the S/SiO₂ and ∑FeO/SiO₂ ratios in PCP or tochilinite-cronstedtite intergrowths (Rubin A. E., Trigo-Rodrıguez J. M., Huber H. and Wasson J. T. (2007) Progressive aqueous alteration of CM carbonaceous chondrites Geochim. Cosmochim. Acta 71, 2361-2382), cronstedtite is destroyed by alteration. The matrix in fresh zones has CI chondritic volatile element abundances, but interactions between matrix and chondrules occurred during alteration, modifying the volatile element abundances in the altered zones. Paris has higher trapped Ne contents, more primitive organic compounds, and more primitive organic material than other CMs. There are gradational contacts between domains of different degree of alteration, on the scale of ~1 cm, but also highly altered clasts, suggesting mainly a water-limited style of alteration, with no significant metamorphic reheating.

Reference
Hewins RH, Zanda B, Leroux H, Barrat J-A, Humayun M, Göpel C, Greenwood RC, Franchi IA, Pont S, Lorand J-P, Cournède C, Gattacceca J, Rochette P, Kuga M, Marrocchi Y and Marty B (in press) The Paris meteorite, the least altered CM chondrite so far. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.09.014]
Copyright Elsevier

Link to Article

T. G. Müller¹, T. Miyata², C. Kiss³, M. A. Gurwell⁴, S. Hasegawa⁵, E. Vilenius¹, S. Sako², T. Kamizuka², T. Nakamura⁶, K. Asano², M. Uchiyama², M. Konishi², M. Yoneda⁷, T. Ootsubo⁸, F. Usui⁵, Y. Yoshii², M. Kidger⁹, B. Altieri⁹, R. Lorente⁹, A. Pál³, L. O’Rourke⁹ and L. Metcalfe⁹

¹Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, Postfach 1312, 85741 Garching, Germany
²Institute of Astronomy, School of Science, the University of Tokyo, 2-21-1 Osawa, Mitaka, 181-0015 Tokyo, Japan
³Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege 15-17, 1121 Budapest, Hungary
⁴Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Kanagawa, Japan
⁶Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, 113-0033 Tokyo, Japan
⁷Planetary Plasma and Atmospheric Research Center, Tohoku University, Aramaki, Aoba-ku, 980-8578 Sendai, Japan
⁸Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, 980-8578 Sendai, Japan
⁹European Space Astronomy Centre (ESAC), European Space Agency, Apartado de Correos 78, 28691 Villanueva de la Cañada, Madrid, Spain

The near-Earth asteroid 308635 (2005 YU₅₅) is a potentially hazardous asteroid which was discovered in 2005 and passed Earth on Nov. 8, 2011 at 0.85 lunar distances. This was the closest known approach by an asteroid of several hundred metres in diameter since 1976 when an object of similar size passed at 0.5 lunar distances. We observed 2005 YU₅₅ from the ground with a recently developed mid-IR camera (miniTAO/MAX38) in N and Q bands and with the Submillimeter Array (SMA) at 1.3 mm. In addition, we obtained space observations with Herschel/PACS at 70, 100, and 160 μm. Our thermal measurements cover a wide range of wavelengths from 8.9 μm to 1.3 mm and were taken after opposition at phase angles between –97° and –18°. We performed a radiometric analysis via a thermophysical model and combined our derived properties with results from radar, adaptive optics, lightcurve observations, speckle, and auxiliary thermal data. We find that 308635 (2005 YU₅₅) has an almost spherical shape with an effective diameter of 300 to 312 m and a geometric albedo p_V of 0.055 to 0.075. Its spin axis is oriented towards celestial directions (λ_ecl, β_ecl) = (60° ± 30°, –60° ± 15°), which means it has a retrograde sense of rotation. The analysis of all available data combined revealed a discrepancy with the radar-derived size. Our radiometric analysis of the thermal data together with the problem to find a unique rotation period might be connected to a non-principal axis rotation. A low to intermediate level of surface roughness (rms mean slope in the range 0.1–0.3) is required to explain the available thermal measurements. We found a thermal inertia in the range 350−800 Jm^-2 s^-0.5 K^-1, very similar to the rubble-pile asteroid 25 143 Itokawa and indicating a surface with a mixture of low conductivity fine regolith with larger rocks and boulders of high thermal inertia.

Reference
Müller TG, Miyata T, Kiss C, Gurwell MA, Hasegawa S, Vilenius E, Sako S, Kamizuka T, Nakamura T, Asano K, Uchiyama M, Konishi M, Yoneda M, Ootsubo T, Usui F, Yoshii Y, Kidger M, Altieri B, Lorente R, Pál A, O’Rourke L, and Metcalfe L (in press) Physical properties of asteroid 308635 (2005 YU55) derived from multi-instrument infrared observations during a very close Earth approach. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321664]
Reproduced with permission © ESO

Link to Article