David R. Frank^a, Michael E. Zolensky^b and Loan Le^a

^aESCG, NASA Johnson Space Center, Houston, TX 77058, USA
^bAstromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA

The dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the Wild 2 samples. We present 68 analyses of olivine (Fa_0-97) in the coarse-grained terminal particles of Stardust aerogel tracks and a comprehensive dataset (> 10³ analyses) of analogous olivine grains (5-30μm) isolated in CI, CM, CR, CH, CO, CV3-oxidized, CV3-reduced, C3-ungrouped (Acfer 094 and Ningqiang), L/LL 3.0-4, EH3, and Kakangari chondrite matrix. These compositions reveal that Wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite-forming regions. The Wild 2 olivine includes ameoboid olivine aggregates (AOAs), refractory forsterite, type I and type II chondrule fragments and/or microchondrules, and rare relict grain compositions. In addition, we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low-temperature, aqueous processing in the Kuiper Belt. The generally low Cr content of FeO-rich olivine in the Stardust samples indicates that they underwent mild thermal metamorphism, akin to a petrologic grade of 3.05-3.15.

Reference
Frank DR, Zolensky ME and Le L (in press) Olivine in terminal particles of Stardust aerogel tracks and analogous grains in chondrite matrix. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.05.037]
Copyright Elsevier

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Alan E. Rubin

Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA

MIL 11207 (R6) and LAP 04840 (R6) contain hornblende and phlogopite; MIL 07440 (R6) contains accessory titan-phlogopite and no hornblende. All three meteorites have been shocked: MIL 11207 contains extensive sulfide veins, pyroxene that formed from dehydrated hornblende, and an extensive network of plagioclase glass; MIL 07440 contains chromite-plagioclase assemblages, chromite veinlets and blebs, pincer-shaped plagioclase patches, but no sulfide veins; LAP 04840 contains olivine grains with chromite-bleb-laden cores and opaque-free rims, rare grains of pyroxene that formed from dehydrated hornblende, and no sulfide veins. These meteorites appear to have been heated to maximum temperatures of approximately 700–900 °C under conditions of moderately high PH₂O (perhaps 250–500 bars). All three samples underwent postshock annealing. During this process, olivine crystal lattices healed (giving the rocks the appearance of shock-stage S1), and diffusion of Fe and S from thin sulfide veins to coarse sulfide grains caused the veins to disappear in MIL 07440 and LAP 04840. This latter process apparently also occurred in most S1–S2 ordinary chondrites of high petrologic type. The pressure–temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers (as suggested in the literature). A giant impact or a series of smaller impacts would then have been required to excavate the hornblende- and biotite-bearing rocks and bring them closer to the surface. It was in that latter location where the samples were shocked, deposited in a hot ejecta blanket of low thermal diffusivity, and annealed.

Reference
Rubin AE (in press) Shock and annealing in the amphibole- and mica-bearing R chondrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12315]
Published by arrangement with John Wiley & Sons

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Andreas Morlok^a,b, Andrew B. Mason^c, Mahesh Anand^a,b, Carey Lisse^d, Emma S. Bullock^e and Monica Grady^a,b

^aDepartment of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
^bPlanetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA UK
^cFinnish Centre for Astronomy with ESO (FINCA), University of Turku, Tuorla Observatory, Väisäläntie 20, FI-21500 Piikkiö, Finland
^dJohns Hopkins University -APL, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
^eDepartment of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, USA

In order to link infrared observations of dust formed during planet formation in debris disks to mid-infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies, we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials, and of typical Martian meteorites.
A series of debris disk spectra characterized by a strong feature in the 9.0-9.5 μm range (HD23514, HD15407a, HD172555 and HD165014), is comparable to materials that underwent shock, collision or high temperature events. These are amorphous materials such as tektites, SiO₂-glass, obsidian, and highly shocked shergottites as well as inclusions from mesosiderites (Group A).
A second group (BD+20307, Beta Pictoris, HD145263, ID8, HD113766, HD69830, P1121, and Eta Corvi) have strong pyroxene and olivine bands in the 9-12 μm range and is very similar to ultramafic rocks (e.g. harzburgite, dunite)(Group B).
This could indicate the occurrence of differentiated materials similar to those in our Solar System in these other systems.
However, mixing of projectile and target material, as well as that of crustal and mantle material has to be taken into account in large scale events like hit-and-run and giant collisions or even large-scale planetary impacts. This could explain the olivine-dominated dust of group B.
The crustal-type material of group A would possibly require the stripping of upper layers by grazing-style hit-and run encounters or high energy events like evaporation/condensation in giant collisions. In tidal disruptions or the involvement of predominantly icy/water bodies the resulting mineral dust would originate mainly in one of the involved planetesimals. This could allow attributing the observed composition to a specific body (such as e.g. Eta Corvi).

Reference
Morlok M, Mason AB, Anand M, Lisse C, Bullock ES and Grady M (in press) Dust from collisions: A way to probe the composition of exo-planets?. Icarus
[doi:10.1016/j.icarus.2014.05.024]
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Daniel Herwartz^1,2, Andreas Pack¹, Bjarne Friedrichs¹ and Addi Bischoff³

¹Georg-August-Universität Göttingen, Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Goldschmidtstraße 1, 37073 Göttingen, Germany.
²Universität zu Köln, Institut für Geologie und Mineralogie, Zülpicher Straße 49a, 50674 Köln, Germany.
³Westfälische Wilhelms-Universität Münster, Institut für Planetologie, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.

The Moon was probably formed by a catastrophic collision of the proto-Earth with a planetesimal named Theia. Most numerical models of this collision imply a higher portion of Theia in the Moon than in Earth. Because of the isotope heterogeneity among solar system bodies, the isotopic composition of Earth and the Moon should thus be distinct. So far, however, all attempts to identify the isotopic component of Theia in lunar rocks have failed. Our triple oxygen isotope data reveal a 12 ± 3 parts per million difference in Δ¹⁷O between Earth and the Moon, which supports the giant impact hypothesis of Moon formation. We also show that enstatite chondrites and Earth have different Δ¹⁷O values, and we speculate on an enstatite chondrite–like composition of Theia. The observed small compositional difference could alternatively be explained by a carbonaceous chondrite–dominated late veneer.

Reference
Herwartz D, Pack A, Friedrichs B and Bischoff A (in press) Identification of the giant impactor Theia in lunar rocks. Science 344:1146.
[doi:10.1126/science.1251117]
Reprinted with permission from AAAS

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Tim Elliott

School of Earth Science, University of Bristol, Queen’s Road, Clifton BS8 1RJ, UK.

As in many building booms, planets were put together pretty rapidly. Transforming nebular dust to fully formed planets took less than ~100 million years of the ~4.5 billion years of solar system history. Accurate determination of the rates of planetary growth is key for understanding these tumultuous beginnings of the solar system, but obtaining high-precision ages on short-lived events that happened so long ago is a formidable challenge. On page 1150 of this issue, Kruijer et al. (1) determine with remarkable accuracy that planetary core formation began less than 1 million years after the first solids condensed—extraordinarily fast on geological time scales.

Reference
Elliot T (in press) Speed metal. Science 344:1086.
[doi:10.1126/science.1254943]
Reprinted with permission from AAAS

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T. S. Kruijer^1,2, M. Touboul³, M. Fischer-Gödde¹, K. R. Bermingham³, R. J. Walker³ and T. Kleine¹

¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, DE-48149 Münster, Germany.
²ETH Zürich, Inst. of Geochemistry and Petrology, Clausiusstrasse 25, CH-8092 Zürich, Switzerland.
³Department of Geology, University of Maryland, College Park, MD 20742, USA.

Understanding core formation in meteorite parent bodies is critical for constraining the fundamental processes of protoplanet accretion and differentiation within the solar protoplanetary disk. We report variations of 5 to 20 parts per million in ¹⁸²W, resulting from the decay of now-extinct ¹⁸²Hf, among five magmatic iron meteorite groups. These ¹⁸²W variations indicate that core formation occurred over an interval of ~1 million years and may have involved an early segregation of Fe-FeS and a later segregation of Fe melts. Despite this protracted interval of core formation, the iron meteorite parent bodies probably accreted concurrently ~0.1 to 0.3 million years after the formation of Ca-Al–rich inclusions. Variations in volatile contents among these bodies, therefore, did not result from accretion at different times from an incompletely condensed solar nebula but must reflect local processes within the nebula.

Reference
Kruijer TS, Touboul M, Fischer-Gödde M, Bermingham KR, Walker RJ and Kleine T (in press) Protracted core formation and rapid accretion of protoplanets. Science 344:1150.
[doi:10.1126/science.1251766]
Reprinted with permission from AAAS

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Seungwon Lee^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

We present sub-millimeter observations of the ground-state rotational transition (1₁₀–1₀₁) of water vapour from comet C/2002 T7 (LINEAR) obtained with the MIRO Instrument on the ESA Rosetta Spacecraft (s/c) Orbiter on April 30, 2004. At the time of the observations, the comet was at a distance of 0.63 AU from the Sun, 0.68 AU from the MIRO telescope, and about 7.5 days after its perihelion. The ground state rotation transition of ortho-water at 556.936 GHz was observed and integrated for ∼ 8 hours using a frequency switched radiometer to provide short and long term stability. The MIRO beam size is 7.5 arcmin in terms of full width half maximum, corresponding to a radius of 1.1×10⁵ km at the comet location. The observed signal line area of the water line spectrum is 4.3±0.8 K km/s. Using a molecular excitation and radiation transfer model and assuming the spherically symmetric and constant radial expansion of gas in the coma, we estimate that the production rate of water is (1.0±0.2)x10³⁰ molecules/s and the expansion velocity is 1.1±0.2 km/s at the time of the MIRO observation. The present estimation of the water outgassing rate of the comet is in good agreement with other observation-based estimations when the outgassing rates with respect to the time after perihelion are compared. The Doppler-correctd center velocity of the observed line was red-shifted by 0.67±0.13 km/s, of which only 0.18 km/s shift is explained by the model and attributed to a self-absorption effect. The potential sources of the additional red shift are discussed.

Reference
Lee et al. (in press) Sub-millimeter Observation of Water Vapor at 557 GHz in Comet C/2002 T7 (LINEAR). Icarus
[doi:10.1016/j.icarus.2014.05.004]
Copyright Elsevier

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Yayoi N. Miura¹, Keisuke Nagao² and Makoto Kimura³

¹Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo, Japan
²Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan
³Faculty of Science, Ibaraki University, Mito, Ibaraki, Japan

We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole-rock samples of the Allende CV3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic ³He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre-exposure evidence for the studied chondrules. Large amounts of ³⁶Ar, ^80,82Kr, and ¹²⁸Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [⁸⁰Kr]_n, from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic ¹²⁹Xe. The abundance ratios of radiogenic ¹²⁹Xe to neutron capture–produced ¹²⁸Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high-temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain ²⁴⁴Pu-derived fission Xe. The average²⁴⁴Pu/²³⁸U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.

Reference
Miura YN, Nagao K and Kimura M (in press) Noble gases in individual chondrules of the Allende CV3 chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12313]
Published by arrangement with John Wiley & Sons

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Masato Kiuchi and Akiko M. Nakamura

Department of Earth and Planetary Sciences, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501,Japan

We obtain an empirical relationship between porosity and the interparticle force of granular media based on measurement data on the ground. We apply the relationship to the condition of the surface of small bodies to estimate the porosity and the particle size of the regolith.

Reference
Kiuchi M and Nakamura AM (in press) Relationship between Regolith Particle Size and Porosity on Small Bodies. Icarus
[doi:10.1016/j.icarus.2014.05.029]
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Andrea Isella¹, Claire J. Chandler¹, John M. Carpenter¹, Laura M. Pérez^2,3 and Luca Ricci¹

³Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA
³National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801, USA
³Jansky Fellow.

We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa 15 b is a massive planet (>5 M_J ) accreting at a rate greater than 10⁶ M_J  yr^-1, then its circumplanetary disk is less massive than 0.1 M_J , or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimates are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5 × 10^-4 M_J and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star.

Reference
Isella A, Chandler CJ, Carpenter JM, Pérez LM and Ricci L (in press) Searching for Circumplanetary Disks around LkCa 15. The Astrophysical Journal 788:129.
[doi:10.1088/0004-637X/788/2/129]

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