^1,2Amy L. Fagan, ^1,2,3Katherine H. Joy, ^1,2Donald D. Bogard, ^1,2David A. Kring

¹ Center for Lunar Science and Exploration, Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX, 77058, USA
² NASA Lunar Science Institute, Moffett Field, CA, USA
³ School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK

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Reference
Fagan AL, Joy KH, Bogard DD, Kring DA (2014) Ages of Globally Distributed Lunar Paleoregoliths and Soils from 3.9 Ga to the Present. Earth, Moon, and Planets 112, 1-4, 59-71

Link to Article [10.1007/s11038-014-9437-7]

¹N.A. Starkey, ¹I.A. Franchi, ² M.R. Lee

¹ Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA
² School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, UK

Two interplanetary dust particles (IDPs) investigated by NanoSIMS reveal diverse oxygen isotope compositions at the micrometer-scale. The oxygen isotope values recorded at different locations across the single IDP fragments cover a wider range than the bulk values available from all IDPs and bulk meteorites measured to date. Measurement of H, C, and N isotopes by NanoSIMS, and the use of scanning and transmission electron microscopy (SEM and TEM) to determine elemental compositions and textural information allows for a better understanding of the lithologies and organic signatures associated with the oxygen isotope features.

IDP Balmoral, a ∼15μm-sized fragment with a chondritic porous (CP) -IDP-like texture, contains a region a few micrometers in size characterised by 16O-depleted isotope signatures in the range δ17O, δ18O = +80 to +200 ‰. The remainder of the fragment has a more 16O-rich composition (δ18O = 0-20 ‰), similar to many other IDPs and bulk meteorites. Other than in discrete pre-solar grains, such extreme 16O-depletions have only been observed previously in rare components within the matrix of the Acfer 094 meteorite. However, TEM imaging and FeO/MgO/Si ion ratios indicate that the 16O-depleted regions in Balmoral did not form by the same mechanism as that proposed for the 16O-depleted phases in Acfer 094. As the level of 16O depletion is consistent with that expected from isotope selective self-shielding, it is likely that the 16O-depleted reservoir was located close to that where oxygen self-shielding effects were most pronounced (i.e. the outer solar nebula or even interstellar medium).

Individual regions within IDP Lumley cover a range in δ18O from -30 to +19 ‰, with the oxygen isotope values broadly co-varying with δD, δ13C, δ15N, light-element ratios and texture. The relationships observed in Lumley indicate that the parent body incorporated material at the micrometer-scale from discrete diverse isotopic reservoirs, some of which are represented by inner Solar System material but others which must have formed in the outer Solar System.

The IDP fragments support a model whereby primary dust from the early solar nebula initially formed a variety of reservoirs in the outer solar nebula, with those at lower AU incorporating a higher proportion of inner Solar System chondritic dust than those at larger AU. These reservoirs were subsequently disrupted into micrometer-sized clasts that were re-incorporated into IDP parent bodies, presumably at large AU. These results reveal that any models accounting for mixing processes in the early solar nebula must also account for the presence of an extremely 16O-depleted reservoir in the comet-forming region.

Reference
Starkey NA, Franchi IA, Lee MR (2014) Isotopic diversity in interplanetary dust particles and preservation of extreme 16O-depletion. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.07.011]

Copyright Elsevier

^1,2D. A. Nedelcu, ^2,1M. Birlan, ^1,2M. Popescu, ¹O. Bădescu and ¹D. Pricopi

¹ Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
e-mail: nedelcu@aira.astro.ro; mpopescu@aira.astro.ro; octavian@aira.astro.ro; dpricopi@aira.astro.ro
² Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
e-mail: mirel.birlan@imcce.fr

Aims. In this paper we report near-infrared spectroscopic observations of one of the largest potentially hazardous asteroids, (214869) 2007 PA8. Mineralogical analysis of this object was followed by the investigation of the dynamical delivery mechanism from its probable source region, based on long-term numerical integrations.

Methods. The spectrum of (214869) 2007 PA8 was analysed using the positions of 1 μm and 2 μm bands and by curve-matching with RELAB meteorites spectra. Its dynamical evolution was investigated by means of a 200 000-year numerical integration in the past of 1275 clones followed to the source region.

Results. (214869) 2007 PA8 has a very young surface with a composition more akin to H chondrites than to any other type of ordinary chondrite. It arrived from the outer Main Belt in the near-Earth space via the 5:2 mean motion resonance with Jupiter by eccentricity pumping. Identification of its source region far from (6) Hebe raises the possibility of the existence of a second parent body of the H chondrites that has a radically different post-accretion history. Future spectroscopic surveys in the 5:2 resonance region will most likely discover other asteroids with an H chondrite composition.

Reference
Nedelcu DA, Birlan M, Popescu M, Bădescu O, Pricopi D. (2014) Evidence for a source of H chondrites in the outer main asteroid belt. Astrophysics&Astronomy Letters 567, L7
Link to Article [http://dx.doi.org/10.1051/0004-6361/201423949]

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