¹Edward D. Young, ¹Issaku E. Kohl, ¹Paul H. Warren, ²David C. Rubie, ^2,3Seth A. Jacobson, ³Alessandro Morbidelli
¹Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA.
²Bayerisches Geoinstitut, University of Bayreuth, D-95490 Bayreuth, Germany.
³Laboratoire Lagrange, Université de Nice–Sophia Antipolis, Observatoire de la Cote d’Azur, CNRS, 06304 Nice, France.

Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ′17O of −1 ± 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Δ′17O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.

Reference
Young ED,Kohl IE,Warren PH,Rubie DC,Jacobson SA,Morbidelli A (2016) Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact. Science 351, 6272, 493-496
Link to Article [DOI: 10.1126/science.aad0525]
Reprinted with permission from AAAS

¹Y. Langevin et al. (>10)*
¹Institut d’Astrophysique Spatiale, CNRS/Univ. Paris-Sud, Orsay, France
*Find the extensive, full author and affiliation list on the publishers website

The COSIMA mass spectrometer on board the ROSETTA orbiter has collected dust in the near coma of comet 67P/Churyumov-Gerasimenko since August 11, 2014. The collected dust particles are identified by taking images with a microscope (COSISCOPE) under grazing incidence illumination before and after exposure of the target to cometary dust. More than 10,000 dust particles > 14 µm in size collected from August 11, 2014 to April 3, 2015 have been detected on three distinct target assemblies, including ∼ 500 dust particles with sizes ranging from 50 to more than 500 µm, that can be resolved by COSISCOPE (pixel size 14 µm). During this period, the heliocentric distance decreased from 3.5 AU to less than 2 AU. The collection efficiency on targets covered with “metal black” has been very high, due to the low relative velocity of incoming dust. Therefore, the COSISCOPE observations provide the first optical characterization of an unbiased sample of particles collected in the inner coma of a comet. The typology of particles > 100 µm in size is dominated by clusters with a wide range of structure and strength, most originating from the disruption of large aggregates (> 1 mm in size) shortly before collection. A generic relationship between these clusters and IDPs / Antarctic meteorites is likely in the framework of accretion models. About 15% of particles larger than 100 µm are compact particles with two likely contributions, one being linked to clusters and another leaving the cometary nucleus as single compact particles.

Reference
Langevin Y et al. (2016) Typology of dust particles collected by the COSIMA mass spectrometer in the inner coma of 67P/Churyumov Gerasimenko. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.027]
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