^1,2Sébastien Charnoz, ³Jérôme Aleon, ⁴Noël Chaumard, ^1,2Kevin Baillie, ^1,3Esther Taillifet
¹Institut de Physique du Globe, Paris, France
²Laboratoire AIM, Université Paris Diderot /CEA/CNRS, Gif-sur-Yvette Cedex France
³Centre de Sciences Nucléaires et de Sciences de la Matière, CNRS/IN2P3 – Université Paris Sud, Bâtiment 104, 91405 Orsay campus, France
⁴Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Universités, Muséum National d’Histoire Naturelle, UPMC Univ. Paris 06, UMR CNRS 7590, IRD UMR 206, 61 rue Buffon, F-75005 Paris, France

Whereas it is generally accepted that calcium-aluminum-rich inclusions (CAIs) from chondritic meteorites formed in a hot environment in the solar protoplanetary disk, the conditions of their formation remain debated. Recent laboratory studies of CAIs have provided new kind of data: their size distributions. We report that size distributions of CAIs measured in laboratory from sections of carbonaceous chondrites have a power law size distribution with cumulative size exponent between -1.7 and -1.9, which translates into cumulative size exponent between -2.5 and -2.8 after correction for sectioning. To explain these observations, numerical simulations were run to explore the growth of CAIs from micrometer to centimeter sizes, in a hot and turbulent protoplanetary disk through the competition of coagulation and fragmentation. We show that the size distributions obtained in growth simulations are in agreement with CAIs size distributions in meteorites. We explain the CAI sharp cut-off of their size distribution at centimeter sizes as the direct result from the famous fragmentation barrier, provided that CAI fragment for impact velocities larger than 10 m/s. The growth/destruction timescales of millimeter- and centimeter-sized CAIs is inversely proportional to the local dust/gas ratio and is about 10 years at 1300 K and up to 104 years at 1670K. This implies that the most refractory CAIs are expected to be smaller in size owing to their long growth timescale compared to less refractory CAIs. Conversely, the least refractory CAIs could have been recycled many times during the CAI production era which may have profound consequences for their radiometric age.

Reference
Charnoz S, Aleon J, Chaumard N, Baillie K, Taillifet E (2015) Growth of calcium-aluminum-rich inclusions by coagulation and fragmentation in a turbulent protoplanetary disk: observations and simulations. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.023]

Copyright Elsevier

¹Maksimova, A.A., ^1,2Oshtrakh, M.I., ¹Petrova, E.V., ¹Grokhovsky, V.I., ^1,2Semionkin, V.A.
¹Department of Physical Techniques and Devices for Quality Control, Institute of Physics and Technology, Ural Federal UniversityEkaterinburg, Russian Federation
²Department of Experimental Physics, Institute of Physics and Technology, Ural Federal UniversityEkaterinburg, Russian Federation

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Maksimova AA, Oshtrakh MI, Petrova EV, Grokhovsky VI, Semionkin VA (2015) The 57Fe hyperfine interactions in the iron bearing phases in different fragments of Chelyabinsk LL5 meteorite: a comparative study using Mössbauer spectroscopy with a high velocity Resolution. Hyperfine Interactions (in Press)
Link to Article [DOI: 10.1007/s10751-014-1115-7]

¹Pechersky, ¹D.M., Markov, G.P. ,¹Tsel’movich, V.A.
¹Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. Bol’shaya Gruzinskaya 10Moscow, Russian Federation

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Reference
Pechersky DM, Markov GP, Tsel’movich VA (2015) Pure iron and other magnetic minerals in meteorites. Solar System Research 49, 61-71
Link to Article [DOI: 10.1134/S0038094614060070]

¹John P. Grotzinger, ²Joy A. Crisp, ²Ashwin R. Vasavada, MSL Science Team
¹Division of Geological and Planetary Sciences, California Institute of Technology
Pasadena, CA 91125, USA
E-mail: grotz@gps.caltech.edu
²Jet Propulsion Laboratory, California Institute of Technology
Pasadena, CA 91109, USA

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Reference
Grotzinger JP, Crisp JA, Vasavada AR, MSL Science Team (2015) Curiosity’s Mission of Exploration at Gale Crater, Mars. Elements 11, 19-26
Link to Article [doi: 10.2113/gselements.11.1.19]

¹Roger C. Wiens, ²Sylvestre Maurice, MSL Science Team
¹Los Alamos National LaboratoryLos Alamos, NM 87545, USA
²Institut de Recherche en Astrophysique et Planétologie
Toulouse, France

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Reference
Wiens RC, Maurice S, MSL Science Team (2015) ChemCam: Chemostratigraphy by the First Mars Microprobe. Elements 11, 33-38
Link to Article [doi: 10.2113/gselements.11.1.33]

¹Ralf Gellert, ²Benton C. Clark III, MSL and MER Science Teams
¹Department of Physics, University of Guelph
Guelph, ON N1G 2W1, Canada
E-mail: rgellert@uoguelph.ca
²Space Science Institute, Boulder, CO 80301, USA

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Reference
Gellert R, Clark III BC, MSL and MER Science Teams (2015) In Situ Compositional Measurements of Rocks and Soils with the Alpha Particle X-ray Spectrometer on NASA’s Mars Rovers. Elements 11, 39-44
Link to Article [doi: 10.2113/gselements.11.1.39]

¹Robert T. Downs, MSL Science Team
¹Department of Geosciences, University of Arizona
Tucson, AZ 85721-0077, USA

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Reference
Downs RT, MSL Science Team (2015) Determining Mineralogy on Mars with the CheMin X-Ray Diffractometer. Elements 11, 45-50
Link to Article [doi: 10.2113/gselements.11.1.45]

¹Paul R. Mahaffy, ²Pamela G. Conrad, MSL Science Team
¹Planetary Environments Laboratory, NASA Goddard Space Flight Center
Greenbelt, MD 20771, USA
²Planetary Environments Laboratory, NASA Goddard Space Flight Center
Greenbelt, MD 20771, USA

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Reference
Mahaffy PR, Conrad PG, MSL Science Team (2015) Volatile and Isotopic Imprints of Ancient Mars. Elements 11, 51-56

Link to Article [10.2113/gselements.11.1.51]

^1,2Tu-Han Luu, ³Edward D. Young, ^4,5Matthieu Gounelle, ²Marc Chaussidon
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG) – Institut National des Sciences de l’Univers CNRS – Université de Lorraine – UMR 7358, 54501 Vandoeuvre-lès-Nancy Cedex, France;
²Institut de Physique du Globe de Paris (IPGP), CNRS UMR 7154, Sorbonne Paris Cité, 75238 Paris Cedex 05, France;
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567;
⁴Institut de Minéralogie et de Physique des Milieux Condensés, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, Université Pierre et Marie Curie & L’Institut de Recherche pour le Développement, 75005 Paris, France; and
⁵Institut Universitaire de France, 75005 Paris, France

Chondritic meteorites are made of primitive components that record the first steps of formation of solids in our Solar System. Chondrules are the major component of chondrites, yet little is known about their formation mechanisms and history within the solar protoplanetary disk (SPD). We use the reconstructed concentrations of short-lived 26Al in chondrules to constrain the timing of formation of their precursors in the SPD. High-precision bulk magnesium isotopic measurements of 14 chondrules from the Allende chondrite define a 26Al isochron with 26Al/27Al = 1.2(±0.2) × 10−5 for this subset of Allende chondrules. This can be considered to be the minimum bulk chondrule 26Al isochron because all chondrules analyzed so far with high precision (∼50 chondrules from CV and ordinary chondrites) have an inferred minimum bulk initial (26Al/27Al) ≥ 1.2 × 10−5. In addition, mineral 26Al isochrons determined on the same chondrules show that their formation (i.e., fusion of their precursors by energetic events) took place from 0 Myr to ∼2 Myr after the formation of their precursors, thus showing in some cases a clear decoupling in time between the two events. The finding of a minimum bulk chondrule 26Al isochron is used to constrain the astrophysical settings for chondrule formation. Either the temperature of the condensation zone dropped below the condensation temperature of chondrule precursors at ∼1.5 My after the start of the Solar System or the transport of precursors from the condensation zone to potential storage sites stopped after 1.5 My, possibly due to a drop in the disk accretion rate.

Reference
Luua T-H, Young ED, Gounelle M, Chaussidon M (2015) Short time interval for condensation of high-temperature silicates in the solar accretion disk. Proceedings of the National Academy of Sciences 112,5, 1298–1303
Link to Article [doi: 10.1073/pnas.1414025112]

¹M. Jura, ²P. Dufour, ^1,3S. Xu, ¹B. Zuckerman, ¹B. Klein, ⁴E. D. Young, ⁵C. Melis
¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1562, USA
²Département de Physique, Université de Montréal, Montréal, Québec H3C 3J7, Canada
³European Southern Observatory (ESO), D-85748 Garching, Germany
⁴Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
⁵Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA

Using Keck/HIRES, we report abundances of 11 different elements heavier than helium in the spectrum of Ton 345, a white dwarf that has accreted one of its own minor planets. This particular extrasolar planetesimal, which was at least 60% as massive as Vesta, appears to have been carbon-rich and water-poor; we suggest it was compositionally similar to those Kuiper Belt Objects with relatively little ice.

Reference
Jura M, Dufour P, Xu S, Zuckerman B, Klein B, Young ED, Melis C (2015) Evidence for an Anhydrous Carbonaceous Extrasolar Minor Planet. The Astrophysical Journal  799 109
Link to Article [doi:10.1088/0004-637X/799/1/109]