Noël Chaumard^1,2,3,†, Bertrand Devouard^1,2,3,‡, Audrey Bouvier^4,§, Meenakshi Wadhwa⁴

¹Laboratoire Magmas et Volcans, Clermont Université, Université Blaise Pascal, Clermont-Ferrand, France
²CNRS, UMR 6524, LMV, Clermont-Ferrand, France
³IRD, R 163, LMV, Clermont-Ferrand, France
⁴Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
^†Laboratoire de Minéralogie et de Cosmochimie du Muséum, Muséum National d’Histoire Naturelle, UMR 7202 – CNRS, Paris, France
^‡Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Aix en Provence, France
^§University of Western Ontario, Department of Earth Sciences, London, Ontario, Canada

CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. Although CKs are described as calcium-aluminum-rich inclusion (CAI)-poor objects, the abundance of CAIs in the 18 CK3–6 we analyzed ranges from zero to approximately 16.4%. During thermal metamorphism, some of the fine-grained CAIs recrystallized as irregular assemblages of plagioclase + Ca-rich pyroxene ± olivine ± Ca-poor pyroxene ± magnetite. Coarse-grained CAIs display zoned spinel, fassaite destabilization, and secondary grossular and spinel. Secondary anorthite, grossular, Ca-rich pyroxene, and spinel derive from the destabilization of melilite, which is lacking in all CAIs investigated. The Al-Mg isotopic systematics measured in fine- and coarse-grained CAIs from Tanezrouft (Tnz) 057 was affected by Mg redistribution. The partial equilibration of Al-Mg isotopic signatures obtained in the core of a coarse-grained CAI (CG1-CAI) in Tnz 057 may indicate a lower peak temperature for Mg diffusion of approximately 540–580 °C, while grossular present in the core of this CAI indicates a higher temperature of around 800 °C for the metamorphic event on the parent body of Tnz 057. Excluding metamorphic features, the similarity in nature and abundance of CAIs in CK and CV chondrites confirms that CVs and CKs form a continuous metamorphic series from type 3 to 6.

Reference
Chaumard N, Devouard B, Bouvier A and Wadhwa M (in press) Metamorphosed calcium-aluminum-rich inclusions in CK carbonaceous chondrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12260]
Published by arrangement with John Wiley & Sons

Link to Article

Edward A. Cloutis¹, Richard P. Binzel² and Michael J. Gaffey³

¹Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada
²Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 54-426, Cambridge, MA 02139, USA
³Department of Space Studies, University of North Dakota, Box 9008, Grand Forks, ND 58202-9008, USA

Asteroids are arguably the most accessible remnants of building blocks of the early Solar System and an essential piece of the terrestrial planet–formation puzzle. Determining their compositions and physical properties can provide important and otherwise unobtainable information concerning the origin, structure, and dynamic history of the Solar System, as well as insights into the sources of materials from which the terrestrial planets were constructed. Our understanding of the compositional structure of the asteroid belt and of individual asteroids has advanced significantly since the 1970s. Strong associations between asteroids and meteorites are emerging thanks to multitechnique observations, the synthesis of observations and modeling, in situ measurements, and sample-return missions.

Reference
Cloutis EA, Binzel RP and Gaffey MJ (2014) Establishing Asteroid–Meteorite Links. Elements  10:25-30.
[doi:10:11-17.10.2113/gselements.10.1.25]
Copyright: The Mineralogical Society of America

Link to Article

Patrick Michel

Lagrange Laboratory, University of Nice-Sophia Antipolis, CNRS, Côte d’Azur Observatory, CS 34229, 06304 Nice Cedex 4, France

Asteroids are the leftover precursors to the terrestrial planets. Before the first images of them were sent from space, our knowledge of asteroids relied entirely on ground-based observations and meteorite analysis. Spacecraft images revolutionized our knowledge and geological understanding of their physical properties. They also showed us that asteroids are subjected to various kinds of processes and are incredibly diverse in size, shape, structure, composition, and rotational properties. Therefore, space missions remain necessary to enhance our knowledge of the various components of the asteroid population. In addition, numerical modeling is required to interpret spacecraft images and improve our understanding of the physical processes asteroids experience over their lifetime.

Reference
Michel P (2014) Formation and Physical Properties of Asteroids. Elements 10:19-24.
[doi:10.2113/gselements.10.1.19]
Copyright: The Mineralogical Society of America

Link to Article

Guy Libourel¹ and Catherine M. Corrigan²

¹Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, and CRPG, CNRS UMR 7358, Université de Lorraine BP20, 54501 Vandœuvre les Nancy, France
²Smithsonian Institution, National Museum of Natural History 10th St. and Constitution Ave. NW, MRC 119, Washington, DC 20056, USA

At present, we know of ~600,000 asteroids in the asteroid belt, and there are very likely millions more. Orbiting the Sun between Mars and Jupiter, they are thought to be the shattered remnants of small bodies formed within the young Sun’s solar nebula that never accreted enough material to become planets. These “minor bodies” are therefore keys to understanding how the Solar System formed and evolved. As leftover planetary building blocks, they are of great importance in understanding planetary compositions. They may also provide clues to the origin of life, as similar bodies may have delivered organics and water to the early Earth. For these reasons, several international space agencies have funded sample-return missions to asteroids.

Reference
Libourel G and Corrigan CM (2014) Asteroids: New Challenges, New Targets. Elements 10:11-17.
[doi:10.2113/gselements.10.1.11]
Copyright: The Mineralogical Society of America

Link to Article