^1,2J. Mah,³R. Brasser,^4,5J. M. Y. Woo,^3,7,8A. Bouvier,¹S. J. Mojzsis
Astronomy & Astrophysics 660, A36 Open Access Link to Article [DOI https://doi.org/10.1051/0004-6361/202142926]
¹Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²Earth Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan
³Origins Research Institute, Research Centre for Astronomy and Earth Sciences, 15–17 Konkoly Miklós Thege utca, 1121 Budapest, Hungary
⁴Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
⁵Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
⁶Bayerisches Geoinstitut, Universität Bayreuth, 95447 Bayreuth, Germany
⁷Department of Lithospheric Research, University of Vienna, 1090 Vienna, Austria
⁸Department of Geological Sciences, University of Colorado Boulder, Boulder, CO 80309-0399, USA
Reproduced with permisson (C)ESO

Not only do the sampled terrestrial worlds (Earth, Mars, and asteroid 4 Vesta) differ in their mass-independent (nucleosynthetic) isotopic compositions of many elements (e.g. ε48Ca, ε50Ti, ε54Cr, ε92Mo), the magnitudes of some of these isotopic anomalies also appear to correlate with heliocentric distance. While the isotopic differences between the Earth and Mars may be readily accounted for by the accretion of mostly local materials in distinct regions of the protoplanetary disc, it is unclear whether this also applies to asteroid Vesta. Here we analysed the available data from our numerical simulation database to determine the formation location of Vesta in the framework of three planet-formation models: classical, Grand Tack, and Depleted Disc. We find that Vesta has a high probability of forming locally in the asteroid belt in models where material mixing in the inner disc is limited; this limited mixing is implied by the isotopic differences between the Earth and Mars. Based on our results, we propose several criteria to explain the apparent correlation between the different nucleosynthetic isotopic compositions of the Earth, Mars, and Vesta: (1) these planetary bodies accreted their building blocks in different regions of the disc, (2) the inner disc is characterised by an isotopic gradient, and (3) the isotopic gradient was preserved during the formation of these planetary bodies and was not diluted by material mixing in the disc (e.g. via giant planet migration).

¹C. Avdellidou (Χ. Αβδελλίδου),¹M. Delbo,¹A. Morbidelli,²K. J. Walsh,^1,3E. Munaibari,⁴J. Bourdelle de Micas,⁵M. Devogèle,^4,6S. Fornasier,⁷M. Gounelle,⁸G. van Belle
Astronomy & Astrophysics 665, L9 Open Access Link to Article [DOI https://doi.org/10.1051/0004-6361/202244590]
¹Université Côte d’Azur, CNRS – Lagrange, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice Cedex 4, France
²Southwest Research Institute, 1050 Walnut St. Suite 300, Boulder, CO 80302, USA
³Université Côte d’Azur, CNRS – Géoazur, Observatoire de la Côte d’Azur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France
⁴LESIA, Université Paris Cité, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 92190 Meudon, France
⁵Arecibo Observatory, University of Central Florida, HC-3 Box 53995 Arecibo, PR 00612, USA
⁶Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris Cedex 05, France
⁷Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, IMPMC – UMR CNRS 7590, 57 rue Cuvier, 75005 Paris, France
⁸Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
Reproduced with permission (C)ESO

The identification of meteorite parent bodies provides the context for understanding planetesimal formation and evolution as well as the key Solar System events they have witnessed. However, identifying such links has proven challenging and some appear ambiguous. Here, we identify that the family of asteroid fragments whose largest member is (161) Athor is the unique source of the rare EL enstatite chondrite meteorites, the closest meteorites to Earth in terms of their isotopic ratios. The Athor family was created by the collisional fragmentation of a parent body 3 Gyr ago in the inner main belt. We calculate that the diameter of the Athor family progenitor was 64 km in diameter, much smaller than the putative size of the EL original planetesimal. Therefore, we deduce that the EL planetesimal that accreted in the terrestrial planet region underwent a first catastrophic collision in that region, and one of its fragments suffered a more recent catastrophic collision in the main belt, generating the current source of the EL meteorites.

¹Stefan Schröder et al. (>10)
Astronomy & Astrophysics 666, A164 Open Access Link to Article [DOI https://doi.org/10.1051/0004-6361/202244059]
¹Luleå University of Technology, 98128 Kiruna, Sweden
Reproduced with permission (C) ESO

Context. After landing on C-type asteroid Ryugu, MASCOT imaged brightly colored, submillimeter-sized inclusions in a small rock. Hayabusa2 successfully returned a sample of small particles from the surface of Ryugu, but none of these appear to harbor such inclusions. The samples are considered representative of Ryugu.

Aims. To understand the apparent discrepancy between MASCOT observations and Ryugu samples, we assess whether the MASCOT landing site, and the rock by implication, is perhaps atypical for Ryugu.

Methods. We analyzed observations of the MASCOT landing area acquired by three instruments on board Hayabusa2: a camera (ONC), a near-infrared spectrometer (NIRS3), and a thermal infrared imager. We compared the landing area properties thus retrieved with those of the average Ryugu surface.

Results. We selected several areas and landforms in the landing area for analysis: a small crater, a collection of smooth rocks, and the landing site itself. The crater is relatively blue and the rocks are relatively red. The spectral and thermophysical properties of the landing site are very close to those of the average Ryugu surface. The spectral properties of the MASCOT rock are probably close to average, but its thermal inertia may be somewhat higher.

Conclusions. The MASCOT rock can also be considered representative of Ryugu. Some of the submillimeter-sized particles in the returned samples stand out because of their atypical spectral properties. Such particles may be present as inclusions in the MASCOT rock.