^1,2J. de León et al. (>10)*
¹Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205, La Laguna, Spain
²Department of Astrophysics, University of La Laguna, 38205, Tenerife, Spain
*Find the extensive, full author and affiliation list on the publishers website

The Polana-Eulalia family complex is located in the inner part of the asteroid belt, bounded by the ν6ν6 and the 3:1 resonances, where we can find another three collisional families of primitive asteroids (Erigone, Clarissa, and Sulamitis), and a low-albedo population of background objects. This region of the belt is believed to be the most likely origin of the two primitive near-Earth asteroids that are the current targets of two sample return missions: NASA’s OSIRIS-REx and JAXA’s Hayabusa 2 to asteroids (101955) Bennu and (162173) Ryugu (also known as 1999 JU3), respectively. Therefore, understanding these families will enhance the scientific return of these missions.

We present the results of a spectroscopic survey of asteroids in the region of the Polana-Eulalia family complex, and also asteroids from the background population of low-albedo, low-inclination objects. We obtained visible spectra of a total of 65 asteroids, using the 10.4m Gran Telescopio Canarias (GTC) and the 3.6m Telescopio Nazionale Galileo (TNG), both located at the El Roque de Los Muchachos Observatory, in the island of La Palma (Spain), and the 3.6m New Technology Telescope (NTT), located at the European Southern Observatory of La Silla, in Chile. From the spectral analysis of our sample we found that, in spite of the presence of distinct dynamical groups, the asteroids in this region present spectral homogeneity at visible wavelengths, showing a continuum of spectral slopes, from blue to moderately red, typical of primitive asteroids classified as B- and C-types. We conclude that visible spectra can not be used to distinguish between members of the Polana and the Eulalia families, or members of the background population.

The visible spectra of the two targets of sample return missions, asteroids Bennu and Ryugu, are compatible with the spectra of the asteroids in this region, supporting previous studies that suggested either the Polana family or the background population as the most likely origins of these NEAs.

Reference
de León J et al. (2015) Visible Spectroscopy of the Polana-Eulalia Family Complex: Spectral Homogeneity. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.11.014]

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¹Caroline Fitoussi, ¹Bernard Bourdon,¹Xueying Wang
¹Laboratoire de Géologie de Lyon (Ecole Normale Supérieure de Lyon, CNRS and Université Claude Bernard de Lyon), ENS Lyon, 46 allée d’Italie, 69364 Lyon Cedex 07, France

The Earth formed in a swarm of Moon- to Mars-sized objects that collided together to build our planet. A large body of work has been dedicated to understanding the Earth’s composition as being made of single groups or mixtures of chondrites, however, these models cannot account for the isotopic and elemental characteristics of the Earth. Here, we test mixtures of meteorites, including achondrites, analyzed for seven isotope systems (O, Cr, Ni, Ti, Mo, Ca and Sr), to reproduce the isotope compositions of the Earth and Mars. Our Monte Carlo inversion (a numerical method based on generation of random numbers used to invert multiparameter models) yields a new compositional model where Earth and Mars come almost entirely from the same source material. This finding is in striking agreement with recent planetary formation models in which Earth and Mars formed in a common narrow zone of the protoplanetary disk with Mars being ejected to its current position which prevented further accretion. An important outcome of the model is that a significant mass fraction of the Earth could have been made of volatile depleted and refractory enriched planetary bodies such as angrites (among the oldest known achondrites). This conclusion is also in agreement with new Si isotope data in angrites which suggest that a component of angrites would help explain the difference in δ30Siδ30Si between the bulk silicate Earth and its building blocks. Our model matches all isotope compositions for both planets, reproduces the volatile element budget of Mars, and accounts for the enrichment in refractory elements of the Earth and Mars compared to chondrites.

Reference
Fitoussi C, Bourdon B, Wang X (2015) The building blocks of Earth and Mars: A close genetic link. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.11.036]

Copyright Elsevier