Enstatite chondrite meteorites date the giant planet instability

The identification of meteorite parent bodies provides the context for understanding planetesimal formation and evolution as well as the key solar system dynamical events they have witnessed. We identified that the family of asteroid fragments whose largest member is asteroid (161) Athor is the unique source of the rare EL enstatite chondrite meteorites (Avdellidou et al. 2022), 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 (Delbo et al. 2019), however the diameter of the Athor family progenitor was much smaller than the putative size of the EL original planetesimal (Triellof et a. 2022). Therefore, we deduced 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. 

We investigated the possible ways that could have brought the Athor family progenitor in its current position in the inner main belt. To do so, we used an interdisciplinary methodology where we combined laboratory meteorite thermochronometric data, thermal modelling, and dynamical simulations. 

We showed that planetesimal fragments from the terrestrial zone must have been implanted into the main asteroid belt at least 60 Myr after the beginning of the solar system. We concluded that the giant planet instability is the only dynamical process that can enable such implantation so late in the solar system timeline. 

Acknowledgements. We acknowledge support from the ANR ORIGINS (ANR- 18-CE31-0014). This work is based on data provided by the Minor Planet Physical Properties Catalogue (MP3C) of the Observatoire de la Côte d’Azur (mp3c.oca.eu).

References:

Avdellidou, Delbo, A. Morbidelli, Walsh, Munaibari, Bourdelle de Micas, Devogèle, Fornasier, Gounelle, & van Belle. Athor asteroid family as the source of the EL enstatite meteorites, 2022, A&A, 665, id.L9, 13 pp.

Delbo, Avdellidou, & Morbidelli, Ancient and primordial collisional families as the main sources of X-type asteroids of the inner main belt, 2019, A&A, 624, A69 

Trieloff, Hopp & Gail. Evolution of the parent body of enstatite (EL) chondrites, 2022, Icarus, 373, 114762