The origin and evolution of stony meteorites

Abstract

Abstract. The origin of stony meteorites landing on Earth today is directly linked to the history of the main belt, which evolved both through collisional evolution and dynamical evolution/depletion. In this paper, we focus our attention on the main belt dynamical evolution scenario discussed in Petit et al. (2001). According to Petit et al., during the planet formation epoch, the primordial main belt contained several Earth masses of material, enough to allow the asteroids to accrete on relatively short timescales.After a few My, the accretion of planetary embryos in the main belt zone dynamically stirred the remaining planetesimals to high enough velocities to initiate fragmentation. After a short interval, perhaps as long as 10 My, the primordial main belt was dynamically depleted of > 99% of its material via the combined perturbations of the planetary embryos and a newly-formed Jupiter. The small percentage of objects that survived in the main belt zone became the asteroid belt. It has been shown that the wavy-shaped size-frequency distribution of the main belt is a "fossil" left over from this violent period .Using a collisional/dynamical model of this scenario, we tracked the evolution of stony meteoroids produced by catastrophic disruption events over the last several Gy. We show that most stony meteoroids are a byproduct of a collisional cascade derived from large and ancient asteroid families or smaller, more recent breakup events. The meteoroids are then delivered to Earth by drifting in semimajor axis via Yarkovsky thermal drag forces until they reach a resonance powerful enough to place them on an Earth-crossing orbit.

Yarkovsky footprints in the Eos family

“…Our value of γ is close to some previously reported values (e.g., Fujiwara, 1982) but discordant with some others who predict a considerably steeper distribution from their method (e.g., Tanga et al, 1999). This value of the power index suggests that the family has undergone significant collisional and dynamical evolution at small asteroid sizes that drove it toward the equilibrium state (e.g., Dohnanyi, 1969;O'Brien and Greenberg, 2003;Bottke et al, 2005c). In particular, Bottke et al (2005aBottke et al ( , 2005b estimate a 15-20 km size asteroid (roughly H = 11.5 for Eos family members) has a collisional lifetime of 2 Gyr; thus we would tentatively infer an age for the Eos family of 1-2 Gyr from this simple argument.…”

40Ar/39Ar impact ages and time–temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite

“…This scenario is tempting, although we note that it is in apparent contradiction with current orbital dynamic models of the asteroid belt that estimate a life span of several million of years for 10 km size asteroids (Bottke et al, 2005). The second possibility is that the Bunburra meteorite was shielded from impact heating by a protective blanket at least a few kilometers thick, and the specimen was excavated and liberated much later in the history of the parent body.…”

The peculiar case of the Agnia asteroid family

“…Using the code described in Bottke et al (2005c), we examined dust population from the present-day Agnia family. Our results suggest that Agnia-derived dust is likely to be 2-3 orders of magnitude smaller than that produced by the background main belt population.…”