Speaker
Description
Subsequent to the Moon’s formation, late accretion to the terrestrial planets strongly modified the physical and chemical nature of their silicate crusts and mantles. Here, dynamical N-body and Monte Carlo simulations are combined to determine impact probabilities, impact velocities, and expected mass augmentation onto the terrestrial planets from three sources: planetesimals left over from primary accretion, asteroids from the hypothetical E-belt, and comets arriving from the outer Solar System. I present new estimates of the amount of cometary material striking the terrestrial planets in an early (ca. 4480 Ma) episode of planetesimal-driven giant planet migration (Mojzsis et al. 2019; Brasser, Werner & Mojzsis 2019). The Moon and Mars suffer proportionally higher cometary accretion than Venus and Earth at late accretion. The background mass addition from small leftover planetesimals to Earth and Mars is far less than independent estimates based on geochemical tracers. This supports the theory that both planets were struck by single large bodies that delivered most of their terminal mass augmentation since primary accretion, rather than a throng of smaller impactors. I also present new fits to the impact chronologies valid from 4500 Ma to ca. 3700 Ma by which time the low number of planetesimals remaining in the dynamical simulations causes the impact rate to drop artificially. This temporal interval in solar system evolution, termed late accretion, thermally and chemically modified solid planetary surfaces and may have impeded life’s emergence on the Hadean (pre-3.85 Ga) Earth. I will conclude the presentation with amended global 3-D thermal analytical bombardment models derived from our new impact mass-production functions to show that persistent niches for prebiotic chemistry on the early Hadean Earth could endure late accretion a mere 170 Myr after the start of the solar system (Benner et al. 2019).
Benner, S.A., Bell, E.A., Biondi, E., Brasser, R., Carell, T., Kim, H-J., Mojzsis, S.J., Omran, A., Pasek, M.A., and Trail, D. (2019) When did Life Likely Emerge on Earth in an RNA-First Process? ChemSystemsChem Reviews DOI: 10.1002/syst.201900035.
Brasser, R., Werner, S.C., Mojzsis, S.J. (2019) Impact bombardment chronology of the terrestrial planets from 4.5 Ga to 3.5 Ga. in press - Icarus.
Mojzsis, S.J., Brasser, R., Kelly, N.M., Abramov, O., and Werner, S. (2019) Onset of giant planet migration before 4480 million years ago. The Astrophysical Journal, 881:44 (13pp), 2019 August 10 doi.org/10.3847/1538-4357/ab2c03.