5:15 PM - 6:45 PM
[PPS07-P20] Orbital evolution of small bodies in the inner solar system and mantle erosion of proto-Mercury by their impacts
Keywords:Mercury, N-body simulation, Impact
Mercury is a dense planet and is estimated to have a much higher core mass fraction than other rocky planets in the solar system. However, its origin is still unclear. One possible explanation for Mercury's high core mass fraction is a collisional scenario in which proto-Mercury with a chondritic bulk composition has lost a large part of its mantle layer in violent impacts.
Several studies of collisional scenarios have assumed giant impacts between protoplanets. Studies using SPH simulations have shown the impact conditions of a giant impact to form Mercury-like planets (e.g., Asphaug & Reufer 2014; Chau et al. 2018). However, some studies examining giant impacts that occur in the context of planet formation using N-body simulations have found that giant impacts that form Mercury-like planets are very rare (Clement et al. 2019; Franco et al. 2022).
Therefore, in this study, we investigate the possibility that mantle materials of proto-Mercury are gradually stripped away by a large number of planetesimal collisions that occur during the planet formation process, rather than a giant impact, ultimately forming Mercury's high core mass fraction. While a certain large impact velocity is required for small bodies such as planetesimals to strip away the mantle of large bodies (e.g., Hyodo & Genda 2020, 2021), we consider that the secular resonance near Mercury's orbit may play a role in causing high-velocity planetesimal impacts.
In this study, we calculate the orbital evolution of a large number of particles distributed in the inner solar system using N-body simulations and estimate the erosion (or accretion) mass from the impact conditions of the collisions that occur in our simulations. To calculate the erosion/accretion mass due to collisions, we use the scaling law derived by Hyodo & Genda (2020), which calculates the accretion/erosion mass from the impact velocity and the impact angle. In the presentation, we will present detailed results of the above calculations.
Several studies of collisional scenarios have assumed giant impacts between protoplanets. Studies using SPH simulations have shown the impact conditions of a giant impact to form Mercury-like planets (e.g., Asphaug & Reufer 2014; Chau et al. 2018). However, some studies examining giant impacts that occur in the context of planet formation using N-body simulations have found that giant impacts that form Mercury-like planets are very rare (Clement et al. 2019; Franco et al. 2022).
Therefore, in this study, we investigate the possibility that mantle materials of proto-Mercury are gradually stripped away by a large number of planetesimal collisions that occur during the planet formation process, rather than a giant impact, ultimately forming Mercury's high core mass fraction. While a certain large impact velocity is required for small bodies such as planetesimals to strip away the mantle of large bodies (e.g., Hyodo & Genda 2020, 2021), we consider that the secular resonance near Mercury's orbit may play a role in causing high-velocity planetesimal impacts.
In this study, we calculate the orbital evolution of a large number of particles distributed in the inner solar system using N-body simulations and estimate the erosion (or accretion) mass from the impact conditions of the collisions that occur in our simulations. To calculate the erosion/accretion mass due to collisions, we use the scaling law derived by Hyodo & Genda (2020), which calculates the accretion/erosion mass from the impact velocity and the impact angle. In the presentation, we will present detailed results of the above calculations.