Presentation Information
[PPS04-P27]Monte Carlo Simulations of atmospheric heating driven by celestial impacts on the proto-Earth
*Tatsuki Nawa1, Tomoki Kimura1, Tatsuya Yoshida2, Naoki Terada3 (1.Tokyo University of Science, 2.Institute of Science Tokyo, 3.Tohoku University)
Keywords:
atmosphere,asteroid impact,Earth
Earth formed through the collisional accretion of planetesimals in the protoplanetary disk, and once its mass reached that of the Moon or Mars, a proto-atmosphere developed via capture of primordial solar nebula gas and degassing from Earth's interior. After the giant impact at ~4.5 Ga, marking the end stage of accretion, a magma ocean and a massive water vapor atmosphere were formed. The evolution of a water vapor atmosphere strongly influences Earth's water inventory (Hamano et al., 2017). Because the proto-Earth experienced far more frequent impacts than the modern Earth during the magma ocean period, understanding impact-driven atmospheric heating and its temporal evolution in a water vapor atmosphere is essential for elucidating the atmospheric evolution. Recent studies suggest that the magma ocean may persist for nearly 10 million years (Yoshida et al., 2025); however, no previous studies have quantitatively evaluated the effects of celestial impacts over such a prolonged duration. Therefore, the overall contribution of celestial impacts to the evolution of the proto-Earth's atmosphere and water inventory has yet to be quantified.
Here we constructed a stochastic Monte Carlo model which statistically describes the impactor size-frequency distribution during the magma ocean period (Marchi et al., 2014; Sakuraba et al., 2021) for impactors colliding with the proto-Earth. With our Monte Carlo model, we developed an analytical model for the kinetic energy deposition of an impactor entering the atmosphere (Collins et al., 2005) to quantitatively evaluate the effects of impacts on the atmospheric evolution. We adopted the massive water vapor atmosphere proposed by Yoshida et al. (2025) during the magma ocean period. Model calculations indicated that frequent small impacts result in cumulative atmospheric heating rates of ~10^(-10) J m^(-3) s^(-1), averaged globally (~10^17 m^3) and over the magma ocean period, assumed to be ~25 Myr following Marchi et al. (2014), at altitudes of 0-200 km. This value is approximately three orders of magnitude smaller than the atmospheric heating rates of ~10^(-7) J m^(-3) s^(-1) due to the solar radiation at the same altitudes. In contrast, a single small impact can generate instantaneous and locally extreme atmospheric heating near an impactor during atmospheric entry. When averaged over the impacted atmospheric volume (~10^13 m^3) and the impact duration (~43 s), the heating rates reach ~10^8 J m^(-3) s^(-1), which is approximately 15 orders of magnitude greater than heating due to solar radiation. Such intense, localized heating may dissociate atmospheric chemical species, forming vapor plumes with non-equilibrium compositions, and thereby significantly altering atmospheric chemical composition.
In addition to atmospheric heating, we evaluated the atmospheric water budget based on the balance between the impact induced atmospheric erosion and water replenishment (Svetsov et al., 2000; Broadley et al., 2022), assuming the same impactor size-frequency distribution (Marchi et al., 2014; Sakuraba et al., 2021). Our calculations showed that meteorites with low water content of ~0.1 wt.%, such as enstatite chondrites, lead to net water loss because atmospheric erosion exceeds replenishment. Conversely, meteorites with high water content of ~10.0 wt.%, such as carbonaceous chondrites, do not significantly change the water inventory because replenishment balances erosion. However, the cumulative water contribution from such impacts was found to be limited to at most ~10^15-10^16 kg, which is 5-6 orders of magnitude smaller than the total planetary water inventory of ~10^21-10^22 kg during the magma ocean period (Yoshida et al., 2025). Consequently, although frequent small impacts during the magma ocean period may either maintain or reduce the water inventory depending on their composition, their quantitative contribution to the evolution of a planet's overall water inventory is limited.
Our results suggest that while frequent small impacts contribute little to the long-term thermal evolution of the water vapor atmosphere or the planetary water inventory, they may have affected the early Earth environment through changes in the atmospheric chemical composition caused by the instantaneous and local atmospheric heating.
Here we constructed a stochastic Monte Carlo model which statistically describes the impactor size-frequency distribution during the magma ocean period (Marchi et al., 2014; Sakuraba et al., 2021) for impactors colliding with the proto-Earth. With our Monte Carlo model, we developed an analytical model for the kinetic energy deposition of an impactor entering the atmosphere (Collins et al., 2005) to quantitatively evaluate the effects of impacts on the atmospheric evolution. We adopted the massive water vapor atmosphere proposed by Yoshida et al. (2025) during the magma ocean period. Model calculations indicated that frequent small impacts result in cumulative atmospheric heating rates of ~10^(-10) J m^(-3) s^(-1), averaged globally (~10^17 m^3) and over the magma ocean period, assumed to be ~25 Myr following Marchi et al. (2014), at altitudes of 0-200 km. This value is approximately three orders of magnitude smaller than the atmospheric heating rates of ~10^(-7) J m^(-3) s^(-1) due to the solar radiation at the same altitudes. In contrast, a single small impact can generate instantaneous and locally extreme atmospheric heating near an impactor during atmospheric entry. When averaged over the impacted atmospheric volume (~10^13 m^3) and the impact duration (~43 s), the heating rates reach ~10^8 J m^(-3) s^(-1), which is approximately 15 orders of magnitude greater than heating due to solar radiation. Such intense, localized heating may dissociate atmospheric chemical species, forming vapor plumes with non-equilibrium compositions, and thereby significantly altering atmospheric chemical composition.
In addition to atmospheric heating, we evaluated the atmospheric water budget based on the balance between the impact induced atmospheric erosion and water replenishment (Svetsov et al., 2000; Broadley et al., 2022), assuming the same impactor size-frequency distribution (Marchi et al., 2014; Sakuraba et al., 2021). Our calculations showed that meteorites with low water content of ~0.1 wt.%, such as enstatite chondrites, lead to net water loss because atmospheric erosion exceeds replenishment. Conversely, meteorites with high water content of ~10.0 wt.%, such as carbonaceous chondrites, do not significantly change the water inventory because replenishment balances erosion. However, the cumulative water contribution from such impacts was found to be limited to at most ~10^15-10^16 kg, which is 5-6 orders of magnitude smaller than the total planetary water inventory of ~10^21-10^22 kg during the magma ocean period (Yoshida et al., 2025). Consequently, although frequent small impacts during the magma ocean period may either maintain or reduce the water inventory depending on their composition, their quantitative contribution to the evolution of a planet's overall water inventory is limited.
Our results suggest that while frequent small impacts contribute little to the long-term thermal evolution of the water vapor atmosphere or the planetary water inventory, they may have affected the early Earth environment through changes in the atmospheric chemical composition caused by the instantaneous and local atmospheric heating.