New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment

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Heating and ablation of micrometeoroids during atmospheric entry yields volatile gases capable of altering atmospheric chemistry, surface climate and habitability. We have subjected powdered samples of the carbonaceous chondrites Orgueil (CI1), ALH 88045 (CM1), Cold Bokkeveld (CM2), Murchison (CM2) and Mokoia (CV3) to stepped pyrolysis-Fourier transform infrared spectroscopy to simulate the atmospheric entry of micrometeoroids and to quantify the yields of water, carbon dioxide and sulphur dioxide at various temperatures, offering insights into the nature of their source phases. We have incorporated these data into the recently-developed E-Belt model of the Late Heavy Bombardment (LHB) to estimate the production of volatiles from infalling micrometeoroids at Earth and Mars around four billion years ago. At the present day, the 4 (±2)×1010gyr−1 of micrometeoroids arriving at Earth yield around 2.5 (±1.3)×109gyr−1 of indigenous water, 4.1 (±2.2)×109gyr−1 of total water, 1.9 (±1.0)×109gyr−1 of carbon dioxide and about 1.1 (±0.6)×109gyr−1 of sulphur dioxide, where “indigenous” water exclude water evolved at the initial pyrolysis step of 250°C. For Mars, the infall of 6.8×109gyr−1 of micrometeoroids yields 3.6 (±1.9)×108gyr−1 of indigenous water, 6.4 (±3.4)×108gyr−1 of total water, 2.4 (±1.3)×108gyr−1 of carbon dioxide and 1.5 (±0.8)×108gyr−1 of sulphur dioxide. The LHB is associated with micrometeoroidal infall masses of 1.3 (±0.8)×1022 g at Earth and 2.3 (±1.3)×1021g at Mars. For Earth, this mass is estimated to have produced 8.3 (±4.9)×1020g of indigenous water, 1.4 (±0.8)×1021g of total water, 6.3 (±3.7)×1020g of carbon dioxide and 3.8 (±2.2)×1020g of sulphur dioxide, with production rates in the peak 50 Myr of the LHB estimated at 5.1 (±3.1)×1012gyr−1 of indigenous water, 8.6 (±5.1)×1012 gyr−1 of total water, 3.9 (±2.3)×1012gyr−1 of carbon dioxide and 2.3 (±1.4)×1012gyr−1 of sulphur dioxide. For Mars, total 4.1–3.7Ga production of 1.3 (±0.8)×1020g of indigenous water, 2.2 (±1.3)×1020g of total water, 9.3 (±5.5)×1019g of carbon dioxide and around 5.8 (±3.4)×1019g of sulphur dioxide is estimated, with peak 50 Myr rates of 8.2 (±4.8)×1011gyr−1 of indigenous water, 1.4 (±0.8)×1012 gyr−1 of total water, 5.8 (±3.5)×1011gyr−1 of carbon dioxide and 3.6 (±2.1)×1011gyr−1 of sulphur dioxide. The errors in these estimates for the present-day rates are dominated by ±50% uncertainty in the LDEF figure of 4 (±2)×1010gyr−1 of micrometeoroids while the errors for the ancient rates are dominated by the similarly large uncertainty regarding the mass ratio of micrometeoroids to asteroids. These errors indicate the need for improved understandings of infall rates and better models of solar system evolution. Current models of climate for early Earth and Mars focus on volcanic outgassing for greenhouse gases and aerosols, but pay less attention to extraterrestrial sources. Our data quantify an additional exogenous source of volatiles that augments the endogenous production.