New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment
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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DOI：
10.1016/j.gca.2014.09.010
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发表时间：
2014-11
影响因子：
5
通讯作者：
R. Court;M. Sephton
中科院分区：
文献类型：
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作者：
R. Court;M. Sephton
微流星体在进入大气层时的加热和烧蚀产生的挥发性气体能够改变大气化学、表面气候和可居住性。我们对含碳微流星体Orgueil（CI 1）、ALH 88045（CM 1）、Cold Bokkeveld（CM 2）、Murchison（CM 2）和Mokoia（CV 3）的粉末样品进行了分步热解-傅里叶变换红外光谱分析，以模拟微流星体进入大气，并定量测定不同温度下水、二氧化碳和二氧化硫的产率，提供了对其源相性质的深入了解。我们已经将这些数据纳入最近开发的晚期重轰炸（LHB）的E带模型，以估计大约40亿年前地球和火星微流星体下落时挥发物的产生。目前，到达地球的微流星体的4（±2）× 1010 g/年产生约2.5（±1.3）× 109 g/年，土著水，4.1（±2.2）× 109 g/年-1总水量，1.9（±1.0）× 109 g yr− 1的二氧化碳和约1.1（±0.6）× 109 g yr− 1的二氧化硫，其中“原生”水排除了在250 °C的初始热解步骤中形成的水。对于火星来说，6.8 × 109 g/年的微流星体的流入产生了3.6（±1.9）× 108 g/年的原生水，6.4（±3.4）× 108 g/年的总水，2.4（±1.3）× 108 g/年的二氧化碳和1.5（±0.8）× 108 g/年的二氧化硫。LHB与微流星体的质量有关，在地球为1.3（±0.8）× 1022 g，在火星为2.3（±1.3）× 1021 g。对于地球来说，这个质量估计产生了8.3（±4.9）× 1020 g土著水，1.4（±0.8）× 1021 g总水分，6.3（±3.7）× 1020 g二氧化碳和3.8（±2.2）× 1020 g二氧化硫，LHB峰值5000万年时的生产率估计为5.1（±3.1）× 1012 g yr− 1的原生水，8.6（±5.1）× 1012 g yr− 1的总水量，3.9（±2.3）× 1012 g yr− 1的二氧化碳和2.3（±1.4）× 1012 g yr− 1的二氧化硫。对于火星，总产量为4.1-3.7 Ga，（±0.8）× 1020 g土著水，2.2（±1.3）× 1020 g总水分，9.3（±5.5）× 1019克二氧化碳和约5.8估计二氧化硫为（±3.4）× 1019克，5000万年峰值速率为8.2（±4.8）× 1011 g yr− 1的原生水，1.4（±0.8）× 1012 g yr− 1的总水量，5.8（±3.5）× 1011 g yr− 1的二氧化碳和3.6（±2.1）× 1011 g yr− 1的二氧化硫。这些对现今速率的估计误差主要是由LDEF的4（±2）× 1010 g yr− 1微流星体的数字的±50%的不确定性所决定的，而对古代速率的误差主要是由微流星体与小行星的质量比的类似的大不确定性所决定的。这些错误表明，有必要提高对陨石坠落率的理解，并改进太阳系演化的模型。目前早期地球和火星的气候模型主要关注火山释放的温室气体和气溶胶，但对地球外来源的关注较少。我们的数据量化了一个额外的外源性来源的挥发物，增加了内源性生产。
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) × 1010g yr−1of micrometeoroids arriving at Earth yield around 2.5 (±1.3) × 109g yr−1of indigenous water, 4.1 (±2.2) × 109g yr−1of total water, 1.9 (±1.0) × 109g yr−1of carbon dioxide and about 1.1 (±0.6) × 109g yr−1of sulphur dioxide, where “indigenous” water exclude water evolved at the initial pyrolysis step of 250 °C. For Mars, the infall of 6.8 × 109g yr−1of micrometeoroids yields 3.6 (±1.9) × 108g yr−1of indigenous water, 6.4 (±3.4) × 108g yr−1of total water, 2.4 (±1.3) × 108g yr−1of carbon dioxide and 1.5 (±0.8) × 108g yr−1of sulphur dioxide. The LHB is associated with micrometeoroidal infall masses of 1.3 (±0.8) × 1022g 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) × 1012g yr−1of indigenous water, 8.6 (±5.1) × 1012g yr−1of total water, 3.9 (±2.3) × 1012g yr−1of carbon dioxide and 2.3 (±1.4) × 1012g yr−1of sulphur dioxide. For Mars, total 4.1–3.7 Ga 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) × 1011g yr−1of indigenous water, 1.4 (±0.8) × 1012g yr−1of total water, 5.8 (±3.5) × 1011g yr−1of carbon dioxide and 3.6 (±2.1) × 1011g yr−1of sulphur dioxide. The errors in these estimates for the present-day rates are dominated by ±50% uncertainty in the LDEF figure of 4 (±2) × 1010g yr−1of 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.