火星の消えた大気は、見え隠れしている可能性がある(Mars’ missing atmosphere could be hiding in plain sight)

2024-09-25 マサチューセッツ工科大学(MIT)

＜関連情報＞

• https://news.mit.edu/2024/mars-missing-atmosphere-could-be-hiding-plain-sight-0925
• https://www.science.org/doi/10.1126/sciadv.adm8443

カンラン石の変質と火星初期の大気中の炭素の消失 Olivine alteration and the loss of Mars’ early atmospheric carbon

Joshua Murray and Oliver Jagoutz
Science Advances  Published:25 Sep 2024
DOI:https://doi.org/10.1126/sciadv.adm8443

Abstract

The early Martian atmosphere had 0.25 to 4 bar of CO₂ but thinned rapidly around 3.5 billion years ago. The fate of that carbon remains poorly constrained. The hydrothermal alteration of ultramafic rocks, rich in Fe(II) and Mg, forms both abiotic methane, serpentine, and high-surface-area smectite clays. Given the abundance of ultramafic rocks and smectite in the Martian upper crust and the growing evidence of organic carbon in Martian sedimentary rocks, we quantify the effects of ultramafic alteration on the carbon cycle of early Mars. We calculate the capacity of Noachian-age clays to store organic carbon. Up to 1.7 bar of CO₂ can plausibly be adsorbed on clay surfaces. Coupling abiotic methanogenesis with best estimates of Mars’ δ¹³C history predicts a reservoir of 0.6 to 1.3 bar of CO₂ equivalent. Such a reservoir could be used as an energy source for long-term missions. Our results further illustrate the control of water-rock reactions on the atmospheric evolution of planets.