火星大気中の水素の持続性を説明 (Explaining Persistent Hydrogen in Mars’ Atmosphere)

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2025-01-27 ハーバード大学

ハーバード大学の研究チームは、火星の大気中に持続的に存在する水素の起源を解明しました。彼らの研究によれば、約40億年前から30億年前のノアキス紀とヘスペリアン紀において、火星は数百万年にわたる温暖な期間と寒冷な期間を繰り返していたとされています。温暖期には、地殻の水和反応により水素が大気中に放出され、二酸化炭素と結びついて温室効果を引き起こし、液体の水が存在する環境を維持していたと考えられます。この研究は、火星の気候変動と大気化学の関係を詳細にモデル化し、過去の火星における生命の起源や進化の理解に貢献するものです。

<関連情報>

初期火星における周期的な温暖気候は地殻の水和によってもたらされた Episodic warm climates on early Mars primed by crustal hydration

Danica Adams,Markus Scheucher,Renyu Hu,Bethany L. Ehlmann,Trent B. Thomas,Robin Wordsworth,Eva Scheller,Rob Lillis,Kayla Smith,Heike Rauer & Yuk L. Yung
Nature Geoscience  Published:15 January 2025
DOI:https://doi.org/10.1038/s41561-024-01626-8

火星大気中の水素の持続性を説明 (Explaining Persistent Hydrogen in Mars’ Atmosphere)

Abstract

Geological records indicate that the surface of ancient Mars harboured substantial volumes of liquid water, a resource gradually diminished by processes such as the chemical alteration of crustal materials by hydration and atmospheric escape. However, how a relatively warm climate existed on early Mars to support liquid water under a fainter young Sun is debated. Greenhouse gases such as H2 in a CO2-rich atmosphere could have contributed to warming through collision-induced absorption, but whether sufficient H2 was available to sustain warming remains unclear. Here we use a combined climate and photochemical model to simulate how atmospheric chemistry on early Mars responded to water–rock reactions and climate variations, as constrained by existing observations. We find that H2 outgassing from crustal hydration and oxidation, supplemented by transient volcanic activity, could have generated sufficient H2 fluxes to transiently foster warm, humid climates. We estimate that Mars experienced episodic warm periods of an integrated duration of ~40 million years, with each event lasting ≥105 years, consistent with the formation timescale of valley networks. Declining atmospheric CO2 via surface oxidant sinks or variations in the planet’s axial tilt could have led to abrupt shifts in the planet’s redox state and transition to a CO-dominated atmosphere and cold climate.

1701物理及び化学
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