Trapped Ar isotopes in meteorite ALH 84001 indicate Mars did not have a thick ancient atmosphere

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• 作者：William S. Cassata ; David L. Shuster ; Paul R. Renne ; Benjamin P. Weiss
• 关键词：Mars ; Atmosphere ; Mars ; Climate ; Atmospheres ; Evolution ; Cosmochemistry
• 刊名：Icarus
• 出版年：2012
• 出版时间：September-October, 2012
• 年：2012
• 卷：221
• 期：1
• 页码：461-465
• 全文大小：311 K

文摘

Water is not currently stable in liquid form on the martian surface due to the present mean atmospheric pressure of ¡«7 mbar and mean global temperature of ¡«220 K. However, geomorphic features and hydrated mineral assemblages suggest that Mars¡¯ climate was once warmer and liquid water flowed on the surface. These observations may indicate a substantially more massive atmosphere in the past, but there have been few observational constraints on paleoatmospheric pressures. Here we show how the ⁴⁰Ar/³⁶Ar ratios of trapped gases within martian meteorite ALH 84001 constrain paleoatmospheric pressure on Mars during the Noachian era [¡«4.56-3.8 billion years (Ga)]. Our model indicates that atmospheric pressures did not exceed ¡«1.5 bar during the first 400 million years (Ma) of the Noachian era, and were <400 mbar by 4.16 Ga. Such pressures of CO₂ are only sufficient to stabilize liquid water on Mars¡¯ surface at low latitudes during seasonally warm periods. Other greenhouse gases like SO₂ and water vapor may have played an important role in intermittently stabilizing liquid water at higher latitudes following major volcanic eruptions or impact events.