University of Colorado, Boulder, CO, USA.
NASA/Goddard Spaceflight Center, Greenbelt, MD, USA.
Science. 2017 Mar 31;355(6332):1408-1410. doi: 10.1126/science.aai7721.
The history of Mars' atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of Ar/Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars' atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today's cold, dry atmosphere.
火星大气的历史对于了解行星的地质演化和潜在宜居性非常重要。我们通过火星大气和挥发物演化（MAVEN）航天器对高层大气结构的测量来确定随着时间的推移流失到太空中的气体量。我们推导出 homopause 和 exobase 高度之间的 Ar/Ar 结构。由于通过吸积离子溅射将气体损失到太空中，氩发生了分馏，这优先去除了较轻的原子。测量结果表明，66%的大气氩已流失到太空中。因此，火星的大量大气气体已经流失到太空中，导致气候从早期温暖潮湿的环境过渡到今天寒冷干燥的大气。
