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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Multispecies MHD Study of Ion Escape at Ancient Mars: Effects of an Intrinsic Magnetic Field and Solar XUV Radiation
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Multispecies MHD Study of Ion Escape at Ancient Mars: Effects of an Intrinsic Magnetic Field and Solar XUV Radiation

机译：古代火星离子逃逸的多物种MHD研究：固有磁场和太阳XUV辐射的影响

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摘要

Ion escape is one of the key processes responsible for drastic climate change on ancient Mars. Ion escape is affected by the solar X-ray and EUV (X-ray and extreme ultraviolet (XUV)) flux, the solar wind, and the presence of a planetary intrinsic magnetic field, all of which was much different at ancient Mars. We investigated how the presence and strength of a dipole field affects the ion escape under 50 or 10 times higher solar XUV flux and strong solar wind with multispecies magnetohydrodynamics model. The results showed two opposite effects on the escape rates, which is associated with the pressure ratio of the dipolar magnetic pressure at the equatorial surface to the solar wind dynamic pressure. The escape rates increase by up to a factor of 6 for O_2~+ and CO_2~+ but change little for O + if the pressure ratio is below 0.1. On the other hand, the escape rates decrease by more than one order of magnitude for the three ions if the pressure ratio is above 0.1. The threshold can be described by the pressure balance between the solar wind flow and the dipole field at high latitudes, where the ionospheric outflow emerges in the unmagnetized cases. The effects on the escape rates are stronger under lower solar XUV cases. The total escape rate reaches 10 27 s ?1 in the unmagnetized case, which may lead to a large contribution to atmospheric loss at ancient Mars, but it can be reduced by an order of magnitude in the presence of a dipole field.
机译：离子逃离的一个关键过程负责在古老的火星上剧烈的气候变化。受到太阳x射线和EUV逃跑(x射线和极端的紫外线(远紫外线)通量,太阳风,行星的存在固有磁场,所有的多不同于古代的火星。一个偶极子场的存在和力量影响离子逃离50岁以下或10倍太阳能远紫外线高通量和强烈的太阳风multispecies磁流体动力学模型。结果显示两种截然相反的影响逃跑率,这是与压力有关偶极磁压力的比例赤道表面太阳风动态压力。6倍成分~ +和二氧化碳~ +但改变对O +如果压力比低于0.1. 由三个不止一个数量级离子如果压力比高于0.1。阈值可以被描述的压力太阳风流动和平衡偶极子场高纬度地区,电离层流出出现在垂直入射用例。更强的降低太阳能远紫外线的情况下。逃逸速度达到10 27 s ? 1垂直入射情况下,这可能会导致一个大贡献在古代火星大气的损失,但它可以减少一个数量级一个偶极子场的存在。

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