Multispecies MHD study of ion escape at ancient Mars: Effects of an intrinsic magnetic field and solar XUV radiation
Multispecies MHD study of ion escape at ancient Mars: Effects of an intrinsic magnetic field and solar XUV radiation
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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
DOI：
10.1029/2022ja030427
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
T.
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文献类型：
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作者：
Sakata;R.;Seki;K.;Sakai;S.;Terada;N.;Shinagawa;H.;& Tanaka;T.
离子逃逸是造成古代火星剧烈气候变化的关键过程之一。离子逃逸受到太阳X射线和EUV（X射线和极紫外线（XUV））通量，太阳风以及行星内部磁场的影响，所有这些都与古代火星有很大不同。利用多物种磁流体动力学模型研究了在50倍或10倍太阳XUV通量和强太阳风条件下，偶极场的存在和强度对离子逃逸的影响。结果表明，逃逸率与赤道面偶极磁压和太阳风动压的压力比有关。逃逸率增加到6倍的O2+和CO2+，但变化不大的O+，如果压力比低于0.1。另一方面，如果压力比大于0.1，则三种离子的逃逸率降低一个数量级以上。该阈值可以用高纬度地区太阳风和偶极子场之间的压力平衡来描述，在高纬度地区，电离层外流在未磁化的情况下出现。在太阳XUV较低的情况下，对逃逸率的影响更强。在未磁化的情况下，总逃逸率达到1027 s − 1，这可能导致古代火星大气损失的巨大贡献，但在偶极场的存在下，它可以减少一个数量级。
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 O2+and CO2+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 1027s−1in 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.