土星赤道高层大气的能量沉积
Energy deposition in Saturn's equatorial upper atmosphere
摘要：
我们构建了土星赤道中性温度和H，H $_2$，He和CH $_4$的密度分布，在10 $^{-12}$和1 bar之间，使用卡西尼号的离子中性质谱仪（INMS）在2017年9月15日航天器最后一次进入土星大气层期间进行的测量，结合以前卡西尼复合红外光谱仪（CIRS）和紫外成像光谱仪（UVIS）的更深大气测量。这些中性的配置文件被送入能量沉积模型，采用软X射线和极紫外（EUV）太阳通量的光谱分辨率范围（$Δλ=4\times10^{-3}$ nm至1 nm）从TIMED/SEE，从SOHO/SUMER，从整个日光层间隔（WHI）安静的太阳活动组装。我们的能量沉积模型通过光电离和电子碰撞电离过程计算离子产生速率分布，以及CH $_4$的光解离速率。离子反应速率分布的测定对于获得准确的离子密度分布具有重要意义，而甲烷光解是引发复杂有机化学过程的关键。我们使用高分辨率H $_2$光吸收截面，它具有在800公里高度附近产生额外的电离峰的效果，评估在能量沉积模型的光谱分辨率的重要性。我们发现，这些峰仍然形成时，使用低分辨率（$Δλ=1$ nm）或中分辨率（$Δλ=0.1$ nm）的太阳光谱，只要高分辨率的截面包括在模型中。
英文摘要：
We construct Saturn equatorial neutral temperature and density profiles of H, H$_2$, He, and CH$_4$, between 10$^{-12}$ and 1 bar using measurements from Cassini's Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft's final plunge into Saturn's atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS). These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions ($Δλ=4\times10^{-3}$ nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH$_4$. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H$_2$ photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low-resolution ($Δλ=1$ nm) or mid-resolution ($Δλ=0.1$ nm) solar spectra, as long as high-resolution cross sections are included in the model.
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