Hydrogen and helium escape on Venus via energy transfer from hot oxygen atoms
Hydrogen and helium escape on Venus via energy transfer from hot oxygen atoms
复制标题
氢和氦通过热氧原子的能量转移在金星上逃逸
DOI：
10.1093/mnras/staa3744
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发表时间：
2020-12
影响因子：
4.8
通讯作者：
Jiang Yu
中科院分区：
文献类型：
--
作者：
Hao Gu;Jun Cui;D;an Niu;Jiang Yu
由于金星上的引力相对较强，重的大气中性粒子很难加速到逃逸速度。然而，多种过程，例如电离层 O$_2^+$ 的解离重组，能够产生热原子，从而向轻中性粒子传递大量能量并驱动其逃逸。在这项研究中，我们构建了一个蒙特卡罗模型来模拟金星上三种光物质 H、H2 和 He 通过这种连锁过程的大气逃逸。采用两种金星背景大气模型，适用于太阳最小和最大条件。我们的计算中使用了各种能量相关和物种相关的横截面，以及常见的强前向散射角分布。我们的模型结果表明，热 O 的撞击可能在驱动当前金星大气中总氢和氦逃逸方面发挥着主导作用，其中很大一部分来自外底线以下的区域。我们的计算还揭示了巨大的变化。特别令人感兴趣的是所有物种在高太阳活动时逃逸通量的减少模型，主要与高太阳活动时外底附近热氧浓度的增加有关，这阻碍了逃逸。最后，评估了由几个控制因素引起的模型不确定性，包括背景大气中相关光物质的分布、平面平行近似和有限 O 能量分布。
Due to the relatively strong gravity on Venus, heavy atmospheric neutrals are difficult to accelerate to the escape velocity. However, a variety of processes, such as the dissociative recombination of ionospheric O$_2^+$, are able to produce hot atoms which could deliver a significant amount of energy to light neutrals and drive their escape. In this study, we construct a Monte Carlo model to simulate atmospheric escape of three light species, H, H2, and He, on Venus via such a knock-on process. Two Venusian background atmosphere models are adopted, appropriate for solar minimum and maximum conditions. Various energy-dependent and species-dependent cross-sections, along with a common strongly forward scattering angle distribution, are used in our calculations. Our model results suggest that knock-on by hot O likely plays the dominant role in driving total atmospheric hydrogen and helium escape on Venus at the present epoch, with a significant portion contributed from regions below the exobase. Substantial variations are also revealed by our calculations. Of special interest is the modelled reduction in escape flux at high solar activities for all species, mainly associated with the enhancement in thermal O concentration near the exobase at high solar activities which hinders escape. Finally, model uncertainties due to several controlling factors, including the distribution of relevant light species in the background atmosphere, the plane-parallel approximation, and the finite O energy distribution, are evaluated.
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影响因子：
3.2
作者：
J. Fox;A. Hać
通讯作者：
J. Fox;A. Hać
影响因子：
5.2
作者：
Stefano Bovino;Peng Zhang;F. Gianturco;Alexander Dalgarno;V. Kharchenko
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影响因子：
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通讯作者：
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作者：
V. Krasnopolsky;G. Gladstone
通讯作者：
V. Krasnopolsky;G. Gladstone
影响因子：
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作者：
B. Shizgal
通讯作者：
B. Shizgal