热驱动大气逃逸
Thermally-Diven Atmospheric Escape
摘要：
准确地确定行星大气层的逃逸率对于确定其演化至关重要。逃逸可以由沉积在外底以下的能量的向上热传导驱动，也可以由沉积在外底区域的能量产生的非热过程驱动。最近应用的逃逸模型驱动向上的热传导，称为慢流体动力逃逸模型，导致了令人惊讶的大的损失率厚的土卫六，土星最大的卫星的大气。基于外碱基区域的分子动力学模拟，这些速率似乎是太大的数量级。由于卡西尼号已经获得了泰坦高层大气的大量数据，以及未来十年内冥王星、火星和太阳系外行星大气的大量数据，准确确定目前的逃逸率对于理解它们的演变至关重要。因此，本文对慢水动力学模型进行了评价。它表明，这样的模型不能给出一个可靠的描述大气温度分布，除非它是耦合到一个分子动力学描述的外基区。因此，必须使用本文描述的大气模型重新评估土卫六和冥王星目前的逃逸率。
英文摘要：
Accurately determining escape rates from a planet's atmosphere is critical for determining its evolution. Escape can be driven by upward thermal conduction of energy deposited well below the exobase, as well as by non-thermal processes produced by energy deposited in the exobase region. Recent applications of a model for escape driven by upward thermal conduction, called the slow hydrodynamic escape model, have resulted in surprisingly large loss rates for the thick atmosphere of Titan, Saturn's largest moon. Based on a molecular kinetic simulation of the exobase region, these rates appear to be orders of magnitude too large. Because of the large amount of Cassini data already available for Titan's upper atmosphere and the wealth of data expected within the next decade for the atmospheres of Pluto, Mars, and extrasolar planets, accurately determining present escape rates is critical for understanding their evolution. Therefore, the slow hydrodynamic model is evaluated here. It is shown that such a model cannot give a reliable description of the atmospheric temperature profile unless it is coupled to a molecular kinetic description of the exobase region. Therefore, the present escape rates for Titan and Pluto must be re-evaluated using atmospheric models described in this paper.
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