A Thermospheric Circulation Model for Extrasolar Giant Planets
A Thermospheric Circulation Model for Extrasolar Giant Planets
复制标题
太阳系外巨行星的热层环流模型
DOI：
10.1086/513594
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
S. Miller
中科院分区：
文献类型：
--
作者：
T. Koskinen;A. Aylward;C. Smith;S. Miller
近年来，几种太阳系外巨行星（EGP）大气的模型已经发展起来。其中许多是一维的，或者集中在低层或中层大气。三维流体动力学模式需要研究EGP大气的温度和成分的水平变化。高层大气的环流模式是特别重要的，因为它们可以用来研究由于恒星辐射，辐射冷却和大气环流的热结构在热层的近在EGP，因此其大气的蒸发率。我们提出了一个通用的气体巨星模型，能够产生三维的，自洽的全球模拟稳定的EGP热层在不同的轨道距离。该模型的计算结果表明，H离子的红外辐射在冷却距太阳型主星星至少0.2-1 Au范围内的EGP热层中起着重要作用。在此范围内，H2的热解离可以忽略不计，并且与总中性密度相比，离子密度较小。在0.2 Au以内，H2的热解离和解离光电离可能阻止H的有效形成。在没有来自H的辐射冷却的情况下，高层大气在~0.5 Au内达到远高于10，000 K的温度。在这种情况下，上层热层完全转化为原子氢，温度高到足以发生重大的大气损失。我们的模型是能够计算的红外信号强度的各种振动跃迁的H的基础上的热状态和大气的组成。因此，对这些信号的潜在检测将为我们的一些结果提供验证。
Several models of extrasolar giant planet (EGP) atmospheres have been developed recently. Many of them are one-dimensional or concentrate on the lower or middle atmosphere. Three-dimensional hydrodynamic models are needed to study the horizontal variations in temperature and composition of EGP atmospheres. Circulation models for the upper atmosphere are particularly important as they can be used to study the thermal structure due to stellar irradiation, radiative cooling, and atmospheric circulation in the thermospheres of close-in EGPs and hence the rate of evaporation of their atmospheres. We present a generic gas giant model that is capable of generating three-dimensional, self-consistent global simulations of stable EGP thermospheres at different orbital distances. Calculations performed by this model indicate that IR emissions from H ions may play a significant role in cooling the thermospheres of EGPs at least in the range of 0.2-1 AU from a solar-type host star. In this range thermal dissociation of H2 is negligible and ion densities are small compared to the overall neutral density. Inside 0.2 AU thermal dissociation and dissociative photoionization of H2 may prevent the effective formation of H. In the absence of radiative cooling from H the upper atmospheres reach temperatures well above 10,000 K within ~0.5 AU. In this case the upper thermospheres are entirely converted into atomic hydrogen and the temperatures are high enough for significant atmospheric loss to take place. Our model is capable of calculating the IR signal strengths for various vibrational transitions of H based on the thermal state and the composition of the atmosphere. Potential detection of such signals would thus provide a validation of some of our results.