The structure, stability, and global distribution of Io's atmosphere
The structure, stability, and global distribution of Io's atmosphere
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艾奥大气层的结构、稳定性和全球分布
DOI：
10.1016/0019-1035(92)90095-o
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发表时间：
1992
期刊：
影响因子：
3.2
通讯作者：
T. Encrenaz
中科院分区：
文献类型：
--
作者：
E. Lellouch;M. Belton;I. Pater;G. Paubert;S. Gulkis;T. Encrenaz
对二氧化硫的毫米波观测首次实现了对木卫一中性大气层的地面直接探测。从观测的两个SO2旋转线，在221.965和143.057 GHz，试探性检测的第三个SO2线，在346.652 GHz，和上限的其他两条线，木卫一的大气的基本属性进行推断。SO 2的大气层似乎具有全球性的时间稳定性，可以用厚度为1011− 1012 cm − 3（p = 3−40 nbar）的碰撞大气层来表示，它覆盖了木卫一表面的有限部分（5-20%），尾部的压力可能比头部大。气态SO2的水平分布最好描述为（平衡或火山）源的离散分布的结果，而不是通过表面霜的平滑分布上的蒸汽压平衡。低层大气似乎出奇地热，在40公里处约为500-600 K。IRIS/Voyager对洛基上空7 μm处ν 3SO 2波段观测的再分析，使用NLTE传输模型，表明洛基的温度/压力条件与从毫米波数据导出的全球大气的温度/压力条件一致。然而，简单的热模型不能适应低尺度高度的高温。我们的研究结果表明，木卫一的大气可能是最好的描述了“火山源”的大气模型，虽然“平衡”模型的某些方面，特别是时间的稳定性，也存在。虽然首要的问题仍然是需要明确地确定和解释垂直热结构，但必须指出的是，如果大气是热的，那么大气与一个或多个火山源处于动力学平衡的概念可能会为先锋10号掩星提供合理的解释。最后，获得了大气中H2S、SO和CO的新上限。
Millimeter-wave observations of SO2have allowed the first groundbased direct detection of Io's neutral atmosphere. From observations of two SO2rotational lines, at 221.965 and 143.057 GHz, tentative detection of a third SO2line, at 346.652 GHz, and upper limits on two other lines, basic properties of Io's atmosphere are inferred. The SO2atmosphere appears to have global temporal stability and can be represented by a collisionally thick 1011−1012cm−3atmosphere (p = 3−40 nbar) covering a limited fraction (5–20%) of Io's surface, with possibly larger pressures on the trailing side than on the leading. The horizontal distribution of gaseous SO2is best described as the result of discrete distribution of (equilibrium or volcanic) sources rather than by vapor pressure equilibrium over a smooth distribution of surface frosts. The lower atmosphere seems surprisingly hot, about 500–600 K at 40 km. A reanalysis of the IRIS/Voyager observation of the ν3SO2band at 7 μm over Loki, using a NLTE transfer model, suggests temperature/pressure conditions at Loki consistent with those derived for the global atmosphere from the millimeter-wave data. High temperatures in the lower scale height, however, are not accommodated by simple thermal models. Our results suggest that Io's atmosphere may be best described by a “volcanic source” atmospheric model, although some aspects of the “equilibrium” models, notably the temporal stability, are also present. While the primary problem remains the need to unambigously determine and explain the vertical thermal structure, it must be noted that if the atmosphere is hot, the concept of an atmosphere in dynamical equilibrium with one or more volcanic sources may provide a reasonable explanation to the Pioneer 10 occultation. Finally, new upper limits on atmospheric H2S, SO, and CO were obtained.