水星钠逸散层中的冷极增强现象。
A Cold-Pole Enhancement in Mercury's Sodium Exosphere.
作者信息
Cassidy Timothy A, McClintock William E, Killen Rosemary M, Sarantos Menelaos, Merkel Aimee W, Vervack Ronald J, Burger Matthew H
机构信息
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA.
Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
出版信息
Geophys Res Lett. 2016 Nov 16;43(21):12111-11128. doi: 10.1002/2016GL071071. Epub 2016 Oct 23.
The Ultraviolet and Visible Spectrometer (UVVS) component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MESSENGER spacecraft characterized the local-time distribution of the sodium exosphere over the course of its orbital mission. The observations show that the sodium exosphere is enhanced above Mercury's cold-pole longitudes. Based on previously published sodium exosphere models we infer that these regions act as nightside surface reservoirs, temporary sinks to the exosphere that collect sodium atoms transported anti-sunward. The reservoirs are revealed as exospheric enhancements when they are exposed to sunlight. As in the models the reservoir is depleted as the cold poles rotate from dawn to dusk, but unlike the models the depletion is only partial. The persistence of the reservoir means that it could, over the course of geologically long periods of time, contribute to an increase in the bulk concentration of sodium near the cold-pole longitudes.
信使号航天器上的水星大气与表面成分光谱仪（MASCS）的紫外可见光谱仪（UVVS）组件，在其轨道任务过程中对钠逸散层的地方时分布进行了表征。观测结果表明，钠逸散层在水星冷极经度上方增强。基于此前发表的钠逸散层模型，我们推断这些区域充当夜侧表面储库，即逸散层的临时汇，收集向反太阳方向传输的钠原子。当这些储库暴露于阳光下时，会表现为逸散层增强。与模型情况一样，随着冷极从黎明旋转到黄昏，储库会被耗尽，但与模型不同的是，这种耗尽只是部分的。储库的持续存在意味着，在地质长时间尺度上，它可能导致冷极经度附近钠的总体浓度增加。
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