科研之友
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摘要
The topside ionosphere of Mars is subject to dynamic interactions between the planet and the surrounding space environment. Significant variations in its structure have been observed that have not been consistently investigated or explained. All 5,600 ionospheric profiles obtained by the Mars Global Surveyor Radio Science experiment are analyzed here to systematically characterize a topside ionospheric layer that is visible in similar to 50% of the observations. For simplicity, we refer to this layer of plasma as the M3 layer and find that it is located, on average, similar to 40 km above the main ionospheric peak and reaches average maximum concentrations of similar to 9 x 10(3) cm(-3). The properties of this topside feature, derived from the Mars Global Surveyor (MGS) radio occultation data set, are compared with existing findings of topside plasma enhancements at Mars observed in other data sets. Newly found characteristics in the topside layer properties are shown to support that solar radiation is not the main production source of this layer, in contrast to the behavior expected for the lower ionospheric photochemical layers at Mars. The analysis presents a set of trends that must be explained by theory for the formation mechanisms. These trends do not support some popular explanations such as Kelvin-Helmholtz instabilities and crustal magnetic field localization. Occurrence rates suggest a more constant source, such precipitation from the solar wind, and possible subsequent heating. These findings shed light on the enigmatic behavior of the topside Martian ionosphere and its surrounding dynamics.
- 出版日期2018-1
