科研之友
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摘要
Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars. Plain Language Summary We have extensive knowledge of metal ion layers in the Earth's ionosphere resulting from the atmospheric ablation of interplanetary dust particles. Understanding of potential ionospheric metals in other planetary atmospheres has been based primarily on our terrestrial understanding and the inference of their presence on other planets from radio occultation measurements of low-altitude electron density layers. The ion measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, now orbiting Mars, have now corroborated the continual presence of metal ion species in the Mars ionosphere. Further, these metal ion distributions are drastically different from those at Earth because the terrestrial ions are strongly affected by the Earth's intrinsic magnetic field, whereas Mars has no such field. Unique Mars metal ion structures have been encountered that have no counterpart in the Earth's ionosphere.
- 出版日期2017-4-16
