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Föreläsare: Dr Yoshifumi Futaana
Datum och tid: 2004-12-09 10:00
Plats: Aniara
Energetic Neutral Atoms around Mars - Latest results from NPD onboard Mars Express
Energetic natural atoms (ENAs) around Mars are generated by interaction between the solar wind and the Martian exosphere. However, because the ENAs generated by the charge exchange of the solar wind protons have the same velocity as the solar wind flow, most of the ENAs are crashed into the Martian atmosphere. Several generation mechanisms of ENAs in space around Mars have been proposed. We devote our attention to the following two mechanisms: backscattered ENAs and subsolar ENAs.
The backscattered ENAs are generated at the top of the dayside exosphere, where the solar wind protons collide with the exospheric neutral particles and are scattered back as neutral atoms. The flux of the backscattered ENAs is expected to have solar zenith angle (SZA) dependence.
The subsolar ENAs are generated at around the subsolar point, where the solar wind flow is highly deflected from the Sun-Mars line. This means that a part of the deflected solar wind flow would experience charge-exchange and generated ENAs have different velocity of the undisturbed solar wind. The flow of the subsolar ENAs is expected to be an intense beam.
The Neutral Particle Detector (NPD) on board Mars Express obtains data around Mars from the beginning of this year (2004). We analyzed the data of NPD obtained in May and June and found the above-mentioned characteristics in the data. The observations and analysis are reported and the generation mechanisms of the Martian ENAs are discussed in this seminar.
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