16:30 〜 16:45
[PPS05-10] Whistler-mode Waves observed during Mercury flybys by BepiColombo/Mio PWI
キーワード：水星、BepiColombo、Mio、プラズマ波動、波動粒子相互作用
The Plasma Wave Investigation (PWI) aboard BepiColombo/Mio spacecraft will deploy all sensors after the Mercury orbit insertion at the end of 2025. The full observational capabilities of electric fields, plasma waves, and radio waves enables the measurement of electron density and temperature, electromagnetic turbulences, and radio waves in and around the Hermean magnetosphere and exosphere, in the electric field from DC to 10 MHz along the spin plane and in the magnetic field from 0.3 Hz to 20 kHz in three-axis and from 2.5 kHz to 640 kHz in one-axis.
Unfortunately, during the cruising phase from its launch in 2018, long wire antennas (15-m x 4) for electric fields and the solid boom (4.5-m) for magnetic fields are not yet deployed. For electric field, one of the antenna pairs, WPT, is exposed to space, but with the length of few cm and grounded to the spacecraft body with several k-ohm. For magnetic field, the search-coils are active but under large noise environment from the spacecraft body. Although under such severe conditions, the PWI saw plasma waves around Mercury during the 1st, 2nd, and 3rd flybys (Oct. 2021, June 2022, and June 2023).
In this paper, we show the summary of ‘first historical detections of Hermean whistler wavess’ in the 1st and 2nd flybys (Ozaki+, 2023) with the results from the 3rd flyby. In the 1st and 2nd flybys, we saw magnetic field turbulences in several 10s kHz in the dawn side magnetosphere after the closest approach. It can be interrupted as the first whistler-wave detection. Whistler-mode chorus waves are natural electromagnetic emissions known to play a key role in electron acceleration and loss mechanisms via wave–particle interactions in planetary magnetospheres. Mio’s search coil magnetometers measured chorus waves with tens of pT in the dawn sector, while no clear wave activity was observed in the night sector. The simulation results suggest that this dawn-dusk asymmetry could be explained by the impact of background magnetic field inhomogeneities on the nonlinear wave generation process.
In the 1st and 2nd flybys the BepiColombo orbit is not close to the magnetic equator, but the 3rd flyby seems just there. Potential direct comparisons with electron data will be discussed using this data, in or close to the source region of Whistler waves. We will also report the current status of the data production plans, which will be used in the real start of the Hermean observation from 2026.
Unfortunately, during the cruising phase from its launch in 2018, long wire antennas (15-m x 4) for electric fields and the solid boom (4.5-m) for magnetic fields are not yet deployed. For electric field, one of the antenna pairs, WPT, is exposed to space, but with the length of few cm and grounded to the spacecraft body with several k-ohm. For magnetic field, the search-coils are active but under large noise environment from the spacecraft body. Although under such severe conditions, the PWI saw plasma waves around Mercury during the 1st, 2nd, and 3rd flybys (Oct. 2021, June 2022, and June 2023).
In this paper, we show the summary of ‘first historical detections of Hermean whistler wavess’ in the 1st and 2nd flybys (Ozaki+, 2023) with the results from the 3rd flyby. In the 1st and 2nd flybys, we saw magnetic field turbulences in several 10s kHz in the dawn side magnetosphere after the closest approach. It can be interrupted as the first whistler-wave detection. Whistler-mode chorus waves are natural electromagnetic emissions known to play a key role in electron acceleration and loss mechanisms via wave–particle interactions in planetary magnetospheres. Mio’s search coil magnetometers measured chorus waves with tens of pT in the dawn sector, while no clear wave activity was observed in the night sector. The simulation results suggest that this dawn-dusk asymmetry could be explained by the impact of background magnetic field inhomogeneities on the nonlinear wave generation process.
In the 1st and 2nd flybys the BepiColombo orbit is not close to the magnetic equator, but the 3rd flyby seems just there. Potential direct comparisons with electron data will be discussed using this data, in or close to the source region of Whistler waves. We will also report the current status of the data production plans, which will be used in the real start of the Hermean observation from 2026.