15:00 〜 15:15
[PPS09-18] Magnetotail Resonance as a Driver of Nighttime Magnetic Pulsations on Mars
キーワード：Surface magneetic field, InSight Mars lander, Magnetic pulsations, ULF waves, Induced magnetotail, Resonance
One of the most unexpected discoveries made by the InSight Flux Gate (IFG) magnetometer on the surface of Mars is the presence of quasi-sinusoidal magnetic pulsations observed around local midnight. This class of pulsations exhibits the narrowest bandwidth in the IFG wave spectra, with wave periods centered around 80–100 seconds. The source of these oscillations is most likely the induced Martian magnetotail, where the MAVEN spacecraft has detected compressional oscillations at similar frequencies. However, the exact generation mechanism remains unclear, partly because no direct counterpart of this phenomenon exists on Earth.
This study proposes that magnetotail resonance is the source of these quasi-sinusoidal nighttime magnetic pulsations on Mars, with the energy originating from solar wind perturbations and becoming trapped within the tail region. Because Mars lacks an intrinsic magnetosphere, magnetic perturbations in the tail can propagate through the ionosphere and reach the surface with minimal attenuation. Using statistical analyses of magnetic field and plasma data collected by MAVEN, I estimate the eigenperiods of the tail and plasma sheet modes. I find that the fundamental mode of the tail has a median wave period of approximately 100 seconds, which best matches the IFG observations of midnight pulsations. In contrast, the fundamental mode of the plasma sheet has a median period of roughly 20 seconds, making it a less likely wave source. Since frequency is one of the key parameters for identifying wave origins, these results strongly support the hypothesis that resonance in the induced magnetotail is responsible for the nighttime magnetic pulsations observed on the Martian surface.
This study proposes that magnetotail resonance is the source of these quasi-sinusoidal nighttime magnetic pulsations on Mars, with the energy originating from solar wind perturbations and becoming trapped within the tail region. Because Mars lacks an intrinsic magnetosphere, magnetic perturbations in the tail can propagate through the ionosphere and reach the surface with minimal attenuation. Using statistical analyses of magnetic field and plasma data collected by MAVEN, I estimate the eigenperiods of the tail and plasma sheet modes. I find that the fundamental mode of the tail has a median wave period of approximately 100 seconds, which best matches the IFG observations of midnight pulsations. In contrast, the fundamental mode of the plasma sheet has a median period of roughly 20 seconds, making it a less likely wave source. Since frequency is one of the key parameters for identifying wave origins, these results strongly support the hypothesis that resonance in the induced magnetotail is responsible for the nighttime magnetic pulsations observed on the Martian surface.