太陽系科学研究系

村上 豪

ムラカミ ゴウ  (Go Murakami)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 助教

J-GLOBAL ID
201901001752900088
researchmap会員ID
B000359749

論文

 142
  • Yuki Harada, Yoshifumi Saito, Lina Z. Hadid, Dominique Delcourt, Sae Aizawa, Mathias Rojo, Nicolas André, Moa Persson, Markus Fraenz, Shoichiro Yokota, Andréi Fedorov, Wataru Miyake, Emmanuel Penou, Alain Barthe, Jean‐André Sauvaud, Bruno Katra, Shoya Matsuda, Go Murakami
    Journal of Geophysical Research: Space Physics 129(8) 2024年8月2日  
    Abstract Although solar wind‐driven convection is expected to dominate magnetospheric circulation at Mercury, its exact pattern remains poorly characterized by observations. Here we present BepiColombo Mio observations during the third Mercury flyby indicative of convection‐driven transport of low‐energy dense ions into the deep magnetosphere. During the flyby, Mio observed an energy‐dispersed ion population from the duskside magnetopause to the deep region of the midnight magnetosphere. A comparison of the observations with backward test particle simulations suggests that the observed energy dispersion structure can be explained in terms of energy‐selective transport by convection from the duskside tail magnetopause. We also discuss the properties and origins of more energetic ions observed in the more dipole‐like field regions of the magnetosphere in comparison to previously reported populations of the plasma sheet horn and ring current ions. Additionally, forward test particle simulations predict that most of the observed ions on the nightside will precipitate onto relatively low‐latitude regions of the nightside surface of Mercury for a typical convection case. The presented observations and simulation results reveal the critical role of magnetospheric convection in determining the structure of Mercury's magnetospheric plasma. The upstream driver dependence of magnetospheric convection and its effects on other magnetospheric processes and plasma‐surface interactions should be further investigated by in‐orbit BepiColombo observations.
  • M. Rojo, N. André, S. Aizawa, J.-A. Sauvaud, Y. Saito, Y. Harada, A. Fedorov, E. Penou, A. Barthe, M. Persson, S. Yokota, C. Mazelle, L. Z. Hadid, D. Delcourt, D. Fontaine, M. Fränz, B. Katra, N. Krupp, G. Murakami
    Astronomy & Astrophysics 687 A243-A243 2024年7月17日  
    Context. The Mercury electron analyzer (MEA) obtained new electron observations during the first three Mercury flybys by BepiColombo on October 1, 2021 (MFB1), June 23 , 2022 (MFB2), and June 19, 2023 (MFB3). BepiColombo entered the dusk side magnetotail from the flank magnetosheath in the northern hemisphere, crossed the Mercury solar orbital equator around midnight in the magnetotail, traveled from midnight to dawn in the southern hemisphere near the closest approach, and exited from the post-dawn magnetosphere into the dayside magnetosheath. Aims. We aim to identify the magnetospheric boundaries and describe the structure and dynamics of the electron populations observed in the various regions explored along the flyby trajectories. Methods. We derive 4s time resolution electron densities and temperatures from MEA observations. We compare and contrast our new BepiColombo electron observations with those obtained from the Mariner 10 scanning electron spectrometer (SES) 49 yr ago. Results. A comparison to the averaged magnetospheric boundary crossings of MESSENGER indicates that the magnetosphere of Mercury was compressed during MFB1, close to its average state during MFB2, and highly compressed during MFB3. Our new MEA observations reveal the presence of a wake effect very close behind Mercury when BepiColombo entered the shadow region, a significant dusk-dawn asymmetry in electron fluxes in the nightside magnetosphere, and strongly fluctuating electrons with energies above 100s eV in the dawnside magnetosphere. Magnetospheric electron densities and temperatures are in the range of 10–30 cm−3 and above a few 100s eV in the pre-midnight-sector, and in the range of 1–100 cm−3 and well below 100 eV in the post-midnight sector, respectively. Conclusions. The MEA electron observations of different solar wind properties encountered during the first three Mercury flybys reveal the highly dynamic response and variability of the solar wind-magnetosphere interactions at Mercury. A good match is found between the electron plasma parameters derived by MEA in the various regions of the Hermean environment and similar ones derived in a few cases from other instruments on board BepiColombo.
  • Hiroyasu Kondo, Fuminori Tsuchiya, Masato Kagitani, Shinnosuke Satoh, Hiroaki Misawa, Yuki Nakamura, Go Murakami, Tomoki Kimura, Atsushi Yamazaki, Ichiro Yoshikawa, Hajime Kita, Chihiro Tao
    2024年5月28日  
  • L. Z. Hadid, D. Delcourt, Y. Saito, M. Fränz, S. Yokota, B. Fiethe, C. Verdeil, B. Katra, F. Leblanc, H. Fischer, M. Persson, S. Aizawa, N. André, Y. Harada, A. Fedorov, D. Fontaine, N. Krupp, H. Michalik, J-J. Berthelier, H. Krüger, G. Murakami, S. Matsuda, D. Heyner, H.-U. Auster, I. Richter, J. Z. D. Mieth, D. Schmid, D. Fischer
    Nature Astronomy 2024年4月12日  査読有り
    Abstract On 10 August 2021, the Mercury-bound BepiColombo spacecraft performed its second fly-by of Venus and provided a short-lived observation of its induced magnetosphere. Here we report results recorded by the Mass Spectrum Analyzer on board Mio, which reveal the presence of cold O+ and C+ with an average total flux of ~4 ± 1 × 104 cm−2 s−1 at a distance of about six planetary radii in a region that has never been explored before. The ratio of escaping C+ to O+ is at most 0.31 ± 0.2, implying that, in addition to atomic O+ ions, CO group ions or water group ions may be a source of the observed O+. Simultaneous magnetometer observations suggest that these planetary ions were in the magnetosheath flank in the vicinity of the magnetic pileup boundary downstream. These results have important implications regarding the evolution of Venus’s atmosphere and, in particular, the evolution of water on the surface of the planet.
  • M. Rojo, M. Persson, J.-A. Sauvaud, S. Aizawa, G. Nicolaou, E. Penou, A. Barthe, N. André, C. Mazelle, A. Fedorov, S. Yokota, Y. Saito, D. Heyner, I. Richter, U. Auster, D. Schmid, D. Fischer, T. Horbury, C.J. Owen, M. Maksimovic, Y. Khotyaintsev, P. Louarn, G. Murakami
    Astronomy & Astrophysics 2024年3月11日  査読有り最終著者
    We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 A.U. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds.

MISC

 118
  • Fuminori Tsuchiya, Yasumasa Kasaba, Ichiro Yoshikawa, Go Murakami, Atsushi Yamazaki, Kazuo Yoshioka, Tomoki Kimura, Chihiro Tao, Ryoichi Koga, Hajime Kita, Kei Masunaga, Masato Kagitani, Shotaro Sakai, Masaki Kuwabara
    Abstract EGU 2023 2023年5月15日  招待有り
    Hisaki is an earth orbiting extreme ultraviolet spectroscope dedicated for observing solar system planets. Thanks to its monitoring capability, Hisaki has carried out unprecedented continuous observation of Io plasma torus, Jovian aurora, and Mars and Venus upper atmosphere since December 2013. One of notable phenomena observed by Hisaki is significant enhancements of neutral gas (sodium and oxygen) from Io occurred in the spring of 2015. Hisaki revealed that not only the plasma source, but transport, heating, and loss processes of magnetospheric plasma were influenced by the variation in the neutral source input. The presentation will include related topics from recent Hisaki publication. Since the autumn of 2016, the Juno spacecraft was in the orbit around Jupiter. Hisaki monitored activities of Jovian aurora and the plasma torus in the Juno era. These datasets will provide opportunities to compare in-situ observation by Juno with the global view by Hisaki. JAXA approved the Hisaki mission period by the end of March 2023. As a future remote observation platform, we are going to propose a UV space telescope, LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly), a Japanese-leading mission using heritages of UV instruments for planetary science (e.g., Hisaki) and space telescope techniques for astronomy. One of goals of this mission is dynamics of our solar system planets and moons as the most quantifiable archetypes of extraterrestrial habitable environments in the universe. Water plume that gushes from the subsurface ocean of Galilean moons and tenuous atmosphere which is generated by bombardment of energetic charged particles to the surface are primary targets of LAPYUTA. As the plume activity and the atmosphere are not stable, continuous monitoring with high spatial resolution is essential. The icy moon's plume and ambient space will be deeply explored with the spacecraft by NASA's and ESA's icy moon missions in 2020s-2030s. The complementary remote sensing by LAPYUTA will visualize their global structure and temporal dynamics.
  • Yudai Suzuki, Kazuo Yoshioka, Kei Masunaga, Hideyo Kawakita, Yoshiharu Shinnaka, Go Murakami, Tomoki Kimura, Fuminori Tsuchiya, Atsushi Yamazaki, Ichiro Yoshikawa
    2023年2月26日  
  • Kei Masunaga, Naoki Terada, Nao Yoshida, Yuki Nakamura, Takeshi Kuroda, Kazuo Yoshioka, Yudai Suzuki, Hiromu Nakagawa, Tomoki Kimura, Fuminori Tsuchiya, Go Murakami, Atsushi Yamazaki, Tomohiro Usui, Ichiro Yoshikawa
    2023年2月22日  
  • 今村 剛, 村上 豪, 岩井 一正, 三好 由純, 塩田 大幸
    日本惑星科学会誌遊星人 30(3) 105-106 2021年9月25日  
    2021年3月から4月にかけて,あかつきと水星探査機BepiColomboが地球から見て太陽のほぼ反対側を同時に通過する貴重な機会があり,これを活かして2 機が協調して太陽コロナの電波掩蔽観測を実施した.太陽観測衛星ひのでによる太陽表面の観測も同時に行い,コロナ研究のためのユニークなデータセットが得られた.
  • Kasaba Yasumasa, Takashima Takeshi, Matsuda Shoya, Eguchi Sadatoshi, Endo Manabu, Miyabara Takeshi, Taeda Masahiro, Kuroda Yoshikatsu, Kasahara Yoshiya, Imachi Tomohiko, Kojima Hirotsugu, Yagitani Satoshi, Moncuquet Michel, Wahlund Jan-Erik, Kumamoto Atsushi, Matsuoka Ayako, Baumjohann Wolfgang, Yokota Shoichiro, Asamura Kazushi, Saito Yoshifumi, Delcourt Dominique, Hirahara Masafumi, Barabash Stas, Andre Nicolas, Kobayashi Masanori, Yoshikawa Ichiro, Murakami Go, Hayakawa Hajime
    Space Science Reviews 216(3) 2020年  

共同研究・競争的資金等の研究課題

 11