PPARCセミナー (2022/10/21)

PPARCセミナー 2022/10/21

発表者: 安田陸人 (M2)
タイトル: Numerical radar simulation for the explorations of the ionosphere at Jupiter’s icy moons
アブスト: Jupiter’s icy moons such as Europa and Ganymede may harbor subsurface liquid water oceans. While only Earth has the ocean on the surface in the current solar system, multiple icy bodies like the icy moons of giant planets have oceans in their subsurface under the icy crust. So, the icy bodies are potentially more universal habitable environment than the Earth-type bodies. The icy bodies’ ionospheres include essential information for understanding the habitable environments because the ionospheres are formed as a result of the crusts’ weathering and putative water plumes from the subsurface oceans. Especially, the ionospheric structures and time variability reflect the activity of the crusts and oceans. However, the structures are still unclear because the ionospheric radio occultation and other effective explorations have difficulties of limited observing opportunities. So, we have been trying to uncover the structures by radar exploration, which will be connected to the explorations with the Radio & Plasma Wave Investigation (RPWI) and the Radar for Icy Moon Exploration (RIME) onboard the Jupiter ICy moons Explorer (JUICE). For future investigations of radio wave sounding with RPWI and RIME ranging in tens kHz to tens MHz, we have developed a numerical simulation code that models the propagation of electromagnetic (EM) waves and emulated occultation of the Jovian radio waves by the icy moon’s ionosphere during the flybys of the Galileo spacecraft to Jupiter’s icy moons. Here, we show the vertical ionospheric profiles using our numerical simulation code. We found that the maximum electron density is estimated at ~ 50 /cc in lower latitudes of Ganymede’s trailing hemisphere and ~ 150 /cc in higher latitudes of the leading hemisphere. We argue that these results reflect surface weathering due to magnetospheric particle bombardment. In this presentation, we will also indicate the ionospheric profiles of Callisto and discuss the generation processes of the profiles. As the next step, we plan to simulate the reflection and transmission of the EM waves in the icy crust and underlying ocean. By combining this new simulation with our current one for the ionospheres, the icy moon’s ionospheric and subsurface structures are expected to be elucidated. These simulations would also give constraints on the pressure and temperature of the subsurface, which finally lead to deep understanding of the icy moon’s habitability.

発表者: 吉野富士香 (M1)
タイトル: ハワイT60望遠鏡の補償光学系の開発状況
アブスト: ハワイのハレアカラ観測所にあるT60望遠鏡では、惑星大気の観測を継続的に行っている。T60のような地上望遠鏡では、大気の揺らぎの影響により空間分解能が制限されてしまうため、補償光学系が必要とされる。2019年に試験した補償光学系では、動作周波数が50Hzと低く、駆動ヒステリシスも大きかったため、ハードウェア・ソフトウェアを新たなものに変えた新システムを2022年3月よりT60に搭載している。現状、動作周波数は360Hzほどで、自然光での補償ループの収束も確認された。一方で、現状の制御法では、視野のエッジや副鏡部分の処理が難しい。そこで、新たにZernikeモード展開による波面の再構成と補正のシステムを組みこもうとしている。本発表では、T60補償光学系の開発状況を報告する。なお、この補償光学系は、現在開発中の口径1.8mのPLANETS望遠鏡にも応用される予定である。