PPARCセミナー (2025/04/21)

PPARCセミナー (2025/04/21)

(1)
[Name]
Fuminori Tsuchiya

[Title]
Current status of on going projects: LAPYUTA , etc.

[Abstract]
Current status of on going projects we are involving and action items in this year are presented. The projects I will show their overview of UV space telescope (LAPYUTA), Lunar low frequency radio observatory (TSUKUYOMI), Iitate planetary radio telescope (IPRT), and JUICE, but LAPYUTA will be introduced in detail at the seminar. LAPYUTA is an ultraviolet space telescope with four science objectives:  solar system objects, Earth-like exoplanet atmospheres, formation of nearby galaxies, the synthesis of heavy elements in universe. LAPYUTA will achieve ~100 times higher sensitivity and spatial resolution than HISAKI’s, enabling observations of ice satellites and the spatial structure of planetary atmospheres. LAPYUTA is currently undergoing technical and scientific studies in preparation for selection by JAXA in a few years’ time, and the progress of these studies will be presented.

現在進行形のプロジェクトの進捗と、今年度のタスクの話をします。概要紹介するプロジェクトは、主にLAPYUTA、月面天文台、IPRT、JUICEですが、セミナーではLAPYUTAについて詳しく紹介します。
LAPYUTAは紫外線の宇宙望遠鏡で、太陽系内の惑星に加え、地球型の系外惑星大気、近傍銀河、重力波源での重元素合成を４つの科学目標としています。「ひさき」は太陽系天体を追尾する性能を持つことによって惑星の長期連続観測を実現しましたが、LAPYUTAはこれにひさきの100倍の高い感度・空間分解能を追加して、氷衛星や惑星大気の空間構造の観測も可能とします。LAPYUTAは数年後のJAXAでの選定審査に向けた技術検討と科学検討をおこなっており、これらの進捗を紹介します。

(2)

[Name]

Rikuto Yasuda

[Title]
Ray Tracing for Titan’s Ionospheric Occultation of Saturn Radio Emissions: Implications for JUICE Mission

[Abstract]
Titan has an ionosphere with complex variations due to solar radiation and interactions with Saturn’s magnetosphere. Previous studies have investigated Titan’s electron density using methods such as radio occultation and in situ measurements (Garand et al., 2014; Chatain et al., 2021a, 2021b). Additional constraints on electron density are required for more detailed investigations.
In Yasuda et al. (2024), a new technique was developed to measure the electron densities of moons’ ionospheres using planetary auroral radio emissions. This technique was successfully applied to the Galileo PWS data of Jovian radio waves, revealing new insights into the electron densities and formation processes of the ionospheres of Ganymede and Callisto, both of which have tenuous neutral atmospheres.
To extend this method using radio emissions from other planets or to adapt it for moons with dense atmospheres, we applied it to the Cassini RPWS data to derive Titan’s ionospheric electron density. Our results demonstrate that Saturn’s radio emissions are refracted by Titan’s ionosphere, allowing us to measure the ionospheric electron density  from radio data. We also present the derived electron density profiles of Titan’s ionosphere during the Cassini Titan 15 flyby.
The Cassini RPWS observations provide the closest analog to the JUICE RPWI observations, which will provide not only the flux but also polarization measurements of the radio waves surrounding the outer planets’ icy moons.  Polarization measurements are crucial as they help constrain the location of radio sources and the total electron content of Saturn’s radio emissions. By applying our method to Cassini data, we can gain new insights that will contribute to future studies of icy moon ionospheres with JUICE RPWI.