講演情報
[PPS01-P22]Feasibility Study of Zodiacal Light and Extragalactic Background Light Observations During the Cruise Phase of OPENS-0
*瀧本 幸司1、松浦 周二2、津村 耕司3、佐野 圭4、高橋 葵1、Michael Zemcov5、Andrew Poppe6、矢野 創1、坂谷 尚哉1、今村 剛7、芝池 諭人8、河原 創1、船瀬 龍1、尾崎 直哉1、徳永 翔1、久保 勇貴9 (1.宇宙航空研究開発機構宇宙科学研究所、2.関西学院大学、3.東京都市大学、4.九州工業大学、5.ロチェスター工科大学、6.カリフォルニア大学バークレー校、7.東京大学、8.鹿児島大学、9.神戸大学)
キーワード：
黄道光、銀河系外背景光、惑星間塵、土星、外惑星探査小型実験機
Zodiacal light (ZL), produced by sunlight scattered by interplanetary dust particles, is the dominant source of diffuse foreground emission in the visible and near-infrared sky observed from near-Earth space. The intensity, spatial distribution, and polarization properties of the ZL reflect the physical characteristics of interplanetary dust and its distribution in the inner solar system. At the same time, ZL represents the largest foreground obstacle to accurate measurements of the extragalactic background light (EBL), which encodes integrated information on galaxy formation and cosmic star formation history. A comprehensive understanding of both ZL and EBL therefore requires observations that characterize the foreground emission while minimizing its impact on fainter background components.
Most previous measurements of diffuse background light have been conducted from near-Earth environments, where the brightness and spatial structure of the ZL introduce significant systematic uncertainties. Observations at larger heliocentric distances provide an opportunity not only to improve the reliability of EBL measurements but also to investigate the structure and origin of interplanetary dust over a wider heliocentric range. In particular, measurements obtained while traversing the main asteroid belt may probe dust bands associated with specific asteroid families and allow comparison with infrared dust-band structures identified by earlier space missions. Furthermore, observations beyond the region where Jupiter-family comet (JFC) dust is thought to dominate may constrain the relative contributions of cometary dust, Kuiper Belt dust, and interstellar dust to the zodiacal cloud, thereby testing models of dust supply and transport.
The OPENS (Outer Planet Exploration by Novel Small Spacecraft) program is a mission concept aimed at exploring the outer solar system using compact, cost-effective spacecraft. OPENS-0, the first mission in this program and a candidate for the JAXA Eco & Fast Class, is a technology demonstration mission targeting Saturn. During its interplanetary cruise phase, OPENS-0 is expected to conduct astronomical observations using its onboard multipurpose camera system.
In this study, we investigate the feasibility of observing ZL and EBL during the cruise phase using this camera system, with emphasis on physical characterization of the zodiacal dust cloud. Observation scenarios are examined by considering heliocentric distance, viewing geometry relative to the Sun and ecliptic plane, spacecraft attitude constraints, detector characteristics, and stray-light conditions. The expected reduction in ZL brightness with increasing distance and its impact on photometric sensitivity are discussed, together with possible variations in brightness and polarization along the trajectory.
In addition to total intensity measurements, we explore the potential for polarization observations enabled by optional polarization modes. Since ZL exhibits characteristic polarization signatures arising from dust scattering, polarization measurements can constrain dust properties, scattering phase functions, and particle size distributions, and may help distinguish different dust populations. Possible correlations between remote-sensing ZL measurements and in situ dust counter data are also examined to link optical scattering properties with particle flux along the cruise trajectory.
By combining intensity and polarization measurements at multiple heliocentric distances with dust counter observations, OPENS-0 may enable comparative studies of the spatial structure, source contributions, and radial evolution of the zodiacal dust cloud from the inner to outer solar system. While improved foreground characterization will benefit future EBL studies, the primary focus of this feasibility study is to assess the potential of cruise-phase observations to advance understanding of interplanetary dust physics.
Most previous measurements of diffuse background light have been conducted from near-Earth environments, where the brightness and spatial structure of the ZL introduce significant systematic uncertainties. Observations at larger heliocentric distances provide an opportunity not only to improve the reliability of EBL measurements but also to investigate the structure and origin of interplanetary dust over a wider heliocentric range. In particular, measurements obtained while traversing the main asteroid belt may probe dust bands associated with specific asteroid families and allow comparison with infrared dust-band structures identified by earlier space missions. Furthermore, observations beyond the region where Jupiter-family comet (JFC) dust is thought to dominate may constrain the relative contributions of cometary dust, Kuiper Belt dust, and interstellar dust to the zodiacal cloud, thereby testing models of dust supply and transport.
The OPENS (Outer Planet Exploration by Novel Small Spacecraft) program is a mission concept aimed at exploring the outer solar system using compact, cost-effective spacecraft. OPENS-0, the first mission in this program and a candidate for the JAXA Eco & Fast Class, is a technology demonstration mission targeting Saturn. During its interplanetary cruise phase, OPENS-0 is expected to conduct astronomical observations using its onboard multipurpose camera system.
In this study, we investigate the feasibility of observing ZL and EBL during the cruise phase using this camera system, with emphasis on physical characterization of the zodiacal dust cloud. Observation scenarios are examined by considering heliocentric distance, viewing geometry relative to the Sun and ecliptic plane, spacecraft attitude constraints, detector characteristics, and stray-light conditions. The expected reduction in ZL brightness with increasing distance and its impact on photometric sensitivity are discussed, together with possible variations in brightness and polarization along the trajectory.
In addition to total intensity measurements, we explore the potential for polarization observations enabled by optional polarization modes. Since ZL exhibits characteristic polarization signatures arising from dust scattering, polarization measurements can constrain dust properties, scattering phase functions, and particle size distributions, and may help distinguish different dust populations. Possible correlations between remote-sensing ZL measurements and in situ dust counter data are also examined to link optical scattering properties with particle flux along the cruise trajectory.
By combining intensity and polarization measurements at multiple heliocentric distances with dust counter observations, OPENS-0 may enable comparative studies of the spatial structure, source contributions, and radial evolution of the zodiacal dust cloud from the inner to outer solar system. While improved foreground characterization will benefit future EBL studies, the primary focus of this feasibility study is to assess the potential of cruise-phase observations to advance understanding of interplanetary dust physics.