[P-PS01] Outer Solar System Exploration Today, and Tomorrow

[PPS01-P05] Considering the icy satellites of the Solar system as analogs of potential life-harboring exomoons

*Balazs Bradak¹ (1.Kobe University, Faculty of Oceanology)

キーワード：Solar system, icy satellite, exomoon, gas giant

Despite the exponentially growing research interest and popularity of the icy satellites of gas and ice giants in the Solar system, sparked by the possibility of evolving life in their hidden oceans, there are still only a few studies using them as potential analogies in exomoon studies. The theory introduced here attempts to fill some part of such a hiatus by connecting the study of icy satellites and gas giants of the Solar and exoplanetary systems with potentially similar configurations. Considering i) the appearance of water in the Universe (age of the Universe: 0.3-0.4 Ga), ii) the beginning of the habitable cosmological epoch, in which life could evolve on planetary bodies (age of the Univ.: 10–17 Ma), and iii) the type of the earliest known planets (gas giants Psr B1620-26 B, age of the Univ.: 1.1 Ga; and WASP-183 b, age of the Univ.: 0.6 Ga or older), the study assume that, as an analogy to the Solar system, ancient icy satellites might orbit around those early gas giants, having subsurface oceans and harboring life. Based on such theory, exoplanets with putative icy exomoons with similar planetary characteristics like the ones in the Solar system were searched for in NASA's Exoplanet Archive. Factors, such as planetary radius and mass, orbital semi-major axis, location of the ice line, the maximum Saturn-analog distance from the ice line, the number of host stars, number of planets, spectral type (class G stars), and the stellar age of the host star were considered. Among the 5271 exoplanets, 11 candidate gas giants were found with more than one observed exoplanet in the system. Among the eleven candidates, five are in a star system, older than the Solar system (Fig. 1, bold names and black symbols), with only two systems comprise over two observed planets, namely HD 191939 and HD 34445 (Fig. 1). Considering the type of planets in the system, the similarity between the two candidates and the Solar system ends here. Both candidates comprise gas giants, transitional-type planets, and sub-Neptunes, but no Earth-like terrestrial and super-Earth types have been found there yet (Fig. 1). Despite the possible disappointment triggered by the expectation of more versatile planetary systems regarding the planet type, such preliminary result triggers further questions. The next step of the study will target the differences between the evolution of systems with similar astronomical characteristics, comprising a similar number of planets, but have significant differences in the configuration of planets, regarding the variation of planet types.