Planet のバックアップ(No.90)

惑星セミナー2022 †

惑星セミナーは原則として毎週木曜日の15:00から開催しています。（連絡係：伊藤祐一, 高橋実道，古家健次）
astro-phセミナーは毎週月曜日の12:00から開催しています。（連絡係：Chanoul Seo，瀧哲朗，松本侑士）

Schedule & History †

2021年度 2020年度 2019年度 2018年度 2017年度 2016年度 2015年度 2014年度

日程	発表	タイトル	Remarks	担当
前期第1回 4/14 15:00-	All members	Self-introduction		伊藤
前期第2回 4/28 15:00-	Masahiro Ikoma (NAOJ)	Five key questions answered via the analysis of 25 hot Jupiter atmospheres in eclipse		高橋
前期第3回 5/10 15:00-	Sho Shibata (University of Zurich)	Exploring formation pathways of gas giant planets using planetesimal accretion	Tuesday	古家
前期第4回 5/19 15:00-	Kenji Furuya (NAOJ)	Different degree of nitrogen and carbon depletion in protoplanetary disks		古家
前期第5回 6/2 15:00-	Tatsuya Yoshida (Tohoku University)	Hydrodynamic escape of reduced proto-atmospheres on Earth and Mars		伊藤
前期第X回 7/5 15:00-	Hidenori Genda (ELSI)	TBD	Tuesday	高橋

5/10 Sho Shibata (University of Zurich), Exploring formation pathways of gas giant planets using planetesimal accretion: The composition of gas giant planets is a useful tracer of planet formation. Recent observations of gas giant planets suggest that planetesimal accretion had occurred in their formation stage. In our previous studies, we found that large amount of planetesimals can be captured by a protoplanet when the protoplanet migrates into the region which we call as sweet spot for planetesimal accretion. In this talk, we will apply the theory of sweet spot to the formation of close-in gas giant planets and Jupiter and Saturn. We will discuss the formation history of those planets using the planetesimal accretion process.

6/2 Tatsuya Yoshida (Tohoku University), Hydrodynamic escape of reduced proto-atmospheres on Earth and Mars: Earth and Mars likely have obtained reduced proto-atmospheres enriched in H2 and CH4 through impact degassing from planetary building blocks and gravitational capture of the surrounding nebular gas during accretion. Such reduced proto-atmospheres are expected to have been lost by hydrodynamic escape, but their fluxes and timescale for hydrogen depletion remain highly uncertain due to the ambiguity in the radiative loss of energy and chemical processes in escaping outflows. Here we develop a one-dimensional hydrodynamic escape model which includes radiative and chemical processes for a multi-component atmosphere and applied to the reduced proto-atmospheres on Mars and Earth to estimate the atmospheric escape rates and propose possibly atmospheric evolutionary tracks that are consistent with the isotopic compositions and amounts of the surface volatiles. We find that the hydrodynamic escape is suppressed due to the energy loss by the radiative cooling both on Earth and Mars. The escape rate decreases more than one order of magnitude than that of the pure H2 atmosphere when the mixing ratio of CH4 is high. As a result, the duration of the reduced hydrogen-rich environment becomes longer, implying that the early atmospheres played important roles in producing organic matters linked to the emergence of living organisms. The suppression of the hydrodynamic escape by the radiative cooling is more significant on Earth due to the larger gravity and higher temperature in the escaping outflow. The difference in the hydrodynamic escape may have contributed to the difference in the amounts and isotopic compositions of the surface volatiles between Earth and Mars.