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Last-modified: 2022-09-12 () 21:36:53 (23d)
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ߥʡϸ§Ȥ轵15:00鳫ŤƤޤϢƣ ʹ, ⶶ ƻŲ 򼡡
astro-phߥʡ轵12:00鳫ŤƤޤϢChanoul Seo ůϯ һΡ

Schedule & History

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

1 4/14 15:00-All membersSelf-introductionƣ
2 4/28 15:00-Masahiro Ikoma (NAOJ)Five key questions answered via the analysis of 25 hot Jupiter atmospheres in eclipse
3 5/10 15:00-Sho Shibata (University of Zurich)Exploring formation pathways of gas giant planets using planetesimal accretionTuesdayŲ
4 5/19 15:00-Kenji Furuya (NAOJ)Different degree of nitrogen and carbon depletion in protoplanetary disksŲ
5 6/2 15:00-Tatsuya Yoshida (Tohoku University)Hydrodynamic escape of reduced proto-atmospheres on Earth and Marsƣ
6 6/9 15:00-Tadahiro Kimura (University of Tokyo)ȾëǥΥӥ塼ʸۡ²ǥѤѡܸ
7 6/23 15:00-Tomohiro Yoshida (SOKENDAI/NAOJ)12CO/13CO Ratio in the TW Hya DiskŲ
8 7/5 15:00-Hidenori Genda (ELSI)Martian Moons eXploration (MMX) missionTuesday
9 7/14 15:00-Yuki Kanbara (University of Tokyo)ĬˤûAMDѤɾܸŲ
10 7/21 15:00-Daniel Koll (Peking University)The unusual climates of habitable sub-Neptunesƣ
11 7/28 15:00-Yasuhiro Hasegawa (JPL)Solid Accretion onto Neptune-Mass Planets: Constraints from the D/H ratio of Uranus and Neptune
X 10/14 13:00-Takuji Tsujimoto (NAOJ)TBAŲ
X 10/21 13:00-Hitoshi Miura (Nagoya City University)TBAƣ
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.
6/9 Tadahiro Kimura (University of Tokyo),ȾëǥΥӥ塼ʸۡ²ǥѤѡ
7/5 Hidenori Genda (ELSI), Martian Moons eXploration (MMX) mission
Mars has two small moons, Phobos and Deimos. Two leading hypotheses, "capture theory" and "giant impact theory," have been considered for their origin, but they have not been settled. JAXA plans the 3rd Japanese sample return mission called Martian Moon eXploration (MMX). MMX spacecraft explores the Martian moons and brings back regolith samples from Phobos to Earth in 2029. The sample analysis should reveal their origin, but why is the origin of tiny Martian moons so important? What grand story can we draw about the solar system from the samples of the tiny small moon? In this seminar, I will briefly introduce MMX mission, and explain why we chose tiny satellites orbiting Mars.
7/21 Daniel Koll (Peking University), The unusual climates of habitable sub-Neptunes
Sub-Neptune-sized exoplanets like K2-18b are one of the most common planets in our galaxy. These planets are highly promising targets to search nearby exoplanets for biosignatures, because some temperate sub-Neptunes could be hosting liquid H2O oceans underneath their H2 envelopes. The surface climates of H2-rich worlds remain poorly understood, however. In this talk I will first discuss the onset of the runaway greenhouse in a H2 atmosphere. Extending previous work by Nakajima, Ingersoll, and others on the runaway greenhouse, I will show how the unusual low mean-molecular-weight of H2 leads to a number of unique climate effects. Next, I will show that H2-rich atmospheres should also have unusually long sunsets, with atmospheric refraction and scattering extending the twilight zone far beyond that on Earth. Many questions still remain open about the climates of habitable sub-Neptunes, but better theoretical models combined with JWST observations should allow us to make rapid progress over the next couple of years.
7/28 Yasuhiro Hasegawa (JPL), Solid Accretion onto Neptune-Mass Planets: Constraints from the D/H ratio of Uranus and Neptune
The currently available, detailed properties (e.g., isotopic ratios) of solar system planets may provide guides for constructing better approaches of exoplanet characterization. With this motivation, we explore how the measured values of the deuterium-to-hydrogen (D/H) ratio of Uranus and Neptune can constrain their formation mechanisms. Under the assumption of in-situ formation, we investigate three solid accretion modes; a dominant accretion mode switches from pebble accretion to drag-enhanced three-body accretion and to canonical planetesimal accretion, as the solid radius increases. We consider a wide radius range of solids that are accreted onto (proto)Neptune-mass planets and compute the resulting accretion rates as a function of both the solid size and the solid surface density. We find that for small-sized solids, the rate becomes high enough to halt concurrent gas accretion, if all the solids have the same size. For large-sized solids, the solid surface density needs to be enhanced to accrete enough amounts of solids within the gas disk lifetime. We apply these accretion modes to the formation of Uranus and Neptune and show that if the minimum-mass solar nebula model is adopted, solids with radius of ~ 1 m to ~ 10 km should have contributed mainly to their deuterium enrichment; a tighter constraint can be derived if the full solid size distribution is determined. This work therefore demonstrates that the D/H ratio can be used as a tracer of solid accretion onto Neptune-mass planets. Similar efforts can be made for other atomic elements that serve as metallicity indicators.