Stellar magnetism, dynamo action and the solar-stellar connection
Allan Sacha Brun
Dept. of Astrophysics, CEA Paris-Saclay & Visiting professor at NAOJ
Solar-like stars are magnetic rotating objects that have a direct impact on their environment. Being able to understand the physical mechanisms behind such an intense magnetic activity is key. It is believe that dynamo action is the source of the magnetic field in solar-like stars and that there is a complex feedback loop between dynamo, rotation and braking by their wind along their secular evolution. By mean of high performance simulations we will discuss how such complex feedback loop comes about and summarise our current understanding of the magnetohydrodynamics of solar-like stars.
Place: 2F Conf. room（1236）
U.S-JAPAN collaboration on sample return missions
NASA Johnson Space Center
Volatile delivery to planets in habitable zones during planet formation
ELSI, Tokyo Institute of Technology
Degassed atmospheres of terrestrial planets are composed of volatile elements that condense only in outer, cold disk regions, such as N2, CO2, and H2O. Actually, the Earth is severely depleted in N and C compared to the Solar compositions, and H2O ocean mass is only 0.02 wt.% of the bulk Earth. Atmospheric molecules would have been delivered from the outer regions by some mechanisms such as scattering of volatile- bearing planetesimals by a giant planet(s), radial diffusion of the planetesimals due to mutual scattering, migrations of icy planets due to disk-planet interactions, or migrations of pebbles/planetesimals induced by gas drag during the disk evolution phase where the ice lines of the volatiles move inside of the terrestrial planet orbits. If H2O ices are not delivered to the terrestrial planets, water vapor atmosphere cannot exist. If organic materials are not delivered to the terrestrial planets, N2 or CO2 atmosphere cannot exist. In that case, the terrestrial planets cannot be "habitable" even if their orbits are well within the classical habitable zones. On the other hand, some fraction of H-He gas can also be captured by a terrestrial planet from the protoplanetary disk, if the planet becomes massive enough before the disk gas depletion. This capture also provides volatiles to the planet. Reaction of H in the gas can react with FeO in the magma ocean on the surface of the planet. Because H-He molecules are light, H-He atmosphere tends to escape from the planet on long timescales and heavier elements such as C and N can be dragged with the H-He flow. However, the atmosphere can also retain as main components of the atmosphere, depending on planetary mass and environments. The delivery and capture are determined by planet accretion process. Furthermore, reactions with magma ocean on early planetary surface can change the atmosphere amount and compositions a lot. In the case of pebble accretion, impact- generated magma oceans would not exist because accreting pebbles are decelerated or ablated by atmospheric gas drag. I will explain the current understanding of these issues and I want to discuss open problems.
Place: 2F Conf. room（1236）
The Architecture of Exoplanetary Systems
The basic geometry of the Solar System - the shapes, spacings, and orientations of the planetary orbits - has long been a subject of fascination as well as inspiration for planet-formation theories. For exoplanetary systems, those same properties have only recently come into focus. I will review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems. I will also discuss opportunities to improve our understanding with data from the upcoming TESS space mission.
Place: Shin-A 2F Conf room A （1257）