13:45 〜 14:00
[PAE18-13] Snow line migration in protoplanetary disks with various central stars and heating mechanisms: Implications for the water content of habitable planets
キーワード：原始惑星系円盤、スノーライン、ハビタブルゾーン、ハビタブル惑星
The question of whether habitable planets exist beyond Earth is one of the most significant topics in planetary science. One key concept in the search for habitable planets is the habitable zone (HZ; Kasting et al. 1993), which is defined as the orbital region where a planet can sustain liquid water on its surface. Planets located within this zone are expected to facilitate chemical reactions necessary for the emergence of life, as the presence of water generally promotes such reactions. However, an excessive amount of water on a planet may negatively impact the evolution of life. Thick ocean layers can create high-pressure environments that hinder plate tectonics and suppress essential chemical reactions due to the absence of land, potentially obstructing the emergence of life (e.g., Kite et al. 2009). Therefore, assessing the water content of planets within the HZ is crucial for the search for life.
Understanding the water content of planets requires knowledge of the snow line's location. The snow line is the orbital boundary in a protoplanetary disk where water ice sublimates. The snow line moves inward over time, impacting the amount of water delivered to planets in the HZ. Mulders et al. (2015) estimated the snow line's location based on heating due to turbulent viscosity in the disk and examined the amount of water transported by icy bodies to the HZ for M-dwarfs and solar-mass stars. However, stellar irradiation is the dominant disk heating mechanism in disks around M-dwarfs, which have lower disk masses. Additionally, recent studies suggest that the origin of disk turbulence remains uncertain, leading to the development of alternative models where Joule dissipation in the upper layers of the disk contributes to internal heating, independent of viscous heating (Mori et al. 2021; Kondo et al. 2023).
In this study, we investigate the relationship between the snow line and the HZ under different heating mechanisms and disk evolutionary processes, considering various types of central stars. We consider central stars of 0.1 and 1 solar masses, incorporating stellar luminosity evolution (Feiden 2016). We examine three heating scenarios: (1) stellar irradiation, (2) irradiation + viscous heating, and (3) irradiation + Joule heating from magnetohydrodynamic (MHD) processes in the disk. We compute the snow line’s migration using a model that simultaneously evolves the gas, temperature, and dust distributions—including dust growth and transport—within the disk (Kondo et al., in prep.) and compare its location with the HZ.
Our results indicate that internal disk heating is inefficient for low-mass stars. In the case of a 0.1 solar-mass star, the time at which the snow line reaches the inner edge of the HZ remains unchanged (> 10 Myr) regardless of whether viscous or Joule heating is included. In contrast, for a 1 solar-mass star, the contribution of internal heating delays the snow line’s arrival at the inner boundary of the HZ by approximately 2–3 Myr compared to the case of irradiation alone. Moreover, since the HZ eventually lies outside the snow line in a disk around a solar-mass star, our results suggest that planets within the HZ are more likely to acquire icy solid particles from the outer disk, leading to the formation of more water-rich planets.
Understanding the water content of planets requires knowledge of the snow line's location. The snow line is the orbital boundary in a protoplanetary disk where water ice sublimates. The snow line moves inward over time, impacting the amount of water delivered to planets in the HZ. Mulders et al. (2015) estimated the snow line's location based on heating due to turbulent viscosity in the disk and examined the amount of water transported by icy bodies to the HZ for M-dwarfs and solar-mass stars. However, stellar irradiation is the dominant disk heating mechanism in disks around M-dwarfs, which have lower disk masses. Additionally, recent studies suggest that the origin of disk turbulence remains uncertain, leading to the development of alternative models where Joule dissipation in the upper layers of the disk contributes to internal heating, independent of viscous heating (Mori et al. 2021; Kondo et al. 2023).
In this study, we investigate the relationship between the snow line and the HZ under different heating mechanisms and disk evolutionary processes, considering various types of central stars. We consider central stars of 0.1 and 1 solar masses, incorporating stellar luminosity evolution (Feiden 2016). We examine three heating scenarios: (1) stellar irradiation, (2) irradiation + viscous heating, and (3) irradiation + Joule heating from magnetohydrodynamic (MHD) processes in the disk. We compute the snow line’s migration using a model that simultaneously evolves the gas, temperature, and dust distributions—including dust growth and transport—within the disk (Kondo et al., in prep.) and compare its location with the HZ.
Our results indicate that internal disk heating is inefficient for low-mass stars. In the case of a 0.1 solar-mass star, the time at which the snow line reaches the inner edge of the HZ remains unchanged (> 10 Myr) regardless of whether viscous or Joule heating is included. In contrast, for a 1 solar-mass star, the contribution of internal heating delays the snow line’s arrival at the inner boundary of the HZ by approximately 2–3 Myr compared to the case of irradiation alone. Moreover, since the HZ eventually lies outside the snow line in a disk around a solar-mass star, our results suggest that planets within the HZ are more likely to acquire icy solid particles from the outer disk, leading to the formation of more water-rich planets.