The time span and heliocentric distances of the snow line in the inner Solar System is the determining factor for the presence of volatiles. This project aims to provide a comprehensive analysis of HN3, CO2, and H2O snowline migration, considering different PPD evolution scenarios, and reveals the mechanisms governing the distribution of volatile species in PPD. Specifically, the project will focus on explore different disk gas accretion mechanisms, including classical viscous accretion and disk wind and test different fragmentation thresholds for different ices (Okuzumi & Tazaki., 2019); The applicant will simulate the particle sizes and accretion rate evolve on PPD with time accordingly for given dust stickiness and the angular momentum transport model (in collaboration with Prof. Okuzumi at Tokyo Tech). For each volatile species, the snowline is defined as the location where the partial pressure in the nebula gas equals the equilibrium vapor pressure, and considering the snowline of semi-volatile substances such as salts and clathrate (Poch et al., 2020).
The accurate determination of the amount of volatiles accreted by protoplanets need accurate simulation of the physical processes of accretion and disc evolution. This project aims to quantify the amount of multivolatile icy pebbles accreted by planetesimals (the 1st generation asteroids) after the migration of snowlines. This project primarily investigates the pebble accretion mode (Lambrechts & Johansen, 2012; Visser & Ormel, 2016), a mechanism in which the combined influences of gas drag and gravity enable the efficient accretion of small particles across a wide cross-section. By integrating the findings from Research A, which explore diverse disk conditions and pebble properties the applicant aims to quantitatively determine the abundance of volatile components involved in the process of planetesimal accretion.
The abundance of volatile components significantly impacting asteroids subsequent evolution since it determines the initial H2O-NH3-CO2 abundances of the asteroids thus influencing the subsequent aqueous alteration reactions to produce diverse secondary minerals (e.g., serpentine, ammoniated saponite, and carbonate). This project performs volatile-rock reaction experiments to predict secondary mineral compositions expected for different bulk volatile compositions (in collaboration with Prof. Komiya’s group at Univ. Tokyo). Specifically, aqueous rock-type experiments will be conducted under low-temperature hydrothermal and reducing conditions with initial volatile abundance reference to Research B on the content of planetesimal volatile components to investigate alteration processes and secondary mineral assemblages of chondrites in the earliest stages of alteration (Nomura and Miyamoto, 1998; Vacher et al. 2019; Kikuchi et al. 2021). The experiments will be conducted at 15-90°C for 1-720 days and the turn-out will be analyzed by X-ray diffraction, transmission electron microscope and compared with chemical equilibrium calculations (in collaboration with Dr. Shibuya at JAMSTEC).