3:00 PM - 3:15 PM
[PPS08-18] Carbon depletion problem of the inner solar system
The bulk Earth is depleted in carbon compared to the sun and dust in the interstellar medium (ISM). Asteroids are also thought to be depleted in carbon from the analysis of meteorites (e.g., Alexander et al. 2007). Carbon grains exist as refractory materials, such as amorphous carbons and refractory organics in the ISM and comets. Since these carbonaceous materials exist as solids near the earth's and asteroids' orbit, these rocky bodies would be more abundant in carbon if they had been formed from the solids whose composition is similar to that of the ISM and comets. In order to explain the carbon abundance of current rocky bodies, most of the refractory carbonaceous solids should be destroyed.
An experiment showed that amorphous carbons can be destroyed by far-ultraviolet (FUV) photolysis (Alata et al. 2014; 2015). Because the surface of a protoplanetary disk is exposed to FUV from the central star, the carbon solids could be destroyed enough when they are lifted to and remain in FUV-exposed layer (Anderson et al. 2017). However, considering the radial drift of solids, the carbon solids drift faster than they are destroyed by photolysis (Klarmann et al. 2018; Binkert & Birnstiel 2023). Therefore, previous studies concluded that the refractory carbon materials cannot be destroyed enough only by photolysis. However, while they assmued the constant stickiness of solids in the entire disk region, some experiments suggested that icy particles are more sticky than silicate particles. This condition might influence the dust compositon in the disk (Okamoto & Ida 2022).
In this study, we performed a 3D Monte Carlo simulation of particles' motion in the disk, assuming that the silicate particles are less sticky than icy particles, and stickiness of carbon solids is similar to silicate. As a result, carbon fraction started decreasing near the snow line. The carbon fraction dropped to ~0.01 there, and the lower carbon fraction extended to inner disk region. This distribution is consistent with the carbon abundance of meteorites although it is still higher than that of the bulk earth. In order to explain the value of the earth, we have to consider other processes to carbon destraction, such as oxidation of the amorphous carbons at higher temperature ( T > 1200 K).
An experiment showed that amorphous carbons can be destroyed by far-ultraviolet (FUV) photolysis (Alata et al. 2014; 2015). Because the surface of a protoplanetary disk is exposed to FUV from the central star, the carbon solids could be destroyed enough when they are lifted to and remain in FUV-exposed layer (Anderson et al. 2017). However, considering the radial drift of solids, the carbon solids drift faster than they are destroyed by photolysis (Klarmann et al. 2018; Binkert & Birnstiel 2023). Therefore, previous studies concluded that the refractory carbon materials cannot be destroyed enough only by photolysis. However, while they assmued the constant stickiness of solids in the entire disk region, some experiments suggested that icy particles are more sticky than silicate particles. This condition might influence the dust compositon in the disk (Okamoto & Ida 2022).
In this study, we performed a 3D Monte Carlo simulation of particles' motion in the disk, assuming that the silicate particles are less sticky than icy particles, and stickiness of carbon solids is similar to silicate. As a result, carbon fraction started decreasing near the snow line. The carbon fraction dropped to ~0.01 there, and the lower carbon fraction extended to inner disk region. This distribution is consistent with the carbon abundance of meteorites although it is still higher than that of the bulk earth. In order to explain the value of the earth, we have to consider other processes to carbon destraction, such as oxidation of the amorphous carbons at higher temperature ( T > 1200 K).