11:15 AM - 11:30 AM
[PPS06-13] Analytical estimation of the origin of C-type asteroids through scattering of planetesimals by outward-migrating giant planets
Keywords:Planetary formation theory, Protoplanetary disk, C-type asteroids, Planetary migration
Hayabusa2 mission revealed that the samples from C–type asteroid Ryugu contains carbonate minerals and CO2-rich fluid inclusions (Nakamura et al., 2021), which implies the parent body of them have probably come from outside the CO2 snowline to the main asteroid belt through gravitational scattering by giant planets. Using orbital simulations, Raymond & Izidoro (2017) investigated the orbital evolution of icy planetesimals originating beyond Saturn, through the scattering by the growing and migrating giant planets and the gas drag from the dissipating protoplanetary disk. They showed that a significant fraction of planetesimals moved from the outer Solar System beyond the giant planets to the main belt, owing to the migration of Jupiter and Saturn based on the so-called Grand Tack model. However, recently the Grand Tack model has been questioned by Tanaka (2023), due to the excessive growth of Saturn. Therefore, we consider the possibility that the transport of icy planetesimals was driven mainly by the outward migration of Saturn and the ice giants, rather than by Jupiter. Nesvorný, et al. (2024) investigated the implantation fraction of icy planetesimals to the main belt for inward-migrating ice giants, where there is no clear evidence in the current solar system. Thus, this study aims for a scenario in which ice giants, formed further inward than their current orbits, grow and migrate outward. We performed large-scale orbital calculations of icy planetesimals using a supercomputer, to discuss the dependence of the migration rate of icy planetesimals to the main belt and the further inner region (the terrestrial region), on planetary growth and migration as well as the gas dissipation. The goal of this study is to estimate the range of models for the evolution of the early solar system.
As for the condition of planetary growth and migration, we set τJ, the time when Jupiter growth ends, as a parameter. The growth and migration times of each planet are linked to τJ, so that growth and migration occurs from the inner planets outward (however, migration of Jupiter is not considered). The disk gas dissipates due to viscous accretion, which decreases exponentially (with a characteristic timescale of τg, corresponding to the time when the gas reduces to 1/e of its initial value). The gas then disappears due to photoevaporation by solar X-rays (at a timescale denoted as τPE).
In the case of standard X-ray radiation (τJ=τg=0.8 Myr, τPE=3.2τg =2.56 Myr), icy planetesimals are more distributed in the inner main belt (1.8–2.5 au) and the terrestrial region than in the outer main belt (2.5–3.2 au) (Fig.1). Orbital analysis shows that most of the icy planetesimals, whose orbits were once stabilized in the outer main belt, had their eccentricity excited due to the secular resonance of Saturn, which moves inward in response to gas dissipation, and then migrated inward due to the gas drag. This result is inconsistent with the current orbital distribution of C–type asteroids, as they are abundant in the present outer main belt. When X-ray radiation is stronger (τPE=2τg =1.6 Myr), the effect of secular resonance becomes smaller. Furthermore, when the dispersal of the gas disk is slower, (τg=1.5τJ, 2τJ), the migration rate to the entire main belt tends to increase. However, it is unrealistic for the gas disk to persist for an excessively long period, considering the growth timescale of Jupiter and Saturn.
In the presentation, we will discuss the constraints on the evolution of the Solar System based on the migration rate of icy planetesimals, including calculations that vary the conditions for planetary growth and migration.
As for the condition of planetary growth and migration, we set τJ, the time when Jupiter growth ends, as a parameter. The growth and migration times of each planet are linked to τJ, so that growth and migration occurs from the inner planets outward (however, migration of Jupiter is not considered). The disk gas dissipates due to viscous accretion, which decreases exponentially (with a characteristic timescale of τg, corresponding to the time when the gas reduces to 1/e of its initial value). The gas then disappears due to photoevaporation by solar X-rays (at a timescale denoted as τPE).
In the case of standard X-ray radiation (τJ=τg=0.8 Myr, τPE=3.2τg =2.56 Myr), icy planetesimals are more distributed in the inner main belt (1.8–2.5 au) and the terrestrial region than in the outer main belt (2.5–3.2 au) (Fig.1). Orbital analysis shows that most of the icy planetesimals, whose orbits were once stabilized in the outer main belt, had their eccentricity excited due to the secular resonance of Saturn, which moves inward in response to gas dissipation, and then migrated inward due to the gas drag. This result is inconsistent with the current orbital distribution of C–type asteroids, as they are abundant in the present outer main belt. When X-ray radiation is stronger (τPE=2τg =1.6 Myr), the effect of secular resonance becomes smaller. Furthermore, when the dispersal of the gas disk is slower, (τg=1.5τJ, 2τJ), the migration rate to the entire main belt tends to increase. However, it is unrealistic for the gas disk to persist for an excessively long period, considering the growth timescale of Jupiter and Saturn.
In the presentation, we will discuss the constraints on the evolution of the Solar System based on the migration rate of icy planetesimals, including calculations that vary the conditions for planetary growth and migration.