14:00 〜 14:15
[PAE18-14] Orbital instabilities in compact planetary systems
キーワード：Exoplanets, Celestial Mechanics, Chaotic Dynamics
Compact protoplanet systems are a natural outcome of the runaway and oligarchic growth of planetesimals. In such systems, low-mass protoplanets orbit their central star with a mean orbital separation, $K = a_{i+1}-a_{i}$, on the order of 10 units of their mutual Hill radius, $R_{Hill}^{i+1,i}$, and can only further grow to Earth-like masses through giant impacts between the protoplanets.
On the other hand, observational data from the Kepler sample indicate that compact planetary systems around billion-year-old stars are not uncommon, with the orbital separation distribution of non-resonant systems clustering at $K>10R_{Hill}^{i, i+1}$ and spreading beyond.
While both compact protoplanet systems and Kepler multis share relatively small values of mutual orbital separation, the latter are commonly deemed stable due to their host star’s age, whereas the former commonly undergo instabilities on variable timescales.
Given this dichotomy, it is natural to ask whether the difference in stability between compact protoplanet systems and Kepler multis arises from their formation conditions or if it is a product of dynamical evolution. Understanding the typical instability timescales and their sensitivity to orbital and physical properties is crucial for constraining their long-term evolution and final architectures.
To address this, we numerically studied thousands of compact planetary systems with different orbital separations and evaluated their typical instability timescales with respect to inhomogeneities—such as non-uniform masses and orbital spacing—and different orbital parameters. Sets considering distinct initial eccentricities, mutual inclinations, and orbital angles were numerically integrated to observe their individual and collective effects on the general stability of the system.
Moreover, we analyzed the effects of the very definition of “instability” by comparing distinct instability triggers found in the literature for the same given set of initial conditions, such as orbit crossings, close encounters, and physical collisions for each of those parameter sets.
On the other hand, observational data from the Kepler sample indicate that compact planetary systems around billion-year-old stars are not uncommon, with the orbital separation distribution of non-resonant systems clustering at $K>10R_{Hill}^{i, i+1}$ and spreading beyond.
While both compact protoplanet systems and Kepler multis share relatively small values of mutual orbital separation, the latter are commonly deemed stable due to their host star’s age, whereas the former commonly undergo instabilities on variable timescales.
Given this dichotomy, it is natural to ask whether the difference in stability between compact protoplanet systems and Kepler multis arises from their formation conditions or if it is a product of dynamical evolution. Understanding the typical instability timescales and their sensitivity to orbital and physical properties is crucial for constraining their long-term evolution and final architectures.
To address this, we numerically studied thousands of compact planetary systems with different orbital separations and evaluated their typical instability timescales with respect to inhomogeneities—such as non-uniform masses and orbital spacing—and different orbital parameters. Sets considering distinct initial eccentricities, mutual inclinations, and orbital angles were numerically integrated to observe their individual and collective effects on the general stability of the system.
Moreover, we analyzed the effects of the very definition of “instability” by comparing distinct instability triggers found in the literature for the same given set of initial conditions, such as orbit crossings, close encounters, and physical collisions for each of those parameter sets.