11:15 AM - 11:30 AM
[MZZ40-09] Verification of the Non-Gravitational Effects on a Binary Asteroid with the Hera Mission
Keywords:Asteroid, Binary asteroid, Hera mission, Planetary defense, Yarkovsky effect, YORP effect
The planetary defense mission AIDA, consisting of the U.S. DART and European Hera missions, is ongoing. In September 2022, the DART spacecraft crushed into the satellite of a binary asteroid, Didymos. A change in the orbital period of the satellite Dimorphos has been observed (Daly et al., 2023). The next Hera mission will rendezvous with Didymos and Dimorphos in December 2026 to observe the artificial craters formed by DART in detail. A thermal infrared imager (TIRI) onboard the Hera spacecraft has been developed to constrain the thermophysical properties of the asteroid's surface, such as thermal inertia, porosity, and the degree of surface roughness.
An asteroid's orbital and rotational evolution is affected not only by gravity but also by pressure generated by thermal radiation, i.e., non-gravitational effects. Thermography by TIRI is expected to reveal the thermal radiation characteristics of the asteroid, which helps improve the prediction of the orbit of asteroids approaching Earth. We aim to develop a theory of non-gravitational effects acting on the binary asteroid and demonstrate it with the Hera mission.
The orbital evolution of the satellite of a binary asteroid is primarily driven by tide and binary YORP (BYORP). In most binary asteroids, the primary bodies are relatively fast rotators, and tidal evolution increases the semi-major axes of the satellites. On the other hand, the BYORP effect is a torque caused by thermal radiation from the satellite, which can increase or decrease the semi-major axis depending on its irregular shape (Ćuk and Burns, 2005). If the BYORP effect carries the satellite outward with tidal evolution, the binary asteroid will be separated from each other to become a split pair. If the outward tidal evolution is balanced with the inward BYORP drift, the binary asteroid will be stable over the long term.
We also consider the Yarkovsky-Schach effect acting on a binary asteroid, a type of perturbation due to thermal radiation that occurs in a system where the satellite enters the shadow of the primary body. It has been studied as a mechanism for the orbital evolution of Saturn's ring particles (Rubincam, 2006; Vokrouhlický et al., 2007). We model the Yarkovsky-Schach effect acting on the satellite of the binary asteroid in both analytical and numerical approaches. The results show that the satellite with frequent eclipses can evolve to a tidally locked orbit due to the Yarkovsky-Schach effect. This orbital evolution of the satellite has important implications for interpreting the statistics of binary asteroids.
An asteroid's orbital and rotational evolution is affected not only by gravity but also by pressure generated by thermal radiation, i.e., non-gravitational effects. Thermography by TIRI is expected to reveal the thermal radiation characteristics of the asteroid, which helps improve the prediction of the orbit of asteroids approaching Earth. We aim to develop a theory of non-gravitational effects acting on the binary asteroid and demonstrate it with the Hera mission.
The orbital evolution of the satellite of a binary asteroid is primarily driven by tide and binary YORP (BYORP). In most binary asteroids, the primary bodies are relatively fast rotators, and tidal evolution increases the semi-major axes of the satellites. On the other hand, the BYORP effect is a torque caused by thermal radiation from the satellite, which can increase or decrease the semi-major axis depending on its irregular shape (Ćuk and Burns, 2005). If the BYORP effect carries the satellite outward with tidal evolution, the binary asteroid will be separated from each other to become a split pair. If the outward tidal evolution is balanced with the inward BYORP drift, the binary asteroid will be stable over the long term.
We also consider the Yarkovsky-Schach effect acting on a binary asteroid, a type of perturbation due to thermal radiation that occurs in a system where the satellite enters the shadow of the primary body. It has been studied as a mechanism for the orbital evolution of Saturn's ring particles (Rubincam, 2006; Vokrouhlický et al., 2007). We model the Yarkovsky-Schach effect acting on the satellite of the binary asteroid in both analytical and numerical approaches. The results show that the satellite with frequent eclipses can evolve to a tidally locked orbit due to the Yarkovsky-Schach effect. This orbital evolution of the satellite has important implications for interpreting the statistics of binary asteroids.