We describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA’s Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk.
Dynamical evolution of paired asteroids sharing close orbits was investigated. Candidates were chosen from AstDyS database by Kholshevnikov metric value. Only 33 of 105 pairs with close orbits were associated as family members. Further orbit evolution modeling was performed by Orbit9 software. Each pair had 49 overall model scenarios due to different Yarkovsky drift values for semimajor axis. Close encounters between paired objects providing time estimations and feasible mechanisms of formation were evaluated. Uncertainties of Yarkovsky drift values affected orbit evolution and caused substantial distinctions in time formation evaluating. Dwarf planet Ceres and massive asteroids (Pallas, Vesta, etc.) perturbations should be taken into account and dynamical evolution research for asteroid pairs in close orbits under passing through resonances is considered in future numerical simulations.
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