Analysis of Orbital Characteristics of Earth Resonant Returning and Non-resonant Returning Asteroids

During the long-term dynamical evolution, near-Earth asteroids can frequently undergo close encounters with Earth, posing potential threats to Earth’s safety. Based on their orbital resonance relationships with Earth, asteroids that experience multiple encounters during their orbital evolution can be classified into two categories: Earth-resonant returning asteroids and Earth non-resonant returning asteroids. Dynamically sensitive gravitational keyholes may exist near the orbits of these two types of asteroids, thereby offering a low-cost deflection strategy for planetary defense by utilizing weak perturbations. To gain a deeper understanding of the orbital characteristics of these two types of asteroids, a 100-year high-precision orbital integration was performed for virtual asteroids larger than 10 meters in size, based on the debiased orbit model for near-Earth asteroids, NEOMOD 3. All near-Earth encounter events less than 0.01 au occurring during this period were recorded. Based on these data, a power-law relationship between the annual frequency of near-Earth encounter events and the encounter distance was revealed, and it was found that the number of asteroids encountering Earth exhibits an approximate power-law decay characteristic with increasing encounter number. Furthermore, statistical analysis of orbital elements and encounter velocities indicates that the distributions of these parameters are significantly correlated with the number of encounters, and there are differences in the orbital distributions between resonant and non-resonant returning asteroids. Analysis shows that these differences stem from a “selection effect” of encounter frequency and encounter patterns on the orbits of near-Earth asteroids. The calculation results indicate that for a random near-Earth close-approach event, the probability that the corresponding asteroid had previously encountered Earth within 100 years, 50 years, and 20 years before the current event is approximately 13.7%, 2.98%, and 0.37%, respectively. This work can provide important theoretical and data support for research on dynamical characteristics of target asteroids in planetary defense and the design of low-cost defense missions.