[M-ZZ40] International initiatives and cooperation in planetary defense

[MZZ40-P04] Orbit analysis of near-Earth asteroids

*Makoto Yoshikawa¹ (1.Japan Aerospace Exploration Agency)

Keywords:Near-Earth object, Planetary defense,, Orbit, Resonance

Due to the increased activity of planetary defense (spaceguard), which deals with the issue of small solar system bodies colliding with the Earth, the number of near-Earth objects (NEOs) discovered is rapidly increasing, reaching over 34,000 as of February 2024. The orbits of these discovered NEOs have been calculated, and it has been confirmed that they will not collide with the Earth in the near future, but there are still a large number of undiscovered celestial bodies. It is important for planetary defense to discover them early and investigate whether there is a possibility of a collision with the Earth or not. On the other hand, NEOs have the potential not only for scientific exploration but also for manned missions and utilization. Here, in order to examine the possibility of NEOs other than science, we decided to focus on asteroids that have almost the same orbital period as the Earth and investigate the nature of their orbital motion. According to the orbital data of asteroids as of May 2023, there were 179 asteroids with semi-major axes between 0.99au and 1.01au. In these objects, we investigated the characteristics of orbital evolution over ±5000 years around the present for 27 asteroids whose orbits have been accurately determined and have designation numbers, and found that there were 9 asteroids that were in a long-term resonance state with the Earth and 11 asteroids that were in a short-term resonance state with the Earth. In other words, one-third of asteroids with an orbital period of approximately one year are in a stable resonance state with the Earth on the timescale of human activity. These asteroids will remain within a certain range of distance from Earth, making it possible not only to explore them scientifically but also to use them for human activities. Furthermore, there is a possibility that some of the remaining 152 unnumbered asteroids may be in resonance with the Earth. This means that there may be a large number of asteroids that are in resonance with the Earth. We are currently analyzing the orbital evolution and approach to planets for more NEOs and will report about the results.