[M-ZZ45] Planetary defense - what should we do?

[MZZ45-P07] Orbit analysis of near-Earth asteroids

*Makoto Yoshikawa¹ (1.Japan Aerospace Exploration Agency)

Keywords:Near-Earth object, Orbit, planetary defense

In recent years, the activities of planetary defense have become very active internationally, and progress has been made in various fields such as observation and exploration of celestial bodies approaching the Earth, investigation of Earth collision avoidance, disaster prevention and social science issues. In particular, the discovery of near-Earth Objects (NEO = Near-Earth Object: defined as having a perihelion distance of less than 1.3 au) is progressing rapidly, and currently (February 2023) over 31,000 NEOs have been discovered. Among them, about 20,000 asteroids intersect the Earth's orbit, if we ignore the spatial orientation of the orbit. In addition, the number of celestial bodies that are actually approaching the Earth is increasing, and since 2020, it has been confirmed that more than 100 asteroids are approaching inside the lunar orbit every year. In the last six years, there have been about 40 asteroids that have approached less than one tenth of the Earth-Moon distance. In addition, there have been seven asteroids that have hit the Earth that were discovered before they hit the Earth. Here, we summarize the characteristics of the orbits of such bodies that approach the earth or the earth's orbit. Among these near-Earth asteroids, there are asteroids that are moving at almost the same orbital period as the Earth and such asteroids are attracting attention for their potential of exploration and utilization. From the orbital data of asteroids released at present, we can extract more than 170 objects whose semimajor axis is between 0.99au and 1.01au. They have an orbital period of almost one year, but their orbits are distributed from the inside of the orbit of Mercury to the outside of the orbit of Mars. We also report the characteristics of the orbital motion of such asteroids.