[A-OS11] Continental Oceanic Mutual Interaction - Planetary Scale Material Circulation

[AOS11-05] Orbital analysis of Mars-approaching asteroids

★Invited Papers

*Makoto Yoshikawa¹ (1.Japan Aerospace Exploration Agency)

Keywords:Orbit, Celestial collision, Asteroid, Mars, Planetary defense

Recently, various activities have been conducted regarding collisions of small solar system bodies such as asteroids and comets with the Earth. This activity is called planetary defense or spaceguard. In particular, if a celestial body larger than a certain size collides with the earth, it will cause a large-scale natural disaster, so there has been much discussion about what can be done to prevent such damage. On the other hand, since there are no humans living on Mars, the possibility of a celestial body colliding with Mars has not been much of a concern from a planetary defense perspective. Here, we will examine the approach of asteroids to Mars from the perspective of orbit analysis. Regarding the approach of a small celestial body, first, as a simple check, we have checked whether the orbit of the asteroid intersects with the orbit of the Earth or Mars when the orbits of the celestial bodies are projected onto the ecliptic plane. As a result, as of May 2023, there were approximately 20,000 asteroids intersecting Earth's orbit, while there were approximately 50,000 asteroids intersecting Mars' orbit. For Mars, the number is more than double, but in the case of Earth, since observations are made from Earth, even smaller asteroids that approach Earth are observed, and there is a large bias here. If we include even smaller asteroids for Mars, more asteroids must be approaching Mars. This means that Mars is at a much higher risk of collision with asteroids. However, the condition that the orbits projected on the ecliptic plane intersect is a fairly loose condition for celestial bodies to approach each other, so it is necessary to investigate the approach of celestial bodies more definitively. One way to do this is to check the minimum orbit intersection distance (MOID) between the planet's orbit and the asteroid's orbit. Furthermore, it is more straightforward to calculate the orbital motions of celestial bodies and find out how close they actually approach each other. We are currently analyzing the orbits of asteroids approaching Mars using these methods, and will report on the results in comparison with those for Earth. In particular, some types of asteroids contain water, and we will also consider the approach of such asteroids to planets.