太陽系小天体の地球衝突問題を扱う活動をプラネタリーディフェンスと呼ぶ。この活動は1990年代から本格的に始まったが、現在、目覚ましい進展がある。地球接近天体（NEO）は現在3万個以上発見されており、10個以上のNEOへ探査機が送られた。2022年には、NASAのDARTミッションによる小惑星の軌道を変更する試みが成功した。2024年には、ESAのHeraミッションが打ち上げられ、DARTの衝突の結果を詳しく調査する。OSIRIS-APEX、「はやぶさ2#」などのNEOミッションも行われている。2029年にはアポフィスが静止衛星軌道よりも近くまで接近するが、OSIRIS-APEXは地球最接近の数日後に到着する予定であるし、接近前に到着するミッションもいくつか検討されている。国際的には、国連の下に設置されたグループにおける議論や国際会議、アウトリーチ活動など多岐にわたる活動が活発に行われている。本セッションでは、NEOやプラネタリーディフェンスに関する観測や探査、理論的・技術的研究、社会科学的検討など様々な観点から現状を整理し、今後どのような国際的な取り組みや協力を行うべきなのか議論する。

The activities that focus on the avoidance of collisions of small solar system bodies such as asteroids and comets with the Earth belong to the topic called planetary defense. These activities began in earnest in the 1990s. Now, nearly 30 years later, there has been remarkable progress. More than 33,000 Near Earth Objects (NEOs) have been discovered so far, and spacecraft have been sent to more than 10 NEOs. Furthermore, in 2022, the DART mission by NASA made the first attempt to change the orbit of an asteroid using a kinetic impactor successfully. The ESA Hera mission will launch in October 2024 to investigate in detail the results of the DART impact as well as the characteristics of its target. In parallel, other NEO missions such as OSIRIS-APEX (an extended mission of OSIRIS-REx) of NASA, and Hayabusa2# (an extended mission of Hayabusa2) of JAXA are on their way to their respective target. In 2029, the asteroid Apophis will come closer than Earth's geostationary satellite orbit to our planet, and is the target of OSIRIS-APEX that will visit the asteroid a few days after its closest approach to the Earth. Several concepts are also under study to visit Apophis before and during its passage, offering a great possible international synergy with OSIRIS-APEX. Internationally, a wide range of activities such as discussions in groups established under the United Nations, international conferences, and outreach activities are actively carried out. This lively situation motivates presentations on ongoing relevant activities in various areas covering ground and space based investigations, theoretical/technical research, as well as social science research on NEO and planetary defense. We will also discuss what kind of research or action, including international cooperation, should be undertaken from now on for the protection of our planet against an impact.