Closeapproaching

Closeapproaching is a term used in planetary science and astronomy to describe the short‑term proximity of a celestial object, such as an asteroid, comet, meteoroid, or spacecraft, to Earth or another planetary body. The phenomenon is quantified by the minimum orbital intersection distance (MOID), which is the smallest distance between the orbit of the object and that of the planet. When an object's MOID falls below a threshold—often 0.05 astronomical units for asteroids—the orbit is classified as potentially hazardous and the object is monitored for close approaches.

Close‑approaching objects are traditionally studied through optical or radar observations, allowing precise determination of their trajectories and physical characteristics. The data are fed into orbital propagation models that forecast future encounters, identifying potential impact risks and guiding mitigation strategies. In the case of spacecraft missions, engineers design flyby trajectories that exploit close‑approaching events to perform gravity assists or to rendezvous with small bodies, thereby reducing fuel requirements.

The habitability of Earth remains contingent on continuous surveillance of near‑Earth objects (NEOs). Events such as the 2013 Chelyabinsk meteor and the 2022 2020 PA3 close approach underscore the importance of early detection and risk assessment. Global initiatives like NASA’s Near‑Earth Object Program and the European Space Agency’s NEO Coordination Centre compile and publish data on close‑approaching bodies, enabling coordinated research and response efforts.

Understanding and cataloguing close‑approaching objects not only safeguards planetary assets but also offers scientific insight into the composition and dynamical histories of the solar system.