NearEarth

NearEarth, also written as near-Earth, is a term used in space science to describe objects and phenomena whose orbits bring them into proximity with Earth. In practice, it most often refers to near-Earth objects (NEOs), primarily asteroids and comets that pass through the inner solar system near our planet.

NEOs are typically defined by orbital criteria such as a perihelion distance q ≤ 1.3 astronomical units, which brings their orbits into Earth’s neighborhood. They are categorized into classes including Atens, Apollos and Amors, and, in some classifications, interior-Earth or Atiras that stay mostly inside Earth’s orbit.

Discovery and tracking rely on dedicated surveys and observatories. Key programs include the Catalina Sky Survey, LINEAR, Spacewatch, Pan-STARRS and NEOWISE. Data are coordinated by the Minor Planet Center, while NASA’s Center for Near-Earth Object Studies (CNEOS) computes orbits and impact probabilities and runs the Sentry risk monitoring system.

The study of NEOs supports planetary defense by assessing impact risk and guiding potential deflection concepts, as well as providing scientific insight into solar system formation and evolution and resource prospects for future exploration.

Beyond individual objects, near-Earth space underpins a growing field of exploration. Missions such as OSIRIS-REx and Hayabusa2 have studied near-Earth asteroids, while future surveys and missions aim to increase discovery, characterization and potential utilization of these small bodies.