Planetary defense

Planetary defense is the detection, tracking, and mitigation of asteroids and comets that could collide with Earth. It combines astronomical surveys, impact-risk assessment, and strategies to prevent or reduce damage.

Near-Earth object: An asteroid or comet whose orbit brings it within 1.3 astronomical units of the Sun. These objects are the population planetary-defense surveys seek to find.
DART mission: NASA's 2022 mission that deliberately struck the asteroid moonlet Dimorphos to test kinetic deflection. It demonstrated that a spacecraft impact can measurably alter an asteroid's orbit.
Asteroid: A small rocky or metallic body that orbits the Sun and is smaller than a planet. Most monitored impact threats are asteroids.
Impact event: The collision of a natural celestial body with a planet or moon. Impact consequences depend on an object's size, speed, composition, and location.
Asteroid deflection: A deliberate change to an asteroid's trajectory intended to prevent a collision with Earth. Deflection changes the threat itself rather than managing the aftermath.
Asteroid survey: A systematic search that detects and tracks asteroids, often using repeated telescope observations. Repeated sky scans reveal objects before a close approach becomes an emergency.
Dimorphos: The small moon of the asteroid Didymos, whose orbit was changed by NASA's DART spacecraft. Its measured orbital change provided the central result of the DART deflection test.
Comet: An icy Solar System body that releases gas and dust as solar heating warms its surface. Long-period comets can arrive with less warning than many asteroids.
Impact winter: A prolonged global cooling that can follow an impact when dust and aerosols block sunlight. Large impacts can threaten ecosystems far beyond the immediate blast zone.
Asteroid disruption: An attempt to break an asteroid into smaller pieces, potentially changing its impact pattern. Unlike deflection, disruption risks leaving multiple fragments on dangerous trajectories.

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