Understanding Planetary Defense
How humanity would find and, if necessary, deflect a hazardous asteroid — the surveys, the risk scales, and the missions like DART that have shown an asteroid can be moved. Built on real programs; speculative methods are marked as such.
Related entities
- NEO pipeline stage
NEO Discovery
Dedicated survey telescopes scan the sky night after night for moving points of light — the near-Earth asteroids and comets. Catalina, Pan-STARRS, and ATLAS lead the search from the ground, and the Rubin Observatory will transform it.
- Impact-risk scale
The Torino Scale
A 0–10 scale, like a hazard traffic light, for communicating the risk of a near-Earth object to the public — combining impact probability and energy into a single colour-coded number. Apophis briefly reached level 4, the highest ever, before further observations returned it to zero.
- Deflection method
Kinetic Impactor
Crashing a spacecraft into an asteroid at high speed to nudge its orbit — and getting an extra push from the plume of debris thrown off. NASA's DART did exactly this to the moonlet Dimorphos in 2022, measurably shortening its orbit; ESA's Hera is on its way to study the result up close, arriving in late 2026.
- NEO pipeline stage
Deflection
The last stage — actually changing an asteroid's orbit so it misses the Earth. DART showed a kinetic impactor works; a gravity tractor, ion beam, or, as a last resort, a nuclear device are other options, chosen by how much warning time is available.