Planetary Defense & NEO Operations

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.

A newly-found object's observations are reported to the Minor Planet Center, which links them into a single orbit. The more observations over a longer arc, the more precisely the future path is known.

Determining what an object is — its size, shape, spin, and composition — from light curves, radar, spectra, and, for a few, spacecraft visits. Hera is en route to survey the asteroid DART struck, to learn how a deflection actually worked.

Automatic systems at CNEOS and ESA continuously propagate every known orbit forward for a century or more, flagging any that could approach Earth. Apophis was tracked this way until observations ruled out an impact for the next century.

Judging how serious a possible impact is — its probability, the object's size and energy, and the time until the encounter — and expressing it on the Torino and Palermo scales so the risk can be understood and compared.

Explaining a risk to decision-makers and the public accurately and without alarm — including retracting a warning when better data clears an object, as happened with Apophis. Clear communication is itself part of planetary defence.

If an object were found on a collision course with enough warning, agencies and governments would decide on a response — and plan the reconnaissance and deflection mission it would require. NEO Surveyor is being built to give that warning decades ahead.

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.