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Loading contentFinding, tracking, and — if ever needed — deflecting the near-Earth asteroids. A routine scientific monitoring effort, described factually and without alarm.
Dedicated survey telescopes scan the sky nightly for moving points of light and compute the orbits of everything they find. The most productive include Pan-STARRS in Hawaiʻi, the Catalina Sky Survey in Arizona, and ATLAS, with the Vera C. Rubin Observatory and NASA's planned NEO Surveyor infrared space telescope expected to greatly expand the catalogue. The overall effort traces back to the 1990s Spaceguard goal of cataloguing the large near-Earth asteroids.
When a new object's orbit is uncertain, astronomers estimate its impact probability and communicate it on two scales. The Torino Scale is a 0–10 public-facing scale combining impact probability and energy; almost every object sits at 0, and values are routinely revised down to 0 as more observations refine the orbit. The Palermo Scale is a finer logarithmic scale used by specialists to compare a hazard against the background impact risk. These are communication tools, not predictions — objects are added and then removed as tracking improves, which is the system working as intended.
NASA's Planetary Defense Coordination Office (PDCO) leads U.S. efforts, working with ESA's Space Safety programme and, internationally, with the UN-endorsed International Asteroid Warning Network (IAWN) and Space Mission Planning Advisory Group (SMPAG). Orbits and observations are collected by the IAU Minor Planet Center, and impact-monitoring systems at NASA/JPL's CNEOS and ESA continuously reassess the known catalogue.
The right technique depends on the object's size and how many years of warning are available — which is why early discovery is the foundation of planetary defense.
The bodies at the centre of the DART and Hera planetary-defense missions.
A near-Earth binary asteroid whose small moon, Dimorphos, was struck by NASA's DART in 2022 — humanity's first test of asteroid deflection.
The small moon of the near-Earth asteroid Didymos and the impact target of NASA's DART mission — the first object whose orbit humans deliberately changed. ESA's Hera will survey the aftermath.
Modelled near-Earth asteroids meeting the objective PHA size-and-distance criterion — a monitoring category, not a prediction of impact.
One of the most elongated known asteroids, a near-Earth Apollo object well characterised by radar.
An elongated near-Earth asteroid in a chaotic, tumbling rotation, flown past by China's Chang'e 2 in 2012; it crosses both Earth's and Mars's orbits.
A near-Earth asteroid famous for its very close but non-impacting approach to Earth on 13 April 2029; impacts for the foreseeable future have been ruled out by radar and tracking.
A small, carbon-rich near-Earth asteroid sampled by OSIRIS-REx, whose material was returned to Earth in 2023.
A carbonaceous near-Earth asteroid visited by Japan's Hayabusa2, which returned surface and subsurface samples to Earth in 2020.
Well-studied past impacts — the reason the surveys exist.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
European missions, observatories, and space science imagery.
Orbital data, ephemerides, and small-body parameters for planets, asteroids, and comets.