What is NASA doing about dangerous asteroids?
NASA funds sky surveys that find and track near-Earth objects, calculates their future orbits, coordinates planetary defence through a dedicated office, and has tested a way to deflect an asteroid with the DART mission.
NASA's work on dangerous asteroids, usually called planetary defence, has three main strands: finding them, working out where they are going, and testing ways to move one if needed.
Finding them comes first, because you cannot deflect what you have not seen. NASA funds ground-based telescope surveys that photograph the sky night after night, looking for faint points of light that move against the background stars. These surveys have discovered tens of thousands of near-Earth asteroids, including most of the largest ones, over a kilometre across. Because many asteroids are dark and some approach from the direction of the Sun, NASA is also building a space telescope called NEO Surveyor, designed to spot them by the heat they give off in infrared light. It is planned for launch in the late 2020s.
Once an object is found, astronomers measure its position repeatedly and calculate its orbit decades ahead. Automated systems check whether any known asteroid has even a small chance of hitting Earth, and the risk is updated as new observations arrive. Often an early, worrying probability falls to zero once the orbit is known more precisely, as happened with the asteroid Apophis. NASA's Planetary Defense Coordination Office, set up in 2016, oversees this work and would help warn government agencies if a real threat emerged.
The third strand is mitigation. In 2022 the DART spacecraft deliberately crashed into a small moonlet called Dimorphos and measurably changed its orbit, the first time humans have altered the motion of a natural celestial body. NASA also works with other agencies, including the European Space Agency, and takes part in international exercises in which scientists and emergency planners rehearse how they would respond to an imaginary incoming asteroid. None of this is cause for alarm: it is careful insurance.