Astronomers have now cataloged 40,000 near-Earth asteroids (NEAs), a major milestone in planetary defense. These rocky remnants from the Solar System’s formation orbit close enough to Earth’s path—within about 45 million kilometers—to warrant careful tracking.
The pace of discovery has accelerated dramatically. From the first NEA found in 1898, it took over a century to identify 1,000. Thanks to dedicated survey telescopes, the count reached 15,000 by 2016 and 30,000 by 2022. An astonishing 10,000 new NEAs have been found in just the last three years, pushing the total past 40,000.
New observatories promise even faster discovery rates. The recently inaugurated Vera C. Rubin Observatory in Chile and ESA’s upcoming Flyeye telescopes, with their ultra-wide fields of view, are expected to find tens of thousands more.
While the largest asteroids—those capable of causing global effects—are believed to be almost entirely found, the current focus is on detecting mid-sized objects (100-300 meters wide). These pose a serious regional threat, and only an estimated 30% of them have been discovered so far.
Of the 40,000 known NEAs, about 2,000 have a non-zero, though typically very low, chance of impacting Earth within the next century. Crucially, none are currently a concern for the foreseeable future.
The effort goes beyond mere discovery. ESA’s Planetary Defence Office, through its Near-Earth Object Coordination Centre, continuously refines impact risk assessments. Furthermore, Europe is actively developing the capability to deflect a threatening asteroid. The Hera mission is en route to study the aftermath of NASA’s DART impact test, while the planned Ramses mission will rendezvous with the asteroid Apophis before its close Earth flyby in 2029. The future NEOMIR satellite will also close a critical blind spot by detecting asteroids approaching from the sunward side.
What began as a single discovery has grown into a robust global defense network, making our planet safer with every new asteroid found.
