Astronomers have reported the cataloguing of the 40,000th near-Earth asteroid, marking a significant milestone in the tracking of potentially hazardous space rocks that orbit close to our planet. This achievement underscores the ongoing threat posed by these asteroids.
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Near-Earth asteroids, which vary in size from a few meters to several kilometers, have orbits that can bring them within approximately 45 million kilometers (28 million miles) of Earth's orbit. This proximity makes them of considerable interest to scientists and planetary defense experts.
An asteroid is defined as a rocky remnant from the formation of the Solar System over 4 billion years ago. While most asteroids reside in the main asteroid belt between Mars and Jupiter, near-Earth asteroids can come significantly closer to our planet.
The first near-Earth asteroid discovered was Eros in 1898. Over the following decades, the use of dedicated asteroid survey telescopes has dramatically increased the number of identified nearby celestial bodies. As of November 2025, the count surpassed 40,000, with around 10,000 new discoveries made in the last three years alone.
Luca Conversi, manager of the European Space Agency (ESA) Near-Earth Object Coordination Centre, noted a rapid rise in asteroid discoveries, with the number growing from 1,000 at the beginning of the century to 15,000 in 2016 and reaching 30,000 in 2022. Future telescopes, such as the Vera C. Rubin Observatory in Chile and ESA’s Flyeye telescopes, are expected to enhance these discovery rates further.
When a new near-Earth asteroid is identified, scientists analyze its trajectory using extensive observational data. Advanced software can project the asteroid's orbit for years or decades, assessing the likelihood of an Earth impact. Currently, nearly 2,000 near-Earth asteroids are categorized as having a 'non-zero chance' of impacting Earth within the next century, but most of these pose little danger.
ESA highlights that the largest near-Earth asteroids, those over 1 kilometer in diameter, are easier to track and are believed to be mostly accounted for. The greater concern now lies with mid-sized asteroids, ranging from 100 to 300 meters across, which remain challenging to detect. Predictions indicate that only about 30% of these mid-sized threats have been identified.
Since the discovery of Eros, researchers have made significant strides in cataloguing near-Earth asteroids, providing a clearer understanding of the potential threats from space and strategies for planetary safety.