In November 2021, NASA launched a daring mission to smack a space rock lying 27 million kilometres from Earth. About 10 months later, the world saw, for the first time, a spacecraft deliberately slamming into an asteroid, in what was a bold step to build a planetary defense technology.
The mission was the Double Asteroid Redirection Test (DART) and the target was Dimorphos, a 525 feet or 160 meters wide rock that was orbiting another asteroid Didymos (measuring 2,559 feet or 780 meters).
When the impact occurred on September 26, 2022, it didn’t just prove a concept, it demonstrated that humanity can deflect a threatening asteroid and fundamentally enhance our planetary defense capabilities.
Killer rocks: The threat is real
The NASA’s Planetary Defense Coordination Office leads the search for potentially hazardous asteroids using telescopes like Catalina Sky Survey, Pan-STARRS and ATLAS, and space-based observatories such as NEOWISE. As of September 2025, the agency has discovered 39,123 near-Earth asteroids of all sizes, out of which 873 are larger than 1 km wide and 11,343 are larger than 140 meters.
Between October and September alone, as many as 12 near-Earth asteroids passed closer to the Earth than the Moon, and there were 176 asteroids which made their closest approach to our planet in the last 365 days. NASA says that their flybys bombarded Earth with 100 tons of dust and sand-sized particles, but since most of them burnup in the atmosphere, they never make it to the surface.
However, there have been instances when we were not so lucky. The Tunguska event of 1908 is one of the most talked about when one discusses the threat of asteroid impacts (other than the Chicxulub that killed the dinosaurs).
It was a quiet morning of June 30, 1908 when an asteroid exploded in the sky over Tunguska in Russia, at 7:15 am. The space rock was estimated to be between 30-40 meters wide and was travelling at approximately 1,00,000 km per hour. Even though it exploded between 6-10 km above the surface, the explosion released energy equivalent to 10-15 megatons of TNT. An expedition team, which went to explore the site nearly 20 years after the event, discovered that the asteroid had knocked over 80 million trees and completely destroyed more than 2,200 square km of forest area.
While there were no confirmed deaths from the explosion, several locals were knocked unconscious and herds of reindeers in the forest perished.
Russia witnessed a similar event in 2013, now remembered as the Chelyabinsk Impact, due to an explosion caused by an asteroid that impacted Earth’s atmosphere.
This also occurred several kilometres above the ground releasing energy equivalent to 4,40,000 tons of TNT and injuring 1,600 people within a radius of over 500 square km.
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Can asteroids be neutralised?
It may have seemed impossible before but DART proved it can be done. With this mission, NASA wanted to test and demonstrate a method of changing an asteroid’s motion in space using a ‘kinetic impactor.’
When the small car-sized DART spacecraft impacted Dimorphos at 21,960 km per hour, it managed to change the asteroid’s orbital period from 11 hours and 55 minutes to 11 hours and 23 minutes, shortening it by 32 minutes. The mission was flawlessly successful, proving that a mission like DART could be used to protect Earth from a collision with an asteroid.
Space agencies are now doubling down on this defense technique. In October 2024, the European Space Agency (ESA) launched the Hera mission that will rendezvous with Dimorphos in December 2026. The objective is to examine the twin-asteroid system post-collision and measure Dimorphos’s mass, study the crater left behind by DART and analyse the asteroid’s composition.
NASA is also building the NEO Surveyor space telescope to locate hazardous near-Earth asteroids that are hard to spot from the ground because they approach Earth from the direction of the Sun.
