Some were more powerful - in one case, dozens of times stronger - than the 15-kiloton atom bomb that destroyed Hiroshima in 1945.
The impacts were recorded by the Nuclear Test Ban Treaty Organisation which has a global network of sensors to listen for nuc-lear weapon detonations.
Most occurred too high in the atmosphere to cause any serious damage on the ground. But the evidence is a reminder of how vulnerable the Earth is to the threat from space, say scientists.
None of the asteroids were detected or tracked in advance by any space or Earth-based observatory.
Former astronaut Ed Lu, who spoke about the new data at the Museum of Flight in Seattle, US, said: "While most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10,000 of the more than a million dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially-operated observatories."
Dr Lu is chief executive of the B612 Foundation, which is dedicated to finding ways of protecting the Earth from dangerous asteroids.
In 2013, a 600 kiloton meteor explosion above the Russian town of Chelyabinsk caused extensive damage to property.