Asteroids hitting Earth cause atomic-scale blasts

Asteroids hurtling towards the planet and threatening to wipe out entire cities are normally the preserve of Hollywood blockbusters like 'Armageddon'.

But scientists have found that there could be some truth to the hysteria, as asteroids hitting the earth caused 26 nuclear-scale explosions between 2000 and 2013.

Some were more powerful - in one case dozens of times stronger than the 15-kiloton atom bomb blast that destroyed Hiroshima in 1945, according to impact analysis recorded by the Nuclear Test Ban Treaty Organisation.

The asteroids, which were not detected or tracked in advance by any space or Earth observatory, were large enough to wipe out entire cities, said former astronaut Ed Lu.

Most occurred too high in the atmosphere to cause any serious damage on the ground, but the evidence is said to be a sobering reminder of how vulnerable Earth is.

Presenting the findings from the global network of sensors, which listens for nuclear detonations at the Museum of Flight in Seattle, US, Lu said: "While most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10000 of the 1million-plus dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially operated observatories."

The most dramatic asteroid impact in recent times was in Tunguska, Siberia, in 1908, when an asteroid exploded with the force of up to 15000 tons of dynamite, flattening an area of remote forest covering 1200km².

A 600-kiloton meteor explosion above the Russian town of Chelyabinsk last year caused extensive damage to property.

Asteroid impacts greater than 20 kilotons occurred in South Sulawesi, Indonesia, in 2009, the Southern Ocean in 2004, and the Mediterranean Sea in 2002.