THE United States Air Force detected a massive explosion in December of last year when an asteroid blew up in our atmosphere.

The blast was ten times more powerful than the explosion from the atomic bomb that devastated Hiroshima, and had not been predicted.

It hit at around midday local time -- but because the impact happened over the Bering sea it was not widely noticed.

The rock, several metres across, burned through the upper atmosphere at 72,000 miles per hour before exploding 16 miles up.

It was the most powerful such explosion since a huge blast rocked the Russian region of Chelyabinsk in 2013.

Talking to BBC News, Lindley Johnson, planetary defence officer at Nasa said that a fireball this big is only expected about two or three times every 100 years.

The 173-kiloton explosion was 40 per cent as powerful as the Chelyabinsk blast, but came dangerously close to routes used by major airlines.

Many flights between the USA and Asia fly over the Bering Sea, and researchers have reached out to airlines to see if anyone actually saw the blast.

NASA tracks a number of so-called Near Earth Objects, but didn't have this one on their scopes.

In fact, Johnson revealed that NASA only found out about the impact when they were informed by the US Air Force, whose detection systems had picked up the massive explosion.

Nasa believes none of the thousands of NEOs that it keeps a close eye on are currently on a collision course with our planet.

"Nasa knows of no asteroid or comet currently on a collision course with Earth, so the probability of a major collision is quite small," it says.

"In fact, as best as we can tell, no large object is likely to strike the Earth any time in the next several hundred years."

In March, two 100-foot asteroids zipped past us under Nasa's watchful eye.

While an asteroid that big could cause major local damage around an impact site, it would need to be about twenty times that size to cause problems on a global scale.

Last month, Nasa released its best photos of yet of a potential doomsday asteroid known as Bennu.

As with the Chelyabinsk blast, no-one saw this one coming.