Planetary securityThe threat of asteroids and comets

In 1994, astronomers watched in awe as the comet Shoemaker-Levy 9 crashed into the planet Jupiter, creating massive fireballs exploding with the force of six million megatons of TNT—equivalent to 600 times the world’s nuclear arsenal.

What would have happened if it had hit Earth instead of Jupiter?

“It would be the biggest destruction that mankind has ever seen,” said Mel Stauffer, University of Saskatchewan geological sciences professor emeritus. “It wouldn’t matter where it hit, it would affect all mankind.”

The subject of Hollywood movies, the reality of asteroid and comet strikes is more science, than science fiction. Most researchers believe the likelihood of a massive object colliding with Earth in our lifetime is small, but the planet has been hit before and will certainly be hit again.

USask says that Stauffer has spent a lifetime collecting the evidence, searching for meteorites, shatter cones (rock violently fractured around the rim of impact craters) and tektites (pulverized rock liquified by the superheated temperature of an impact and blasted into the atmosphere before raining down to the surface).

Stauffer said on average the Earth gets hits by a one-metre-wide asteroid about once a year, although, most burn up in the atmosphere or crash into remote regions or our vast oceans. Two of the most alarming recent events occurred in the Siberian region of Russia, including the 2013 asteroid air burst near Chelyabinsk that was reported in the journal Nature to be a house-sized object 20 metres in diameter, releasing the energy equivalent of 440,000 tonnes of TNT.

“It went just past a couple of villages, including Chelyabinsk, and because it was breaking the sound barrier and exploding into pieces, the shock wave broke windows that blew up in people’s faces, so about 1,500 people were hospitalized from cuts,” said Stauffer. “It was the second largest event that we have been able to accurately measure.”