Look out! It’s almost Asteroid Day

Tuesday is the first annual Asteroid Day, an attempt by a coalition of scientists and celebrities to raise public awareness of the risks posed by space rocks striking the earth.

People are being encouraged to sign an international petition to governments encouraging them to spend more in defence of the planet.

The goal is to step up efforts to identify impactors such as comets and asteroids before they reach us and to devise ways to steer these objects away from our orbit.

It all sounds very science fiction but the earth has always been at risk of being struck by such objects and the danger continues today.

Recent strike

The Chelyabinsk

meteor

exploded in the upper atmosphere over

Russia

in February 2013, showering the ground below with large fragments. It injured 1,500 people and damaged more than 7,000 buildings but luckily there were no recorded deaths.

The largest impactor in modern history also occurred over Russia, the Tunguska Event of June 30th, 1908. The asteroid flattened about 2,000sq km, an area the size of that within London's M25 ring road, said Prof Mark Bailey, director of Armagh Observatory.

It landed in Siberia so it was forests that were destroyed, but had it struck a city like London the deaths and losses would have been staggering.

Chelyabinsk was 20m across while Tunguska measured more than 60m. Imagine, then, what the damage would be like with an impacting object 10km across. This is the estimated diameter of the impactor that wiped out the dinosaurs 66 million years ago.

It struck the earth at the northern tip of the Yucatán Peninsula in Mexico, leaving an impact crater 180km across and 20km deep. It sent billions of tonnes of material into the atmosphere, blotting out the sun and wiping out life on land and sea.

Global impact

Impactors have therefore had a powerful effect in shaping the biological history of the planet, forcing evolution to come up with organisms capable of living in a new environment post-collision.

Nor has the threat eased with time. Worldwide efforts to track these objects have identified more than 10,000 that cross our orbit. Of these, 867 have diameters of at least 1km, a size capable of having a global impact.

Armagh Observatory doesn’t look for them. It is trying to understand where they come from and why they have strange orbits. “The interesting question we are looking at is: are we currently in a high or low occurrence rate,” said Prof Bailey. “It looks like a lower rate, but this could be followed by a period of heightened activity.”