Asteroids - On a Collision Course

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Sometimes asteroids don’t just come to Earth in pieces; on occasion an entire asteroid has crashed into Earth. Sixty-five million years ago, a 10 km wide asteroid smacked into Earth in the Yucatan Peninsula in Mexico, leaving behind a 180 km wide crater called Chicxulub. The impact sent huge clouds of dust and ash into the sky, blocking out the Sun and sending temperatures across the world plummeting. The impact has been linked to the extinction of the dinosaurs, and although the impact may not have been solely responsible for their extinction, it almost certainly played a significant role. Several other extinctions in Earth’s history have also tentatively been linked to asteroid impacts.

Should we be worried about being wiped out by an asteroid impact? Not especially. It turns out that an asteroid 50m in diameter will collide with Earth every thousand years, and asteroids this size are capable of creating a crater 1 km wide. The famous Meteor Crater in Arizona is a good example of an impact of this size. A crater is always bigger than the asteroid that creates it, simply because of the amount of kinetic energy in the asteroid as it hurtles towards the ground.

A larger asteroid 1 km across is estimated to hit Earth on average every million years. An impact this size would release a whopping 40,000 megatons, blasting a crater 17 km from one side to the other in the ground, with a blast wave that can carry debris, flatten buildings and burn trees up to 300 km away. An impact of this size, whilst capable of doing lots of damage (especially if it landed in the ocean, causing a giant tsunami), wouldn’t threaten humanity with extinction. This threat lies with asteroids around 10 km in diameter, which impact on Earth on timescales of tens to hundreds of millions of years. So, based on those odds, we should be alright – for the time being at least.

Next Chapter: Meteorites