Psyche - an asteroid made almost entirely of nickel-iron metal.

Psyche, an asteroid made almost entirely of nickel-iron metal.

By Cristy Burne

LET’S get one thing straight: the chances of a deadly asteroid slamming into Earth are super-tiny.

If you lived for 1,500 years, you might see a 60-metre-wide asteroid strike just once. In 100,000 years you might see one 400-metre-wide asteroid hit. And the chances of any asteroid hitting your town are pretty much zero.

“The likelihood of an asteroid impact is really low,” says an asteroid researcher, Clemens Rumpf, who will speak at the planetary defence conference in Japan in May. “But the consequences can be unimaginable.”

That doesn’t mean it’s not fun to think about.

Mr Rumpf studied 1.2 million computer-generated asteroid impacts to work out what might happen if a real asteroid hit:

Heat

Danger ranking:

Lives lost: < 30 per cent

An asteroid ripping through Earth’s atmosphere bumps into loads of air molecules. This causes friction, which warms things up enough to form a massive fireball and searing heat.

Pressure shockwaves

Air pressure spikes as the asteroid enters Earth’s atmosphere. This creates shockwaves that can travel through the air with enough force to burst your blood vessels and organs.

Wind blasts

Wind blasts can throw you to the ground or flatten buildings and trees.

Combined danger ranking:

Combined lives lost: > 50 per cent

Cratering

Danger ranking: 

Lives lost: 0.2 per cent

Craters form only at the impact site, so you’d be mega-unlucky to be in this 0.2 per cent.

Flying debris

Danger ranking: 

Lives lost: <1 per cent

The explosive impact of an asteroid can send chunks of the Earth’s crust flying. You might want to watch the show, but keep your head down.

Seismic shaking

ranking:

Lives lost: 0.17 per cent  

The force of impact can be so massive it creates its own seismic shocks in the Earth’s crust, like earthquakes caused from above.

Tsunamis

Danger ranking:

Lives lost: 20 per cent

Asteroids that slam into the ocean can create tsunamis: powerful waves that cause lots of damage if they ever reach land. However, most tsunamis would run out of energy before hitting a coastline, says Mr Rumpf. Asteroids that strike water are much safer – and twice as likely – as those that strike land.

Near misses and more2013: a 17- to 20-metre-wide meteor exploded in mid-air over Chelyabinsk, Russia. About 1,000 people were injured, mostly by shockwaves that knocked them to the ground, or by broken glass flying through the air.

2013: a 45-metre-wide asteroid passed Earth, just 25,000 kilometres above us (closer than many satellites). Scientists discovered it a year before it arrived, and were confident it wouldn’t hit.

1908: a 30- to 40-metre-wide meteor flattened 2,000 square kilometres of forest – about 80 million trees – in Siberia, Russia. No people were injured.

66 million years ago: an asteroid at least 10 kilometres wide smashed into the ocean near Chicxulub, Mexico. It exploded with the force of 100 trillion tons of TNT, causing planet-wide destruction and the extinction of dinosaurs.

Scientists have used telescopes to find and track all the big near-Earth objects.

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