How you'd die in an asteroid impact

Asteroid earth
Uh-oh. This can't be good (Getty)

If a massive asteroid was to wipe out humanity, you might not care just how you die.

But in case you do: it'll probably be wind strong enough to flatten a forest hurling you through the burning-hot air.

Wind would account for about 60 percent of deaths in a Deep Impact-style disaster, new research out of the UK's University of Southampton suggests.

"This is the first study that looks at all seven impact effects generated by hazardous asteroids and estimates which are, in terms of human loss, most severe," says Clemens Rumpf, senior research assistant and lead author of the study.

His team looked at 50,000 different asteroids, using computer modelling to figure out what would happen if they hit in different places around the planet. They ranged from 15m across to 400m.

Worst-case scenario: a big one hits land. On average, an asteroid causes 10 times as much loss of life if it hits land, rather than the ocean.

"Large, ocean-impacting asteroids could generate enough power to trigger a tsunami, but the wave's energy would likely dissipate as it travelled and eventually break when it met a continental shelf," the researchers say.

"Even if a tsunami were to reach coastal communities, far fewer people would die than if the same asteroid struck land."

Heat would kill off about 30 percent of people, but could be avoided by hiding underground.

A shockwave strong enough to rupture internal organs would account for around 7 percent of deaths, but only if the rock was at least 40m across.

Seismic shaking caused by the impact would only account for a measly 0.17 percent of casualties. Airborne debris and the creation of the asteroid's crater would only cause 1 percent.

The Chelyabinsk meteorite (Reuters)
The Chelyabinsk meteorite (Reuters)

A meteorite 60m across or larger hits the Earth about every 1500 years. A 400m monster only hits about every 100,000 years. The rock that killed off the dinosaurs would have been about 10km across.

"The likelihood of an asteroid impact is really low," says Dr Rumpf. "But the consequences can be unimaginable."

To be lethal, a meteorite would need to be at least 18m across - about the length of four cars. Asteroids smaller than this generally burn up in the atmosphere, but have been known to cause damage - most notably in Russia's remote Chelyabinsk region in 2013.

Around 1000 people were injured when an asteroid about the size of a bus exploded, sending broken glass flying into the faces of people standing at their windows, looking at its bright flash.

"This report is a reasonable step forward in trying to understand and come to grips with the hazards posed by asteroids and comet impactors," says geophysicist Jay Melosh, professor at Purdue University in Lafayette, Indiana.

Dr Rumpf says the research will help authorities decide what to do in the event of an Earth-bound asteroid.

"If only 10 people are affected, then maybe it's better to evacuate the area. But if 1,000,000 people are affected, it may be worthwhile to mount a deflection mission and push the asteroid out of the way."

The study's findings have been published in Geophysical Research Letters, a journal of the American Geophysical Union.

Dr Rumpf will present his findings at the 2017 International Academy of Astronautics Planetary Defense Conference in Tokyo, Japan.