Violent winds and shockwaves would account for more than 60 per cent of lives lost if an asteroid were to hit the Earth, according to a new University of Southampton-led study.
Researchers explored seven effects associated with asteroid impacts – heat, pressure shock waves, flying debris, tsunamis, wind blasts, seismic shaking and cratering—and estimated their lethality for varying sizes. They then ranked the effects from most to least deadly, or how many lives were lost to each effect.
Overall, wind blasts and shock waves were likely to claim the most casualties. In experimental scenarios, these two effects accounted for more than 60 per cent of lives lost. Shock waves arise from a spike in atmospheric pressure and can rupture internal organs, while wind blasts carry enough power to hurl human bodies and flatten forests.
Senior research assistant Clemens Rumpf, lead author of the new study published in Geophysical Research Letters, a journal of the American Geophysical Union, said: “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.”
Mr Rumpf said his findings, which he plans to present at the 2017 International Academy of Astronautics Planetary Defense Conference in Tokyo, Japan, next month, could help hazard mitigation groups better prepare for asteroid threats because it details which impact effects are most dominant, which are less severe and where resources should be allocated.
Though studies like this are necessary to reduce harm, deadly asteroid impacts are still rare, said Mr Rumpf. Earth is struck by an asteroid 60 metres (more than 190ft) wide approximately once every 1,500 years, whereas an asteroid 400 metres (more than 1,300ft) across is likely to strike the planet every 100,000 years.
“The likelihood of an asteroid impact is really low, but the consequences can be unimaginable,” he said.
Rumpf and his colleagues used computer simulations to pepper the globe with 50,000 asteroids ranging from 15 to 400 meters (49 to 1,31ft) across—the diameter range of asteroids that most frequently strike the Earth. The researchers then estimated how many lives would be lost to each of the seven effects.
Land-based impacts were, on average, an order of magnitude more dangerous than asteroids that landed in oceans.
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. Even if a tsunami were to reach coastal communities, far fewer people would die than if the same asteroid struck land, Mr Rumpf said. Overall, tsunamis accounted for 20 per cent of lives lost, according to the study.
The heat generated by an asteroid accounted for nearly 30 per cent of lives lost. Affected populations could likely avoid harm by hiding in basements and other underground structures.
Seismic shaking was of least concern, as it accounted for only 0.17 per cent of casualties. Cratering and airborne debris were similarly less concerning, both responsible for less than one per cent of deaths.
Only asteroids at least 18 metres (nearly 60ft) wide were lethal. Many asteroids on the lower end of this spectrum disintegrate in Earth’s atmosphere before reaching the planet’s surface, but they strike more frequently than larger asteroids and generate enough heat and explosive energy to cause damage. For example, the meteor involved in the 2013 impact in Chelyabinsk, Russia, was 17 to 20 metres (roughly 55 to 65ft) across and caused more than 1,000 injuries, inflicting burns and temporary blindness on people nearby.
The study’s findings could help mitigate loss of human life, according to Mr Rumpf. Small towns facing the impact of an asteroid 30 metres across (about 98ft) may fare best by evacuating. However, an asteroid 200 metres wide (more than 650ft) heading for a densely populated city poses a greater risk and could warrant a more involved response, he said.
“If only ten 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.”
Source: University of Southampton