Hazards of asteroid impact

VIOLENT winds and shock waves are the most dangerous effects that would be produced by earth-impacting asteroids, according to the first ever such study published in the recent issue of Geophysical Research Letters.

The study explored seven effects associated with asteroid impact—heat, pressure shock waves, flying debris, tsunamis, wind blasts, seismic shaking and cratering—and estimated their lethality for varying sizes.

The researchers 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, according to the study. In experimental scenarios, these two effects accounted for more than 60 per cent of the 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.

The findings could help hazard mitigation groups be better prepared for asteroid threats.

Though studies like this are important, deadly asteroid impacts are still rare, said Clemens Rumpf of the University of Southampton, U.K., and lead author of the study.

According to him, the earth is struck by an asteroid 60 metres wide approximately once in every 1,500 years, while an asteroid 400 m across is likely to strike the planet only once in every 100,000 years. While the likelihood of an asteroid impact may be really low, the consequences can be unimaginable, Rumpf said.

Rumpf and his associates used models to spray the globe with 50,000 artificial asteroids ranging from 15 m to 400 m 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 an average, of 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, Rumpf said. Overall, tsunamis accounted for 20 per cent of the lives lost, according to the study.

The heat generated by an asteroid accounted for nearly 30 per cent of the lives lost. Affected populations could likely avoid harm by hiding in basements and other underground structures, Rumpf said.

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 causing less than 1 per cent of the deaths.

Only asteroids that spanned at least 18 metres in diameter were lethal. Many asteroids on the lower end of this spectrum disintegrate in the 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 inflict damage. For example, the meteor involved in the 2013 impact in Chelyabinsk, Russia, was 17 m to 20 m across and caused more than 1,000 injuries, inflicting burns and temporary blindness on people nearby.