London: If a medium-sized asteroid were to land in the oceans a tsunami wouldn't be the only worry, say scientists- the Earth's ozone layer could be at risk too.
A new computer simulation suggests that the water vapour and sea salt thrown up by the impact could damage the protective ozone layer, leading to record levels of ultraviolet radiation that could threaten human civilisation.
Elisabetta Pierazzo of the Planetary Science Institute in Tucson, Arizona, and colleagues used a global climate model to study how water vapour and sea salt thrown up from an impact will affect ozone levels for years after the event.
They focused on medium-sized asteroids, either 500 metres or 1 kilometre wide. To date, 818 asteroids that are at least 1 km wide have been discovered on orbits that could take them close to Earth.
These objects are on orbits that give them a very small probability of hitting Earth in the near future. However, estimates of the asteroid population suggest dozens more have yet to be found, with unknown orbits that could intersect with the Earth.
To get a sense of how much water might be jettisoned into the atmosphere if these asteroids hit the ocean, the team modelled what would happen if they reached Earth''s atmosphere at a clip of 18 kilometres per second, an average speed expected for a near-Earth object, and hit the ocean in the northern hemisphere at a 45-degree angle.
As expected, the simulations showed that the larger, 1-km asteroid created the bigger splash, throwing 42 trillion kilograms of water and vapour - enough to fill 16 million Olympic-sized swimming pools - across an area more than 1000 kilometres wide and up to hundreds of kilometres above the Earth''s surface.
Once in the atmosphere, the water, together with compounds containing chlorine and bromine from vaporised sea salts, destroyed ozone above the Earth''s atmosphere at a much faster rate than it is naturally created.
Some simulated impacts created depletions that were still felt across the whole Earth a year later.
"It will produce an ozone hole that will engulf the entire Earth," New Scientist quoted Pierazzo as saying.
The study has been published in the journal Earth and Planetary Science Letters.
First Published: Tuesday, October 26, 2010, 13:29