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Asteroid impact could deplete ozone layer
Posted: 26 October 2010

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An asteroid impacting into one of Earth's deep oceans would have an obvious effect – a tsunami – but a new study focuses on an equally alarming consequence: depletion of the Earth's protective ozone layer.

An asteroid striking one of Earth's deep oceans could have harming consequences on the ozone content of the atmosphere. Image: Don Davis/NASA.

Expert impact crater researcher Elisabetta Pierazzo of the Planetary Science Institute says that a ‘medium-sized’ asteroid – that is, one between 500 metres and one kilometre in diameter – crashing into Earth's ocean would send huge volumes of seawater into the air. “The results suggest that mid-latitude oceanic impact of one kilometre asteroids can produce significant global perturbation of upper atmospheric chemistry, including multi-year global ozone depletion comparable to large ozone hole sizes recorded in the mid 1990s.”

The computer models Pierazzo employed recorded the interaction of compounds such as chloride and bromide with the atmosphere, which promote the destruction of ozone. Ozone is an important component to our atmosphere, protecting us from the damaging effects of solar ultraviolet radiation. A natural depletion of ozone occurs every year over Antarctica as a result of unique atmospheric conditions, but a global depletion, as projected in Pierazzo's models, would result in a huge influx of ultraviolet radiation to the Earth's surface.

A natural thinning of the ozone layer occurs every year over Antarctica; this so-called ozone hole (blue-purple colours in this image) persists from September to December every year. Image: NASA.

“The removal of a significant amount of ozone in the upper atmosphere for an extended period of time can have important biological repercussions at the Earth’s surface as a consequence of increase in surface ultraviolet irradiance,” warns Pierazzo. “These include increased incidence of erythema (skin reddening), cortical cataracts, changes in plant growth and changes in molecular DNA.”

The ultraviolet index (UVI) is used to measure the intensity of UV radiation at the Earth's surface, and is often included in weather reports alongside temperatures in the summer months, with values typically below 10. The highest UVI recorded on Earth to date is 20, but the results of a 500 metre asteroid impacting into an ocean could reportedly lead to UVI values exceeding 20 for several months in subtropical regions. For a one kilometre diameter asteroid impact this value could reach 56 and persist for two years in latitudes as far reaching as 50 degrees north and south.

“A level of 56 has never been recorded before, so we are not sure what it is going to do,” she says “It would be produce major sunburn. We could stay inside to protect ourselves, but if you go outside during daylight hours you would burn. You would have to go outside at night, after sunset, to avoid major damage.”

Since the Earth has twice as much water by surface area than land, an Earth-bound asteroid has more chance of striking an ocean and causing these devastating effects than one destined for a collision with the continents. The new simulations are the first attempt at combining impact simulations with shock physics, atmospheric circulation and atmospheric chemistry, and an important step in fully understanding the effects of impacts on our home planet.