Are We Sitting Ducks in a Cosmic Shooting Gallery?
By John Howard
The film Deep Impact - about meteors hitting Earth and causing devastating ocean waves - may not be mere Hollywood hokum as Wednesday's meteor explosion over New Zealand revealed.
While the film's spectacular special effects leaves audiences reeling, a growing number of scientists believe that they may be too close for comfort.
Many astronomers accept that meteor impacts pose a serious threat, with evidence for scores of impacts having been found around the world.
On widely accepted theory for the extinction of the dinosaurs, for example, has it that 65 million years ago something the size of a mountain landed on the Yucatan peninsular in Mexico. Millions of tons of dust, water vapour and smoke from the resulting firestorm were thrown high into the atmosphere, where they blocked the sun's rays; the planet cooled and the dinosaur's literally chilled out.
But it's even closer to home than that.
Scientists have found disturbing evidence that Australia suffered a likely meteor attack only 200 years ago, in a catastrophe still recounted in Aboriginal legends.
Sediment and boulders along the coast of New South Wales are consistent with a tsunami hundreds of feet high, striking at a speed of more than 400 km/h - and a meteor is seen as the likely culprit.
They have also found evidence for tsunamis hitting other sites around Australia. The geomorphic signatures of such events have been found on Lord Howe Island in the mid-Tasman Sea, along the north Queensland coast and along the northwestern coast of Western Australia.
At the latter location, there is good evidence that a recent wave swept more than 50 kilometers inland, topping 100 metre hills more than 2 kilometers from the coast.
The events are consistent with a legend still recounted by Aborigines, which speaks of a "white wave" falling from the sky and devastating their culture. Until now, historians had linked the legend with the arrival of white settlers in the 1780's. However, it is now thought that a vast tsunami would give the impression of a white wave falling out of the sky.
Meteor impact experts at Spaceguard in South Australia say there is lots of evidence that earthquakes or mudslides would not be big enough to cause giant tsunami's but even small comet fragments can detonate in the atmosphere at a height needed to create huge tsunami's.
Meteor storms, known as Taurids, have been detected by instruments left on the Apollo missions in 1975. A direct hit from even a small fragment could cause billions of dollars in damage and kill thousands.
New Zealand was fantastically lucky on Wednesday but the close call underlined the importance of taking the cosmic threat seriously.