Earth could be on a collision course with cosmic missiles


We have entered the new millennium without cataclysm, it's summer (sort of) and you might be enjoying long, restful days.

But as you contentedly watch smoke from another barbecue waft towards the stars, there comes a global health warning from a New Zealander just appointed to save the planet: the skies could still fall in.

Seventy-year-old physicist Harry Atkinson, the new head of a British taskforce assessing the risks of asteroids and comets pulverising Earth, admits it is a big "could."

Dr Atkinson, a graduate of Canterbury University and former head of the European Space Agency, heads a three-person team reporting to the British National Space Centre on the potential risks of a big cosmic collision.

He says the probability is "vanishing small" - the big strike that put paid to the dinosaurs 65 million years ago has been estimated as a one-in-eight-hundred-million-year event - but the potential destruction is so severe the risk cannot be ignored.

And Dr Atkinson pinpoints the Southern Hemisphere as a blind spot because of its lack of asteroid detection programmes.

"Nothing is being done there at the moment."

No one knows how many large pieces of space rock hurtle around on orbits that intersect with Earth's, but scientists theorise there are at least 1000 more than a kilometre wide - enough to cause a 20km-wide crater and serious climate problems.

Of those, about 250 have been detected by astronomers and their orbits found to cause no foreseeable risk.
(The dinosaur-unfriendly comet that smashed into the sea near Mexico's Yucatan Peninsula created a 300km-wide crater and its fallout caused widespread fires and plunged the world into a dark winter.)

That leaves 750 near-Earth objects with the potential to become too near Earth.

Two minor scares were detected recently: Asteroid XF11 was predicted to pass within a cosmically close 30,000km in 2028, and the comet Swift-Tuttle was thought to be on a collision course on its next visit in 112 years.

But further research on their orbits showed both would pass at a safe distance.

New Zealand astronomers share Dr Atkinson's concern for the lack of Southern Hemisphere detection programmes, but they are doing their bit to help.

Under the directorship of Dr Ian Griffin, who has found 20 or so asteroids in his United States-based career, the Auckland Observatory last year began an asteroid-hunting programme using sophisticated digital camera and computer technology.

They found two in the first week and six in total, although all are still awaiting official confirmation. Cloudy weather has hampered the programme.

An amateur astronomer at the observatory, Nigel Brady, says he believes one of the United States detection programmes is being extended to include an Australian base.

And Alan Gilmore, the head of Canterbury University's observatory at Mt St John, says it is preparing to resume work it pioneered in 1972 tracking the orbits of identified asteroids.

Many of the asteroids found could have been detected from both hemispheres, and it is impossible to know how many have been missed because of the lack of a southern programme.

But don't let any of this destroy your summer nights. Mr Brady sums up the risk of a collision: "It's like throwing a grain of sand on Eden Park and hitting one other grain of sand."

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