October 25, 1992

Article at Reuters

Astronomer warns of end of world in 2126

Comet Swift-Tuttle, the source of the annual Perseid meteor shower (NASA)

By Wilson da Silva

SYDNEY – A huge comet is on course to collide with Earth on August 14, 2126, and could kill off most forms of life with an explosion more powerful than a million nuclear bombs, an expert on asteroids told a space conference on Sunday.

The five-km-(3.1-mile)-wide ball of ice and rock is travelling so fast that, if it does collide full-on, it could plunge the world into the dark ages, astronomer Duncan Steel of the Anglo Australian Observatory told delegates in Sydney.

“It would create an impact force of 20 million megatonnes, or about 1.6 million times the force of the bomb dropped on Hiroshima,” said Steel, an authority on asteroids and leader of the world’s second biggest asteroid discovery team.

“Hopefully we personally are safe, our children are safe and even our grandchildren are safe, but it appears that our great grandchildren are not safe,” he told the Second Australian Space Development Conference.

The International Astronomical Union (IAU), the world astronomy authority, noted the comet’s discovery on October 15 and for the first time since keeping records of such finds, could not rule out a collision with Earth, Steel said.

Named Comet Swift-Tuttle, it was first sighted in 1862 and rediscovered in September this year.

Astronomers have since been watching the comet, travelling at 60 km (37 miles) per second, and early calculation of its path around the sun led to the IAU announcement.

“It... seems prudent to track the comet for as long as possible,” IAU astronomer Brian Marsden said in an official circular, which Steel tabled at the conference.

Because asteroids and comets speed up as they fall toward the sun and slow as they return to the outer solar system, astronomers need extremely precise measurements before they can accurately calculate their position in space at any one time.

“We need to track it for five or six years to be sure. If it’s going to hit it will be on August 14, 2126 because that’s when its path intersects the Earth’s,” Steel said.

There are hundreds of thousands of asteroids – spinning pieces of space rock – circling the sun which stay safely between the orbits of Mars and Jupiter.

But 3,000 wayward asteroids bigger than one km (0.62 miles) are believed to intersect the Earth’s orbit, only 150 of which have been catalogued and their orbits analysed by the 15 scientists worldwide who search for them, Steel told the meeting.

“A one to two kilometre (half-mile to 1.2 mile) object hitting the Earth would wipe at least 75 per cent of mankind, probably 95 per cent,” Steel said. “An impact in the ocean is no less dangerous than an impact on land.”

An impact this large has been estimated to occur once every million years, and astronomers calculate a 0.01 to 0.1 per cent chance of such a cataclysm will occur within a century.

A collision 65 million years ago is believed by some scientists to have wiped out the dinosaurs.

“Something needs to be done now, we need to identify all Earth-crossing asteroids and comets,” Steel told Reuters.

Smaller objects, of 50 to 100 metres (164 to 328 feet), also pose a threat. These are thought to strike every 100 years and would create an explosion of between 20 and 100 megatonnes, bigger than any nuclear weapon ever detonated, he said.

A 60-metre (200-foot) asteroid in 1908 streaked through the air and exploded over remote Siberia, levelling an area the size of New York, astronomers say. Some 300,000 asteroids bigger than 100 metres are calculated to cross our path.

Anything larger than one kilometre “is the sort of thing that’s on the threshold of wiping out mankind,” Steel said.