by Doug Ashbury
Northern News Services

NNSL (Nov 26/97) - It's not a question of if, but when, says scientist Buck Sharpton.

At some point in the future a meteor or comet will cross paths with the Earth's orbit, he said. The chance of a meteor or comet hitting earth is "absolutely 100 per cent."

But in the short term, there is no need for concern, he added.

Sharpton, with NASA's Lunar and Planetary Institute in Houston, spoke Sunday at the Prince of Wales Heritage Centre. He also spoke Tuesday night at the GeoScience Forum at the Explorer Hotel.

Sunday was a general look at meteors and how they've touched the Earth's history. His topic last night was a meteor crater on Devon Island known as the Haughton astrobleme.

About every 200 years, a meteor big enough to cause a crater with a diameter of a dozen kilometres slammed into the earth. A 20-kilometre crater is made about every 100 million years while a crater 150 kilometres across is made once every 100 million to 300 million years.

Sharpton pointed to one meteor known as Ida. It has a diameter of 60 kilometres and if it hit the Earth it would "sterilize" the planet.

But we are safe from Ida, he said.

As example of just how devastating these cosmic impacts are, Sharpton also showed a slide of the fireball created by a comet which hit Jupiter.

"The Earth would easily fit inside the fireball," he said.

The biggest hit of all occurred at the end of Mesozoic Era, when a object, likely a comet, collided with what is now the Yucatan peninsula in Central America. This impact is widely believed to be the cause of the extinction of dinosaurs -- in all about 70 per cent of all life on earth was obliterated -- everything bigger than a dog.

The Yucatan crater is between 200 and 300 kilometres across.

If an object from space is on course with Earth, there needs to be a plan to "nudge" the harm off course, he said.

Despite the danger, there is very little effort to monitor the night sky.

About a dozen new comets are spotted each year, many by astronomers acting alone.

Key to preventing damage to civilization as we know it is a better understanding of the paths taken by celestial bodies as they zoom through space at thousands of kilometres per second.

Their routes "need to be mapped," Sharpton said.