'Moving target'

Threat of asteroid hit never gone, professors say after scare

This time, Earth was spared.

The mile-long asteroid 1977 XF11, which astronomers said last week could hit the Earth in 30 years, now seems to be sailing safely out of reach.

University professors warn that we may not always be so lucky. If more attention is not paid to the hundreds of potentially deadly objects that pass near Earth's orbit, they say one could catch us by surprise someday and cause global destruction.

"We are just a moving target," said Alexander Wolszczan, professor of astronomy. "There have been near misses and there will be near misses and eventually one is going to hit us."

If an asteroid the size of 1977 XF11 was to hit, the impact would be similar to 100 times the world's nuclear arsenal being detonated in the same place, said Bertil Olsson (graduate-geosciences).

- Alexander Wolszczan, professor of astronomy

The result could be temperatures dipping as low as minus 50 degrees Fahrenheit in Pennsylvania and, after 10 -to 15-foot tidal waves hit the coasts, low areas like Florida being submerged in water, said Darren Williams, assistant professor of physics at Penn State Erie. If it hit land, Olsson said, it could annihilate an area about the size of Belgium.

Such an impact would be smaller in scale, though fundamentally the same as the effect of the 5- to 6-mile asteroid that probably killed the dinosaurs 65 million years ago, Ackerman said.

The passing of an asteroid as close as 1977 XF11, which will at its closest be about twice as far as the moon, is not surprising, said James Kasting, professor of geosciences and meteorology. About every 100 years, an asteroid comes the distance of 100 Earth radii, Kasting said, though large impacts happen much less frequently.

"One expects to get a 10 kilometer impact every 100 million years and a one kilometer impact every million years," he said.

Wolszczan said smaller, but still major impacts happen every 100,000 years.

"The problem with statistics is you never know if it's going to be tomorrow or 100,000 years from now," he added.

Hopefully, Kasting said, the recent scare will direct more attention at avoiding potential collisions. Many of the potentially hazardous objects have not yet been detected, he said.

"Right now, we might not even (detect an asteroid) until we got hit," he said.

The first thing to do, Kasting said, is to map out all the potentially dangerous objects in the sky -- those that pass close to the Earth's orbit.

If a dangerous object is detected soon enough, he said small booster rockets could be attached to the object to send it off course.

- Bertil Olsson, graduate-geosciences

"If we knew that we would be impacted in a year then there would be some trouble," Williams said.

Even with 30 years to spare, Williams said we "might" be able to avert a collision with a 10 mile wide asteroid.

"We would send warhead after warhead at it," he said.

Olsson is even less optimistic.

"If it's the big one, we're pretty much toast anyway," he said.