Sky-is-falling scenarios blast forth

Sunday, July 12, 1998

BY CHARLES BREWER
The Cincinnati Enquirer

A little more than 20 years ago, a movie was released that changed how we view the beach.

Jaws was the beginning of a summer phenomenon: the something-new-to-worry-about movie.

This summer, the hip thing to worry about is objects falling from the sky. Two competing movies, Deep Impact and Armageddon, depict the very real possibility of a cosmic collision.

After you've spent $7 to watch Bruce Willis save the world, perhaps you'd like to see what real meteorites and comets do to Earth. You need travel no farther than the nearest computer with an Internet connection.

About 50,000 years ago, a 300,000-ton chunk of iron about 150 feet across and traveling at 40,000 miles an hour slammed into the Arizona desert. The resulting explosion was equal to 20 million tons of dynamite.

The asteroid left a crater a mile wide and 570 feet deep. And it's still there: the Barringer Meteorite Crater at Meteor Crater, Ariz.

The story of the controversy surrounding the crater -- initially thought to be created by a volcanic eruption of steam -- and the eventual acceptance that it was caused by a celestial body is documented on an excellent Web site (http://www.barringercrater.com).

Impact sites identified

Surprisingly, the search for meteorite impact sites didn't start in earnest until the mid-20th century. Scientists have conclusively identified 150 impact sites and estimate that a serious meteorite strike occurs an average of every 1,000 years.

If true, we're probably safe for another millennium, since many think that a celestial object hit the Earth June 30, 1908.

Fortunately, it occurred in a mosquito-infested swamp near Tunguska, Siberia. The area is so remote that Russian scientists didn't visit the area until 1927.

What they found was astounding. An area of more than 2,000 square meters -- half the size of Rhode Island -- was leveled, with trees felled in a circular pattern. An area of 1,000 square kilometers was burned. Today, scientists think that the object was most likely a comet or asteroid weighing 100,000 tons. It exploded with the force of about 40 megatons of dynamite. Had it exploded over Europe, an estimated 500,000 people would have died. (The only known casualties of the collision was a large herd of reindeer.)

An interesting article on the Tunguska event is found at the Southworth Planetarium Web site at the University of Southern Maine (http://www.usm.maine.edu/planet/tung.html). At the beginning of this century, scientists generally thought that the Earth's atmosphere provided a shield that incinerated any cosmic objects before they could strike the ground. As we approach the next century, scientists are using supercomputers to predict what could happen if a large object hit the Earth.

Collisions described

At Scientific American's site (http://www.sciam.com/explorations/), two articles describe the effects of collisions with a comet and an asteroid.

One, aptly titled "Bang and Splat," focuses on a comet-vs.-Earth computer simulation created at Sandia National Laboratories. The scientists assumed that the comet has a better chance of hitting water than land, so they sent their one-kilometer comet crashing into the ocean. The 300-gigaton blast would send sea water into space and create a cloud of steam and dirt that would shroud the Earth in darkness.

At Los Alamos National Laboratory, scientists sent a virtual asteroid into the sea. The resulting tidal wave reached the foothills of the Appalachian Mountains.

Both computer simulations are available at the Scientific American Web site, although Hollywood's versions are more exciting. Perhaps the summer of 1998 will be remembered as the summer that changed the way we view the heavens.

Send e-mail to Charles Brewer at CBrewer@enquirer.com.

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