Wednesday, May 26, 1999

Nuke blast could
stop asteroid, comet
from crashing
into Earth

A Los Alamos physicist
says it's the only way to
prevent such a disaster

By Helen Altonn


The only method available to prevent an asteroid or comet from colliding with the Earth is to use nuclear explosives, says a Los Alamos National Laboratory physicist.

"That scares me as much as it scares you," Johndale Solem said, discussing the dangers of asteroids and comets in an interview yesterday. Solem is among more than 40 scientists from around the world attending a three-day Tsunami Symposium at the East-West Center sponsored by The Tsunami Society.

Discussions are focusing on dangers of mega-tsunamis created by an asteroid or comet impact.

David Crawford of Sandia National Laboratory in Albuquerque, New Mexico, noted that the most famous of 140 known impact craters on the Earth was created about 65 million years ago when a comet or asteroid landed in shallow water near the present town of Chicxulub, Mexico.

"With a kinetic energy equivalent to 100 trillion tons of TNT, the impact event lofted enough debris onto globe-straddling trajectories to flash-heat much of the surface of the Earth and then darken the skies for several years," he said. Many species were destroyed.

Solem said the chances of such an event occurring are small, but if an asteroid did hit Earth, "the implications would be exceedingly catastrophic."

A 100-meter (330-foot) object would have a high explosive equivalent of 1,000 megatons and an object the size of one kilometer (.62 of a mile) would have 1,000 times more energy, he said.

"So, it's just a lot of energy. But fortunately, it's rare."

It's now known that comets pose about the same hazards as asteroids and they're far more difficult to predict, Solem said.

An asteroid's probable collision with Earth may be recognized several years in advance, he said. However, comets blow off steam or ionized material and move around in a more unpredictable way, he said.

Although most emphasis at the conference is on asteroids or comets that might impact the ocean, causing massive, devastating tsunamis, Solem said smaller asteroids tend to dissipate most of their energy before impact.

Such an asteroid exploded this century over Tunguska Valley in Sibera, leveling about 1,240 miles of forest and killing at least two people, Solem said. "If that was over Los Angeles, for example, it would level most of the entire city."

The same sort of thing over the ocean has hardly any effect because the destruction is from an air blast, he said.

Solem described several techniques of using nuclear explosives to deflect or pulverize an asteroid or comet, depending on their size.

Explosives could be detonated on the object's surface to propel it away from the Earth. Or they could be detonated some distance from the surface, which would greatly lower the risk of fracturing the object, he said.

A lot is known now about nuclear explosives and putting things in space and intercepting objects, he said. "The greatest ignorance is in the composition of asteroids and comets, how they're made up."

However, NASA is planning missions to asteroids and comets to learn more about their composition and what holds them together, he said.

Use of explosives to prevent a comet or asteroid collision would be "a straightforward process," Solem believes.

"It would be more difficult getting the world together on a decision to do this," he added. "The outline of the mission would be scientific but it would be argued politically."

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