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Wednesday May 9, 2001

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UA grad student disproves theory on moon crater

By Jeremy Duda

Arizona Daily Wildcat

Medieval monks were standing at a confusing angle during meteor-burning entrance into atmosphere

What was previously thought to be evidence of the origin of a lunar crater may actually have been an optical illusion, according to a recent report by a UA graduate student.

The 14-mile crater on the surface of the moon, named Giordano Bruno, was theorized in 1976 to have been caused by the impact of a meteor during medieval times.

The basis of this theory is drawn from the chronicles of Gervase of Canterbury, a 12th century monk. In 1178, Gervase and four other observers in Canterbury, England witnessed an explosion of light in the sky near the upper horn of the crescent moon.

It was suggested that this is consistent with the location and age of the crater, which is the youngest on the moon's surface.

A recent report in Meteoritics and Planetary Science, though, suggests what these monks saw was not the impact of a meteor on the moon, but rather the disintegration of one in the earth's atmosphere.

"They were in the right place at the right time," said Paul Withers, a University of Arizona lunar and planetary sciences graduate student, who wrote the report.

In the report, Withers argues the crater could not have been created by a meteor, because such an impact would have caused an upheaval of rock that would have ended up in Earth's atmosphere.

"That would give you a dramatic meteor storm with 10 million tons of burning rock into the Earth's atmosphere," Withers said.

There are no accounts of any such meteor storm happening at that time.

What Withers believes medieval witnesses saw was a meteor burning up in Earth's atmosphere. Their location may have put the meteor in the direct line of sight between them and moon, he said.

Only people watching from within a mile or so of the monks' location would been able to see exactly what they saw, Withers said. Anyone watching from a different area "would have just seen a meteor in the sky."

This would explain the lack of documentation of this incident in astronomical archives written by other skywatching civilizations, which included China, Japan, Korea, Arabia and the rest of Europe.

"They weren't in the right place to see the alignment with the moon," Withers said.

Withers' report confirmed the suspicions of other astronomers who were also unsure of the 1976 theory.

"I thought it was a crazy hypothesis, but no one proved it until Paul," said Henry Melosh, a UA professor of lunar and planetary sciences, who Withers briefly consulted with on the physics of meteoric impacts.

"I don't think that anyone has previously worked out the calculations of what kind of meteor shower that would have caused," Withers said.

So far there has been little feedback over the report, Withers said, but most of what he has heard has been positive.

"It's only been out a week, so it's a little too soon for people to react," he said.