Lori Stiles

University of Arizona News Services

The idea that what humans witnessed and chronicled in 1178 A.D. was a major
meteor impact that created the 22-kilometer (14-mile) lunar crater called
Giordano Bruno is myth, a University of Arizona graduate student has
discovered.

And this should be welcome news for those worried by Deep Impact movie
scenarios.

The idea that 12th century people saw the impact that created a lunar crater
more than 10 times as wide as Meteor Crater in northern Arizona has been
popular since it was first proposed 25 years ago. But it doesn’t hold up
under scientific scrutiny, said Paul Withers of the UA Lunar and Planetary
Laboratory.

Such an impact would have resulted in a blinding, blizzard-like, week-long
meteor storm on Earth – yet there are no such accounts in any known
historical record, including the European, Chinese, Arabic, Japanese and
Korean astronomical archives, Withers said. He reports the analysis and
other tests of the hypothesis in this month’s issue of Meteoritics and
Planetary Science.

The dramatic passage in question appears in the medieval chronicles of
Gervase of Canterbury.

About an hour after sunset June 18, 1178 A.D., a band of five eyewitnesses
watched as the upper horn of the bright, new crescent moon “suddenly split
in two. From the midpoint of this division a flaming torch sprang up,
spewing out . . . fire, hot coals and sparks. . .The body of the moon ,
which was below writhed. . .throbbed like a wounded snake.” The phenomenon
recurred another dozen times or more, the witnesses reported.

A geologist suggested in 1976 that this account is consistent with the
location and age of Giordano Bruno, the youngest crater of its size or
larger on the moon.

A one-to-three kilometer wide (a half-mile to almost 5-mile wide) meteor
blasted Giordano Bruno into the northeast limb of the moon. Such an impact
on the Earth would be “civilization threatening,” causing regional
devastation to global climatic catastrophe – so it is important to know if
such an event happened on the moon less than a millennium ago, Withers
noted.

The impact would have launched 10 million tons of ejecta into the Earth’s
atmosphere in the following week, previous studies have shown, Withers said.
In the Meteoritics article, Withers reports his calculations on the
properties of the subsequent meteor storm.

“I calculate that this would cause a week-long meteor storm potentially
comparable to the peak of the 1966 Leonids storm.” Ten million tons of rock
showering the entire Earth as pieces of ejecta about a centimeter across
(inch-sized fragments) for a week is equivalent to 50,000 meteors an hour.

“And they would be very bright, very easy to see, at magnitude 1 or
magnitude 2. It would have been a spectacular sight to see! Everyone around
the world would have had the opportunity to see the best fireworks show in
history, ” Withers said.

Yet no vigilant 12th century sky watcher reported such a storm.

So what did the witnessess see that the Canterbury monk recorded?

“I think they happened to be at the right place at the right time to look up
in the sky and see a meteor that was directly in front of the moon, coming
straight towards them,” Withers said. This idea was strongly suggested by
others in a 1977 scientific paper.

“And it was a pretty spectacular meteor that burst into flames in the
Earth’s atmosphere- fizzling, bubbling, and spluttering. If you were in the
right one-to-two kilometer patch on Earth’s surface, you’d get the perfect
geometry,” he said. “That would explain why only five people are recorded to
have seen it.

“Imagine being in Canterbury on that June evening and seeing the moon
convulse and spray hot, molten rock into space, ” Withers added. “The
memories of it would live with you for the rest of your life.”

Contact:

Paul Withers, UA planetary sciences

520-621-1507, withers@lpl.arizona.edu