Old impact. Giordano Bruno (arrow) probably didn't result from a cosmic collision in 1178.

Nothing But Moonshine

Did the meteoroid that crashed into the backside of the moon, leaving behind a 22-kilometer-wide crater named Giordano Bruno, cause the peculiar fountain of moonlight reported by a 12th century monk, as some researchers claim? No, says a new study--adding another nail to the coffin of this unlikely, but hard-to-test theory.

On 25 June 1178, five eyewitnesses visited a Canterbury monk named Gervase, claiming to have seen the crescent moon "spewing out fire, hot coals, and sparks." Almost 8 centuries later, a relatively young crater--dubbed Giordano Bruno, after the heretic who was burned at the stake in Rome for arguing that planets orbit other stars--was discovered on the far side of the moon by the Soviet spacecraft Lunik III. Since then, some scientists have argued that Gervase's records may describe the collision that formed Giordano Bruno.

Most astronomers were skeptical. Without a sample from the crater, it's nearly impossible to establish its age; in fact, it's estimated that Giordano Bruno could have formed anytime in the last 350 million years. The probability that it happened only 800 years ago is vanishingly small, but not zero. "It's a cosmic shooting gallery up there," says planetary scientist Clark Chapman of the Southwest Research Institute in Boulder, Colorado, "so the idea is not completely nuts."

If a meteor large enough to excavate Giordano Bruno did hit the moon in 1178, it would have showered an estimated 10 million tons of dislodged rock down on Earth, says planetary scientist Paul Withers of the Lunar and Planetary Institute in Tucson, Arizona. Withers has now calculated that most of the particles would be between 0.1 and 10 centimeters across. When these pebbles hit the atmosphere, they would have caused a brilliant week-long meteor storm visible throughout Europe and Asia. As there are no reports of such a shower, no meteoroid hit the moon on 18 June 1178, Withers concludes in this month's Meteoritics and Planetary Science.

"Withers's claim is perfectly reasonable," says planetary scientist Alan Harris of the Jet Propulsion Lab in Pasadena, California. "One would certainly have expected the sky to light up." Harris also adds that the shower would probably have repeated every year for a few decades until the cloud of moon rocks dispersed. No such annual meteor shower was ever reported.

Related sites

A PDF file of the paper (813 kB)
Paul Withers's home page
American Meteor Society