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Consumer Reports


Solving a 50-year lunar mystery

http://www.jewishworldreview.com | (UPI) -- On a clear evening on June 25, in the year 1178, five monks in Canterbury, England, gazed at the slim crescent of the new moon and saw an extraordinary sight.

"Suddenly, the upper horn (the crescent moon was commonly described as having two horns, as a cow or bull) split in two," the monks reported. "From the midpoint of the division, a flaming torch sprang up, spewing out fire, hot coals, and sparks."

The monks were unaware they probably were witnessing the impact of an asteroid-sized body on the lunar surface, which some astronomers have estimated happens only about once every 100,000 years.

Yet such events might occur considerably more often, because in the early morning hours of Nov. 15, 1953, Leon Stuart observed -- and photographed -- something very similar to the event reported by the monks only 775 years earlier.

Stuart, then an amateur astronomer in Tulsa, Okla., saw a massive, white-hot fireball rising from the center of the moon's face.

As dramatic as the event seemed, and as unusual as his photograph was, taken with a camera attached to his 8-inch telescope, Stuart would have to endure skepticism about his find for the remaining 15 years of his life -- and 35 years beyond that.

Despite numerous lunar mapping missions and six manned lunar landings during the years of the Apollo program, "Stuart's Event," as it became known in astronomy circles, remained unproven. As a result, skeptics attributed his photo was the result of such ordinary phenomena as lens flare or a meteorite entering Earth's atmosphere.

Now, two Californians, Bonnie J. Buratti, a scientist at NASA's Jet Propulsion Laboratory in Pasadena and Lane Johnson of Pomona College in Claremont, have taken a fresh look at the 50-year-old lunar mystery. They have come up with some highly persuasive evidence that Stuart's photo was both real and historic -- the first image of a planetary impact.

"Stuart's remarkable photograph of the collision gave us an excellent starting point in our search," Buratti said. "We were able to estimate the energy produced by the collision. But we calculated that any crater resulting from the collision would have been too small to be seen by even the best Earth-based telescopes, so we looked elsewhere for proof."

Reporting in the latest issue of the space journal Icarus, Buratti and Lane said they concentrated their investigation on the 35-kilometer (21.75-mile) wide region where the impact likely occurred. This allowed them to rule out most of the 10,000 or so craters pocking the surface of the near side of the moon -- the side always turned toward Earth.

At first, their efforts were just as unsuccessful as those of earlier investigators. When the duo re-examined photographs taken from the Lunar Orbiter spacecraft in 1967, none of the craters appeared a likely candidate. But then they consulted the more detailed imagery taken from the Clementine spacecraft in 1994.

"Using Stuart's photograph of the lunar flash, we estimated the object that hit the moon was approximately 20 meters (66 feet) across, and the resulting crater would be in the range of 1-to-2 kilometers (0.62 to 1.24 miles) across. We were looking for fresh craters with a non-eroded appearance," Buratti said.

The telltale sign of a "fresh" lunar crater is a bluish tinge to its surface, she explained. The blue indicates lunar subsoil has been exposed and hasn't yet been affected by a process called "space weathering," which reddens the soil. Another sign of a fresh crater is it reflects more sunlight than its surroundings.

Buratti and Lane's search of Clementine images revealed a 1.5-kilometer (0.93-mile) wide crater with the signal blue layer of material surrounding the impact site. The crater also was located in the middle of area covered by Stuart's 1953 photograph.

It seems the perfect candidate, they said. Its size is consistent with the energy produced by the observed flash, it has the right color and reflectivity and it is the right shape.

Buratti and Lane estimate the energy released at impact was about 0.5 megatons of TNT, or about 35 times more powerful than the Hiroshima atomic bomb.

"To me this is the celestial equivalent of observing a once-in-a-century hurricane," Buratti said. "We're taught the moon is geologically dead, but this proves that it is not. Here we can actually see weather on the moon."

Although Stuart died in 1968, his son Jerry said his father would have been pleased by Buratti and Lane's findings.

"Astronomy is all about investigation and discovery," he said. "It was my father's passion."

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