May 23, 2008


—written by Monte W. Holland and Carolyn C. Holland

My husband responded to a recent USA Today news article titled “That’s flashy: 100 explosions recorded on the Moon,” written by Tony Phillips,  [5/21/08]

“In 1959,” my husband began, “I was required to do a research project in my senior year at Union College (Schenectady, New York) where I majored in physics. My partner was Chuck Bruce, another physics major and an electronics person who had been into ham radio.

“We signed up to work with Professor Curtis Hemenway, in Albany, New York, at Dudley Observatory—which is owned by Union College. Professor Hemenway lived over in a residence attached to the observatory, which he maintained. The observatory also had a bedroom where researchers could sleep when not actively using the observatory.
“The professor’s idea was for us to look for meteors hitting the dark side of the moon. He believed these could be seen if we looked for flashes of infrared light.”

Not so long ago, anyone claiming to see flashes of light on the Moon would be viewed with deep suspicion by professional astronomers. Such reports were filed under “L” … for lunatic. (USA Today)

“We used an infrared photomultiplier tube and built a rotating slotted wheel that spun at a fixed speed in front of it. The theory was that we could have a tuned circuit that only picked up signals coming to the photomultiplier with the frequency associated with the spinning wheel, and eliminate random heat noise in the photomultiplier, enabling us to look for impacts on the dark portion of the moon. When the moon was in the correct phase, first or last quarters, and it was a clear night, we traveled to Albany for night.
“We blanked out the bright segment of the moon and looked at the dark part with the photomultiplier. It worked, but we never recorded any meteor hits.”

Over the past two and a half years, NASA astronomers have observed the Moon flashing at them not just once but one hundred times.

“They’re explosions caused by meteoroids hitting the Moon,” explains Bill Cooke, head of NASA’s Meteoroid Environment Office at the Marshall Space Flight Center (MSFC). “A typical blast is about as powerful as a few hundred pounds of TNT and can be photographed easily using a backyard telescope.”

The impactor (meteroid) was a tiny fragment of extinct comet 2003 EH1. Every year in early January, the Earth-Moon system passes through a stream of debris from that comet, producing the well-known Quadrantid meteor shower. Here on Earth, Quadrantids disintegrate as flashes of light in the atmosphere; on the airless Moon they hit the ground and explode. (USA Today)

“We never did determine the sensitivity of the instrument we made,” Monte said. “Looking back, I doubt we ever could have measured a hit, because our machine wasn’t sensitive enough. We were just kind of amateurs. 

“It surely was an adventure though.”

But perhaps a greater adventure would be walking around on the moon as uneventfully as one takes a walk in the park. But even then, there’s the worry: meteoroids hitting the moon!

“We started our monitoring program in late 2005 after NASA announced plans to return astronauts to the Moon,” says team leader Rob Suggs of the MSFC. If people were going to be walking around up there, “it seemed like a good idea to measure how often the Moon was getting hit.”
That first detection — “I’ll never forget it,” he says — came on Nov. 7, 2005, when a piece of Comet Encke about the size of a baseball hit Mare Imbrium. The resulting explosion produced a 7th magnitude flash, too dim for the naked eye but an easy target for the team’s 10-inch telescope.

Although there’s no oxygen on the moon, explosions still occur, since meteoroids hit the moon with tremendous kinetic energy due to their speed, 30.000 or more mph. The flash results from the impact heating the rocks and soil so hot that they glow like molten lava.

“Off-shower” impacts occur when bits of stray comet dust, part of a vast swarm of natural space junk littering the inner solar system, break off old asteroids and “pepper the Moon in small but ultimately significant numbers.” Suggs said that this means there is no time of the year when the Moon is impact-free.

The research team has upgraded their telescopes at the observatory, located at the Marshall Space Flight Center in Alabama, and now have multiple telescopes, which allow double- and triple-checking of faint flashes and improve the statistical underpinnings of the survey. They have also established a new observing site in Georgia.

Neither Monte nor I have an interest in moving south…but yet, in the retirement time of his life, perhaps Monte could return to his youthful experiments…

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