Lunar Flash Mystery Solved: Moon Just Passing Gas
Image of "transient lunar phenomenon" (TLP) taken in 1953. The TLP is the small, bright spot in the center of the image indicated by the arrow, and may have been caused by gassy material leaking out of the moon.
Credit: Leon Stuart/Columbia University Department of Astronomy

Changes in the brightness and color over small areas of the moon?s surface, known as Transient Lunar Phenomena, or TLP, have been observed telescopically for hundreds of years.

The optical flashes have been seen by skywatchers but rarely photographed.

?People over the years have attributed TLPs to all sorts of effects: turbulence in Earth's atmosphere, visual physiological effects, atmospheric smearing of light like a prism, and even psychological effects like hysteria or planted suggestion," said Columbia University researcher Arlin Crotts.

Using data from decades-old observations, Crotts and colleagues have now found a strong correlation between TLP sightings and regions where lunar orbiting spacecraft have detected gas leaking out from beneath the lunar surface.

?The areas selected consistently by TLP are the craters Aristarchus (in about 50 percent of sampled reports), Plato (about 15 percent) with Kepler, Copernicus, Tycho and Grimaldi all at the few percent level apiece,? Crotts said.

"This data ties in with observations made by the Apollo 15 and Lunar Prospector spacecraft which detected the gas radon-222 twice at Aristarchus and also once at Kepler and Grimaldi.

Moonquakes to blame?

Now Crotts and collaborators hope to achieve a larger sample of TLP sightings by using a robotic camera to keep watch on the moon in an effort to photograph any TLP events that may occur.

The camera, located at the Cerro Tololo Inter-American Observatory in northern Chile, will remove the gruesome task of continuously observing from the astronomer and provide observations free from the bias and inaccuracy that human eyes can introduce.

?It [the camera] will be more sensitive than the human eye/telescope combination, and more objective and persistent," Crotts said. "Hopefully it will give a better map of the TLP geographical distribution, as well as their timing and internal structure."

It is likely that the ghostly and fleeting TLP could be a manifestation of inert gases such as radon and argon being released from within the moon due to radioactive decay of uranium-238 and potassium K-40.

Moonquakes would seem a likely candidate for triggering the release of these gases but no correlation between TLP and moonquakes was found by Crotts.

?There is some small tendency for TLP to correlate with perigee (the moon?s closest point to the Earth in its orbit). Maybe there is a significant delay between moonquakes and resulting TLP. We don't know,? Crotts told

The findings have been submitted to the journal Icarus.

Boon to astronauts

Whatever mechanism initiates their release, Crotts suspects that the inert gases will be mixed with others of a more volcanic nature. "This is just speculation, but the prime volcanic suspects would be carbon monoxide (CO), carbon dioxide (CO2) and water (H2O),? Crotts said.

If lunar outgassing is a source of CO, CO2 or H2O, this could prove useful to future lunar colonies, supplying drinking water and fuel for example and saving billions of dollars in transportation costs. Hauling freight from Earth now costs about $10,000 per pound just to get from the launch pad to space.

Confirmation of the identities of the gases present could come courtesy of the Japanese lunar orbiter SELENE, due for launch later this year.

?SELENE will carry a better Radon-222 alpha particle detector than any ever before. We should be observing simultaneous to SELENE, so can correlate TLP and outgassing even more effectively,? Crotts said.

Future high resolution images from NASA?s Lunar Reconnaissance Orbiter and other planned lunar spacecraft will also be studied in the hope of detecting any permanent changes to the lunar surface accompanying TLP detected by the automated camera in Chile.

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