Volcanic "fire fountains" erupting from the lunar surface, similar to what occurs in Iceland today, most likely were fueled by carbon monoxide gas, a new study shows.
Taking advantage of new analysis techniques, scientists re-analyzed the contents of green and orange glass beads discovered in soil samples brought back from the moon by the Apollo 15 and Apollo 17 missions, which took place in the early 1970s.
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"The lunar volcanic glasses are thought to be the product of fire-fountain eruptions, in which a jet of basaltic lava erupts through a vent, spattering droplets of lava that cool quickly to form glass," Bruno Scaillet, with the University of Orleans in France, wrote in an article in this week's Nature Geoscience.
The process is similar to shaking a can of soda and taking off the cap.
On Earth, the gas that triggers fire fountains is typically carbon dioxide or water.
The new analysis of the lunar samples showed that concentrations of carbon and water decreased toward the center of the beads, an indication of degassing. Follow-on studies with computer models show the fire fountains were most likely fed by carbon monoxide gas.
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"It was debated it could be carbon monoxide, but there was no evidence," Brown University lunar scientist Alberto Saal wrote in an email to Discovery News.
Another option is hydrogen gas, but there is not geologic evidence of a fluid rich in hydrogen, he added.
The researchers also point out that the concentrations of carbon in the lunar melts is basically the same as what is found in Earth basalts that erupted from the mid-ocean ridges.
Saal and colleagues previously showed that Earth and the moon have similar concentrations of water and other volatiles, as well as similar ratios of hydrogen isotopes.
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The studies have implications for ongoing efforts to determine how the moon formed. The leading theory is that Earth was hit by a Mars-sized object early in its history and that the debris eventually melded together to form the moon. How a common pool of volatiles could have survived the impact has yet to be resolved.
"The volatile evidence suggests that either some of Earth's volatiles survived that impact and were included in the accretion of the Moon or that volatiles were delivered to both the Earth and Moon at the same time from a common source -- perhaps a bombardment of primitive meteorites," Saal said in a statement.