Our moon once had eruptions of "fire fountains" on its surface, similar to eruptions often seen today in Hawaii, and scientists say they've identified the driving force behind the lava fountains.
Fire fountains happen when there are volatile compounds mixed in with the erupting lava that expand into gas as the lava rises from the depths.
Like a shaken bottle of soda that's suddenly opened, the lava bursts into the air under the influence of the gas — in the case of the moon, researchers have discovered, that gas was carbon monoxide.
"The question for many years was what gas produced these sorts of eruptions on the Moon," says Alberto Saal of Brown University, one of the authors of a study appearing in Nature Geoscience. "The gas is gone, so it hasn't been easy to figure out."
On Earth, fire fountains are normally triggered by a combination of water and carbon dioxide.
The lava creating the lunar fire fountains likely contained large amounts of carbon that combined with oxygen as the lava rose from deep within the moon to form carbon monoxide, the researchers suggest.
That gas would have driven the fire fountains that left volcanic glass sprayed over regions of the lunar surface, they say.
Samples of the volcanic glass, in the form of tiny glass beads, were brought back to Earth during the Apollo 15 and 17 missions and were analyzed by Saal and his colleagues as part of their research.
Using sophisticated instruments, they were able to confirm the presence of carbon in the beads.
"The carbon is the [element] that is producing the large spectacle," says Saal. "With a little bit of water, with a little bit of sulfur — but the main driver is carbon."
The study strongly hints at the moon's makeup being very similar to that of the early Earth, he says, with less difference between the volatile elements here on Earth and those on the moon than scientists had previously believed.
That is in line with the current theories on moon's having been formed when the Earth was struck by a Mars-sized object early in hits history, with the ejected debris eventually coming back together to form our lunar companion.
"All these volatile elements ... are in concentrations that are very similar to the lava that formed the ocean floor of the Earth," he says.
Saal was also the leader of a team of researchers that, in 2008, was the first to discover traces of water on the moon while studying similar volcanic glass samples.
