In a breakthrough discovery, scientists have found the volatile gas that drove eruptions on the moon.
Fire fountains require the presence of volatiles mixed in with the erupting lava. Volatile compounds turn into gas as the lavas rise from the depths. That expansion of that gas causes lava to blast into the air once it reaches the surface, a bit like taking the lid of a shaken bottle of soda.
The research suggests that lava associated with lunar fire fountains contained significant amounts of carbon. As it rose from the lunar depths, that carbon combined with oxygen to make substantial amounts carbon monoxide (CO) gas. That CO gas was responsible for the fire fountains that sprayed volcanic glass over parts of the lunar surface.
In the research, Author Alberto Saal of the Brown University and his colleagues carefully analysed glass beads brought back to Earth from the Apollo 15 and 17 missions.
They looked at samples that contained melt inclusions, tiny dots of molten magma that became trapped within crystals of olivine.
The researchers devised a theoretical model of how gases would escape from lunar magma at various depths and pressures, calibrated from the results of high-pressure lab experiments. The model had long been used for Earth.
The model showed that carbon, as it combines with oxygen to form CO gas, would have degassed before other volatiles.
Saal said that most of the carbon would have degassed deep under the surface, and added that other volatiles like hydrogen degassed later, when the magma was much closer to the surface and after the lava began breaking up into small globules, that suggested that carbon was driving the process in its early stages.
The study is published in the Journal Nature Geoscience.
