NASA

A long time ago, before we knew her, the moon used to spew jets of fire into space. This is something scientists have known about for decades, since astronauts found beads of volcanic glass on the lunar surface during the Apollo missions.

The question, however, of what caused these eruptions was unanswered until this week, when researchers from the Carnegie Institution for Science and Brown University published research in Nature Geoscience offering an explanation: Carbon.

Co-author Alberto Saal said in a statement that “the question for many years was what gas produced these sorts of eruptions on the Moon." Until recently, scientists thought that the type of volatile gases that would lead to explosions of fire were absent from the moon. But in 2008, Saal and others were able to break down the components of the glass beads. In a discussion of the recent findings, the Carnegie Institution explains:

For this research, Saal and his colleagues carefully analyzed glass beads brought back to Earth from the Apollo 15 and 17 missions. In particular, they looked at samples that contained melt inclusions, tiny dots of molten magma that became trapped within crystals of olivine. The crystals trap gases present in the magma before they can escape.

The authors write in their abstract that "carbon degassed before water in lunar magmas, and that the amount of carbon in the lunar lavas was sufficient to trigger fire-fountain eruptions at the lunar surface." This means that carbon was the first to start seeping out from the moon's surface, and the driver behind the fire.

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The carbon discovery also suggests that the moon and the Earth have similar origins, helping scientists understand the origin of the rocky object.

Danielle Wiener-Bronner is a news reporter.