Apollo mission astronauts discovered beads of volcanic glass on the surface of the moon, indicating fountains of fire once erupted in the region. Now, scientists believe they have solved the mystery behind the source of the eruptions in a finding that could help determine how the moon was formed.
A team of researchers identified a volatile gas that is believed to have triggered violent fiery explosions on the moon, Brown University reported. Fire fountains are known to occur in Hawaii, and require the presence of volatile compounds mixed in with lava. The volatiles turn into gas as the lava rises, and the expansion of this gas causes the lava to explode into the air.
"The question for many years was what gas produced these sorts of eruptions on the Moon," said Alberto Saal, associate professor of earth, environmental, and planetary sciences at Brown. "The gas is gone, so it hasn't been easy to figure out."
This new research suggests lunar lava contains carbon, which could have triggered fire fountain-like eruptions. To make their findings, a team of researchers looked at glass beads brought back to Earth from the Apollo 15 and 17 missions using a new state-of-the-art ion probe technique.
"This breakthrough depended on the ability of Carnegie's NanoSIMS ion probe to measure incredibly low levels of carbon, on objects that are the diameter of a human hair," Erik Hauri from Carnegie Institution for Science, who developed the technique. "It is really a remarkable achievement both scientifically and technically."
The findings suggested the lunar volcanic material contained between 44 and 64 parts per million carbon. The researchers created a theoretical model to demonstrate how gases would escape from lunar magma under a variety of temperature and pressure conditions. The model showed carbon gas would have degassed before other volatiles.
"Most of the carbon would have degassed deep under the surface," Saal said. "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 suggests carbon was driving the process in its early stages."
The findings also suggest volatile reservoirs within the moon have a common origin with those on Earth. The amount of carbon detected in the lunar samples is very similar to what is seen in basalts erupted at Earth's mid-ocean ridges. If volatile reservoirs on the moon and Earth do indeed have a common origin, it could confirm suspicions that the moon formed when Earth was hit by a Mars-sized object that sent debris flying into space.
"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 concluded.
The findings were published in a recent edition of the journal Nature Geoscience.
