Scientists believe that lunar volcanoes stopped erupting about 1 billion to 1.5 billion years ago but a new study suggests that magma erupted on the moon less than 100 million years ago, which could mean that the timeline of lunar volcanic activity that scientists know of could be off by nearly a billion years.
In a report published in the journal Nature Geoscience on Oct. 12, Sarah Braden, from Arizona State University's School of Earth and Space Exploration, and colleagues managed to date a number of rocky formations on the lunar surface that were spotted by the Lunar Reconnaissance Orbiter (LRO) of the National Aeronautics and Space Administration (NASA).
The Lunar Reconnaissance Orbiter is a robotic spacecraft that has been orbiting the moon since 2009. The orbiter offers astronomers the best views of the lunar surface with its camera's ability to capture images with resolution that ranges from 50 to 200 centimeters per pixel.
By looking at the images captured by LRO, Braden and colleagues found 70 small volcanic features that are sprinkled across dark basaltic plains on the lunar surface called maria. The scientists called these features, which are characterized by mounds that lie on rough, blocky terrain and measure less than 5 kilometers across, irregular mare patches or IMPs.
It is believed that magma was regularly spewed out into the surface of the moon billions of years ago creating the maria. Volcanic eruptions then essentially stopped about a billion years ago but the relatively fresher appearance of the IMPs compared with their surroundings suggests that they impacted with space rocks no more than 100 million years ago, which indicate the possibility that the moon remained active for a much longer time than previously believed.
"Crater distributions from the three largest irregular mare patches imply ages younger than 100 million years, based on chronology models of the lunar surface," the researchers wrote. "The morphology of the features is also consistent with small basaltic eruptions that occurred significantly after the established cessation of lunar mare basaltic volcanism".
By looking at the crater sizes and numbers, the scientists were able to date the irregular mare patch and this revealed that volcanic activity on the moon did not abruptly stop a billion years ago. Instead, lunar volcanic activities gradually ended until as recent as less than 50 million years ago.
"The existence and young age of the irregular mare patches provides a new constraint for models of the lunar interior's thermal evolution," Braden said. "The lunar mantle had to remain hot enough for long enough to provide magma for the small-volume eruptions."
