Buried lunar craters filled by lava long ago

by Lucas Joel
Thursday, June 16, 2016

The nearside of the moon with highlands (lighter regions) and maria (darker regions). Credit: NASA.

Craters dot much of the nearside of the moon. And buried beneath this pockmarked landscape, according to the latest findings from NASA’s two Gravity Recovery and Interior Laboratory (GRAIL) spacecraft, are the remnants of even more craters, many of which were covered long ago by lava.

The moon’s surface has two distinct landscape types: highlands and maria (singular: mare), typically visible in lunar maps as lighter- and darker-colored regions, respectively. The maria are composed of basalt that flooded parts of the surface during volcanic eruptions billions of years ago.

In a new study published in Geophysical Research Letters, a team led by Alexander Evans, a postdoctoral researcher at Southwest Research Institute in Boulder, Colo., reports finding more than 100 “quasi-circular mass anomalies” between 26 and 300 kilometers in diameter, many buried beneath the surface of the maria. The researchers interpreted the anomalies as craters left behind by impacts that occurred prior to or during the volcanic eruptions, and which were subsequently filled in and obscured by basalt between about 3.8 billion and 2.5 billion years ago.

From the dimensions of the buried craters, the researchers inferred that mare deposits on the moon’s nearside have an average thickness of at least 1.5 kilometers. However, they noted, there must be “lenses of mare material as thick as [about] 7 kilometers” for the largest mass anomalies observed to have been fully buried.

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