Unique volcanic complex discovered on Moon’s far side

NASA/GSFC/ASU/WUSTL, processing by B. Jolliff

Map of the abundance of the element thorium on the Moon made with data from the Lunar Prospector, a space mission launched in 1998, shows that most of this radioactive element is concentrated in a region on the Moon's near side (left).

But there is also a small hot spot called the Compton-Belkovich Thorium Anomaly (labeled C-B in the map) on the side of the Moon that faces away from Earth.

Analysis of new images of a curious “hot spot” on the far side of the Moon reveal it to be a small volcanic province created by the upwelling of silicic magma. The unusual location of the province and the surprising composition of the lava that formed it offer tantalizing clues to the Moon’s thermal history.

The hot spot is a concentration of a radioactive element thorium sitting between the very large and ancient impact craters Compton and Belkovich that was first detected by Lunar Prospector’s gamma-ray spectrometer in 1998.

The Compton-Belkovich Thorium Anomaly, as it is called, appears as a bull's-eye when the spectrometer data are projected onto a map, with the highest thorium concentration at its center.

Recent observations, made with the powerful Lunar Reconnaissance Orbiter (LRO) optical cameras, have allowed scientists to distinguish volcanic features in terrain at the center of the bull's-eye.

High-resolution three-dimensional models of the terrain and information from the LRO Diviner instrument have revealed geological features diagnostic not just of volcanism but also of much rarer silicic volcanism.

The volcanic province’s very existence will force scientists to modify ideas about the Moon’s volcanic history, says Bradley Jolliff, PhD, research professor in the Department of Earth and Planetary Sciences in Arts & Sciences at Washington University in St. Louis, who led the team that analyzed the LRO images.

“To find evidence of this unusual composition located where it is, and appearing to be relatively recent volcanic activity is a fundamentally new result and will make us think again about the Moon’s thermal and volcanic evolution,” he says.

The work is described in the July 24 advance online issue of Nature Geoscience.

Read more at Washington University St Louis