Washington University, St. Louis | Diana Lutz | 2011 July 24
Hotspot Found on Moon's Far SideAnalysis 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)
Discovery News | Stuart Gary, ABC Science Online | 2011 July 25
Non-mare silicic volcanism on the lunar farside at Compton–Belkovich - BL Jolliff et alScientists have found evidence of volcanoes on the far side of the moon.
The new discovery, reported in the journal Nature Geoscience is a rare example of volcanism on the lunar surface not associated with asteroid, meteor or comet impact events.
Until now the best known examples of volcanism were on the moon's near side in a region known as the Procellarum KREEP terrane.
A team of scientists, led by Bradley Jolliff from Washington University in St Louis, used images and other data gathered by NASA's Lunar Reconnaissance Orbiter (LRO) to assess the composition of an unusual region on the far side of the moon called the Compton-Belkovich thorium anomaly.
They focused on an area containing numerous domes, some more than six kilometers high.
The domes featured steeply sloping sides which Jolliff and colleagues interpret as, "volcanic in origin and formed from viscous lava."
"We also observe circular depressions, which we suggest result from caldera collapse or volcanic vents," the researchers write.
The LRO data indicates the rocks are rich in thorium, silica and alkali-feldspar minerals, making them different from the black basalts that make up the lunar mare on the near side.
Sarah Maddison, an associate professor of Astrophysics at Swinburne University in Melbourne said such a localized region of volcanism on the lunar far side is unusual.
"Most of the volcanism we see on the moon is impact related and on the near side, although we don't know why," said Maddison.
"But if it's caused by radioactive decay, then why is it limited to the one hot spot and why did it happen so much later than everywhere else on the moon?"
Geology lecturer Ian Graham from the University of New South Wales said the discovery is highly significant.
"It's much higher in silicon and potassium than the basaltic volcanism seen elsewhere on the moon" said Graham.
"It's also the first evidence of such young volcanic activity on the lunar surface, meaning the moon was still geologically active just 800 million years ago, rather than 1.2 billion years ago as previously thought."
Graham said, "It's been 42 years this month since we first walked on the moon and we're still finding out new things."
"It shows there's certainly good scientific justification to send people back there."
- Nature Geoscience (online 24 July 2011) DOI: 10.1038/ngeo1212
Rare Volcanoes Discovered On Far Side of the Moon
Space.com | Nola Taylor Redd | 2011 July 25
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