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Moon: Mound on Moon's South Pole Rose Up in Massive Volcanic Impact?

Oct 15, 2015 02:11 PM EDT
Top: South Pole-Aitken basin. Lower: Mafic Mound and nearby formations.
New research notes that a 47-mile wide mound in a crater on the moon's south pole was likely formed in a very dramatic volcanic event.
(Photo : NASA/Goddard/Arizona State University for top; NASA/Goddard/MIT/Brown University for bottom.)

A very large mound on the moon's south pole appears to have resulted from volcanic processes. Is this the new (or old) Mount Fuji or Kilimanjaro?

If so, it's an awfully wide one. A research team led by Brown University recently published the results of a study suggesting volcanic origins for the mound, which is made of different minerals than surrounding rocks and formations, according to a release.

The formation is called the Mafic Mound and measures about 2,600 feet tall and 47 miles across--yes, 47 miles. It is in the center of an impact crater called the South Pole-Aitken Basin.

The research team believe the mound resulted from a certain kind of volcanic activity created by the impact that caused the basin. Their paper on this has been accepted for publication by Geophysical Research Letters.

"If the scenarios that we lay out for its formation are correct, it could represent a totally new volcanic process that's never been seen before," Daniel Moriarty, a Ph.D. student in Brown University's Department of Earth, Environmental and Planetary Sciences and lead author of the study said in a release

This large mound, named for a term that denotes rocks that are rich in minerals such as olivine and pyroxene), was discovered by Carle Pieters in the 1990s. He is a planetary geologist at Brown and is advisor to Moriarty.

The mound's mineralogical make-up differs from the surrounding rocks. It contains high-calcium pyroxene; other nearby rocks are low in calcium.

"This unusual structure at the very center of the basin begs the question: What is this thing, and might it be related to the basin formation process?" Moriarty said in the release.

Moriarty and Pieters examined data from several exploration missions to the moon. Some of the data came from the Moon Mineralogy Mapper, which arrived there aboard India's spacecraft the Chandrayaan-1.

The combined data indicate that Mafic Mound was likely formed by one of two volcanic processes instigated by the impact that formed the large surrounding crater. Some researchers think that such a strong impact would have made a vat of melted rock 30 miles deep or less. After that cauldron formed, it would have shrunk. Then molten material in the middle of the vat might have squeezed out, like "toothpaste from a tube," according to the release. It's possible that that squeezed-out material formed the mound.

Models of how the melt sheet could have crystalized indicate that such erupting material would be full of high-calcium pyroxene, which is a match with the mound's mineralogy.

Alternatively, the researchers think the massive impact could have shot rocks out of the basin, created a low-gravity area, and allowed the basin's center to force itself upward. This would have partially melted the mantle and could have erupted, forming the mound.

Both hypotheses fit well with the datasets available, Moriarty said in the release. Any returns to the basin could fetch back lunar mantle bits. These could help firmly date when the impact took place, and could add information for dating other features on the mound and its surrounding area-as well as a unique volcanic process that occurred on the moon.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

-Follow Catherine on Twitter @TreesWhales

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