Chinese Rover Discovers New Type Of Moon Rock

The lunar rover Yutu has discovered a new kind of moon rock, providing hints of the Moon’s volcanic activity.

AsianScientist (Dec. 23, 2015) – New data gleaned from moon rock gathered by Chang’e-3, an unmanned lunar mission, has revealed a more diverse Moon than thought. The data, published in Nature Communications, is the result of two partnerships, one between Chinese institutions involved with the Chang’e-3 mission, and another educational partnership between Shandong University in Weihai, China, and Washington University in St. Louis.

In 2013, Chang’e-3 touched down on the northern part of the Moon’s Imbrium basin, one of the most prominent of the lava-filled impact basins visible from Earth.

The lander touched down on a smooth flood basalt plain next to a relatively fresh impact crater that had conveniently excavated bedrock from below the regolith (the ground-up surface layer of fragmented rock).

Since the Apollo program ended, American lunar exploration has been conducted mainly from orbit. But orbital sensors mostly detect the regolith that blankets the Moon. But the regolith is typically mixed and difficult to interpret.

Because Chang’e-3 landed on a comparatively young lava flow, the regolith layer was thin and not mixed with debris from elsewhere. Thus it closely resembled the composition of the underlying volcanic bedrock. This characteristic made the landing site an ideal location to compare in situ analysis with compositional information detected by orbiting satellites.

“We now have ‘ground truth’ for our remote sensing, a well-characterized sample in a key location,” said Dr. Bradley L. Jolliff, the Scott Rudolph Professor of Earth and Planetary Sciences at Washington University in St. Louis. He is a participant in an educational collaboration that helped analyze Chang’e-3 mission data.

“We see the same signal from orbit in other places, so we now know that those other places probably have similar basalts,” Jolliff said of the findings.

The basalts at the Chang’e-3 landing site also turned out to be unlike any returned by the Apollo and Luna sample return missions.

“The diversity tells us that the Moon’s upper mantle is much less uniform in composition than Earth’s,” Jolliff said. “And correlating chemistry with age, we can see how the Moon’s volcanism changed over time.”

The Moon, thought to have been created by the collision of a Mars-sized body with the Earth, began as a molten or partially molten body that separated as it cooled into a crust, mantle and core. But the buildup of heat from the decay of radioactive elements in the interior then remelted parts of the mantle, which began to erupt onto the surface some 500 million years after the Moon’s formation, pooling in impact craters and basins to form the maria, most of which are on the side of the Moon facing the Earth.

Basalts returned by earlier missions had either a high titanium content or low to very low titanium. But measurements made by an alpha-particle X-ray spectrometer and a near-infrared hyperspectral imager aboard the Yutu rover indicated that the basalts at the Chang’e-3 landing site are intermediate in titanium, as well as rich in iron, said Dr. Ling Zongcheng, associate professor in the School of Space Science and Physics at Shandong University in Weihai, and first author of the paper.

Titanium is especially useful in mapping and understanding volcanism on the Moon because it varies so much in concentration, from less than 1 weight percent TiO2 to over 15 percent. This variation reflects significant differences in the mantle source regions that derive from the time when the early magma ocean first solidified.

Minerals crystallize from basaltic magma in a certain order, explained Dr. Wang Alian, research professor in Earth and planetary sciences in Arts & Sciences at Washington University. Typically, the first to crystallize are two magnesium- and iron-rich minerals (olivine and pyroxene) that are both a little denser than the magma, and sink down through it, then a mineral (plagioclase feldspar), that is less dense and floats to the surface. This process of separation by crystallization led to the formation of the Moon’s mantle and crust as the magma ocean cooled.

The titanium ended up in a mineral called ilmenite (FeTiO3) that typically does not crystallize until a very late stage, when perhaps only five percent of the original melt remains. When it finally crystallized, the ilmenite-rich material, which is also dense, sank into the mantle, forming areas of Ti enrichment.

“The variable titanium distribution on the lunar surface suggests that the Moon’s interior was not homogenized,” Jolliff said. “We’re still trying to figure out exactly how this happened. Possibly there were big impacts during the magma ocean stage that disrupted the mantle’s formation.”

The article can be found at: Ling et al. (2015) Correlated Compositional and Mineralogical Investigations at the Chang′e-3 Landing Site.


Source: Washington University in St. Louis.
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