China’s Yutu Rover Found a New Kind of Moon Rock

January 11, 2016 | Elizabeth Knowles

China's Yutu (Chang'e-3) moon rover
Photo credit: Joel Raupe (CC BY-NC-SA 2.0)

It’s nothing like the rocks brought back during the Apollo missions.

Between 1969 and 1972, Astronauts from six Apollo missions brought back 842 pound (382 kilograms) of rock from six different locations on the moon. Around the same time, space probes sent as part of the Soviet Union’s Luna missions returned ¾ of a pound (300 grams) of rock from three more locations. These rocks were used to study the early history of the Mmoon and to better understand how our solar system formed.

In 2013, almost a half-century after the first moon landing, the Chinese space administration (CNSA) sent Chang'e-3, an unmanned soft-landing space probe, to further explore our nearby celestial body.

Since the end of the Apollo/Luna era, lunar exploration has been conducted from probes orbiting the moon. From that height, sensors can detect the regolith — a layer of dust, dirt, and fragmented rock — that covers the surface of the moon, but not what lies beneath it.

Chang’e-3 touched down on the northern part of the Imbrium basin, a lava-filled basin that we can see from Earth. The landing site was a smooth flood basalt plain near a fairly fresh impact crater that has since been named the Zi Wei crater. The lander was accompanied by its rover, Yutu, and the exciting thing about this plain is that it contains excavated bedrock from below the regolith for the rover to study.

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The interesting discovery made by Yutu is that the basalts found at the landing site aren’t anything like the ones found in Apollo and Luna samples. "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."

There are many theories about how our moon came to exist, but the main one is that it was created from a collision between Earth and a Mars-sized body. It would have begun as a molten body and then cooled down. As the decay of radioactive elements in the interior created an excess of heat, parts of the mantle would have re-melted and erupted at the surface 500 million years later. This would have formed the impact craters and basins that our moon is so well known for.

The Apollo and Luna missions targeted rock samples from 3 – 4 billion years ago, whereas the new ones aren’t as old — 3 billion years or younger. The original samples had either very high or very low levels of titanium. These new samples, on the other hand, fill in the gap with intermediate levels of titanium and are also rich in iron according to Zongcheng Ling, PhD, associate professor in the School of Space Science and Physics at Shandong University in Weihai, and first author of the paper.

The amount of titanium in the basalt can be used to map and understand the moon’s history and its volcanic action. The different concentrations indicate various source regions from when the early magma ocean first solidified.

"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."

There is still much to learn about the history of our moon and its geology. More probes and data will be needed to get a complete analysis. Maybe humans will even return someday to do the work in person!

Based on information provided by Washington University in St. Louis.

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