China's Yutu rover revealed new information about the lunar surface

Jade Rabbit provides first data on lunar rock since Apollo

Data from China’s Jade Rabbit lunar rover has revealed the first new "ground truths" about the geology of the Moon since America’s Apollo programme and Russia’s Luna rover in the 1970s.

While satellites have been extensively used to study the lunar surface from the Moon’s orbit in the past decades, the landing of the Chinese Chang'e-3 probe in 2013 - which deployed the Yutu rover, aka Jade Rabbit - allowed the scientists to take a much closer look.

New data published in the latest issue of the journal Nature Communications have shown that the lunar surface is much less uniform than previously thought as the rocks studied by Yutu were completely different from the Apollo-era samples.

"The diversity tells us that the Moon's upper mantle is much less uniform in composition than Earth's," said Professor Bradley L. Jolliff from Washington University in St. Louis, who helped analyse the data.

"Correlating chemistry with age, we can see how the Moon's volcanism changed over time."

While the Apollo and Luna missions landed in areas containing basalts from the peak period of the Moon’s volcanism, which took place some three or four billion years ago, Chang’e 3 landed in the Imbrium basin, which contains much younger lava flows.

As the surface around Yutu’s landing site was covered with only a thin layer of lunar regolith, the rover was able to access bedrock from below.

"We now have 'ground truth' for our remote sensing, a well-characterized sample in a key location," Professor Jolliff said. "We see the same signal from orbit in other places, so we now know that those other places probably have similar basalts."

Satellites used to study lunar surface usually cannot see below the regolith and having more detailed data from the surface would help the researchers better interpret their satellite observations.

Surprisingly, data from the alpha-particle X-ray spectrometer and a near-infrared hyperspectral imager aboard the Yutu rover revealed completely different titanium content in the basalts than detected by Apollo and Luna.

While the 40-year-old samples indicated either very high or very low levels of titanium with no intermediate values, Yutu found rocks with medium titanium content which were particularly rich in iron.

"The variable titanium distribution on the lunar surface suggests that the Moon's interior was not homogenised," 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."

Titanium is key in mapping and understanding the Moon's volcanism because it varies in concentration from less than one weight per cent TiO2 to over 15 per cent.

The researchers believe the Moon was created in a collision between the Earth and a Mars-sized object approximately 4.5 billion years ago. Originally, it was a completely molten body that separated as it cooled into a crust, mantle and core. The build-up of heat from the decay of radioactive elements in the interior then re-melted 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 dark planes, most of which are on the side of the Moon facing the Earth.

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