Sometimes fresh interplanetary discoveries can be made right next door. China's Chang'e 3 rover has found evidence of a new type of basaltic rock in one of the dark basins on the moon.
The findings, published in the journal Nature Communications, focus on a geologically young region of the moon's surface – and shed fresh light on the evolution of our nearest neighbor.
"We recognize a new type of lunar basalt with a distinctive chemical properties and mineral assemblage compared with the samples from Apollo and Luna, and the lunar meteorites," lead author Zongcheng Ling, a planetary scientist at Shandong University in China, said in an email. "These newly characterized basalts reveal a more diverse moon than the one that emerged from studies following the Apollo and Luna missions."
The moon might be the most familiar of celestial objects, but there's still a whole lot we don't know about our nearest neighbor in space. Though ground telescopes and lunar orbiters have sent back reams of data about the moon's surface and composition, neither NASA nor Russia has sent a rover back to the moon in several decades, with the U.S. focusing on more distant worlds such as Mars. So the rocks examined, and in some cases brought back, by these missions have served to corroborate the findings from orbiting missions.
Both views are understandable – after all, the moon is basically a dead barren rock, and more distant worlds, such as Mars, Europa or Enceladus, have a better chance of having life-friendly environments, whether in their past or present. But the moon is thought to be made up of Earth-stuff, born out of the planet's own body after a collision with a Mars-sized missile – and so a fuller understanding of our lunar companion could actually reveal more about the early Earth.
In the meantime, China has thrown its hat into the lunar-visiting ring. The Chang'e 3 orbiter touched down on the moon in late 2013, releasing the Yutu, or Jade Rabbit, rover onto the surface. Although the spacecraft ran into trouble soon after landing, the data sent back has still offered a new look at the surface.
In the new paper, the researchers analyzed soil examined by the Yutu rover at the Chang'e 3 landing site, in a 450-meter-wide crater in the north of the Imbrium basin, an ancient lava floodplain that today can be seen in the larger "eye" on the face of the "man in the moon."
These rocks in lava floodplains are particularly interesting because they offer hints into parts of the moon's past that are hidden from sight, said Noah Petro, a lunar geologist at NASA Goddard Space Flight Center in Maryland who was not involved in the study.
"Because it's something on the surface today but it came up from the deep interior ... it also tells us what's going on beneath the surface as well," Petro said.
Yutu used its Active Particle-induced X-ray Spectrometer and Visible and Near-infrared Imaging Spectrometer to study the regolith – soil that the scientists think was recently dug out of the ground by an impact on the surface. Since that crater is relatively fresh, the soil must be fresh as well, as-yet unmixed with other debris on the lunar surface. So the researchers study this soil to understand what the subsurface of the moon looked like.
Based on the chemicals found within the dark solidified lava (known as basaltic rock), the scientists concluded that the composition of this mare (the dark basaltic plains on the moon) was quite different from the rocks in previously sampled maria. However, the results did match what remote sensing missions, such as those in orbit, were indicating about this particular area.
"It's a really satisfying result because it in some ways validates our interpretation of remote sensing data," Petro said. "By getting this ground truth of what the composition is at this one spot, it helps us better understand the remote data."
And in the rock material examined in this spot – an area that's roughly 3 billion years old – the researchers discovered a surprising mix of chemical abundances, relatively rich in titanium dioxide and also in the mineral olivine (a magnesium iron silicate). In all likelihood, the basaltic rocks probably developed late in the history of the magma ocean that seeded them.
"We think the Moon's surface and interior are more complex than we ever thought," Ling said. "Our findings provide some new constraints on some of the youngest lunar volcanisms and the mantle evolution histories."
The moon would have looked slightly different 3 billion years ago than it does today, Petro said, with a few warm spots left on its mostly cooled surface.
"If you were a time traveler and went back ... you would have seen areas glowing with small volcanic eruptions," Petro said. A few of the small but signature craters pocking its surface would not yet exist.
There are still plenty of unanswered questions about this new lunar basalt that Ling says scientists are hoping to answer by continuing to study the basalts using data from other lunar explorers and meteorites – chunks of the moon that fall to Earth.
"We will also look forward for future lunar mission (like the sample return mission by Chang'e-5) which can help to resolve these puzzles," Ling added.