The Yutu-2 mission has made another fascinating find on the far side of the Moon. In the journal Science Bulletin, a team of Chinese researchers describes the discovery of small translucent glass balls sparkling in the middle of the dust. What is it precisely?
On January 3, 2019, China marked the spirits by gently landing on the dark side of the Moon. The lander and its rover Yutu 2 are currently still positioned in the Von Karman crater, at the south pole.
During its journey (more than 850 meters traveled), the 140-kilo rover came across a few surprises, including strange small stones, sometimes very elongated, sometimes very square. Eventually, the Chinese scientists claimed that it was just simple rocks excavated following the impact of meteorites. More recently, the rover came across another surprise: glass beads.
Translucent Marbles on the Moon
These objects are not new to the Moon. This type of material is formed when the silicate is subjected to high temperatures. However, volcanism (in the past) and meteor impacts can generate enough heat to cause glass to form in place.
These small spherules nevertheless remain interesting, because they are a little different from those spotted on the other lunar side during previous missions. The latter tend to be less than a millimeter in size, although some (spotted as part of the Apollo 16 mission) measured up to forty millimeters. According to the Chinese team led by planetary geologist Zhiyong Xiao, of the Chinese Academy of Sciences, the glass beads identified by Yutu-2 here measure fifteen to twenty-five millimeters in diameter.
Additionally, the spherules on this far side appear to be translucent or semi-transparent and have a vitreous luster, unlike those previously identified.
What origin ?
All were found near new craters, which could suggest they formed during lunar meteor impacts. However, it remains possible that they were already present under the surface before being simply excavated by impacts.
However, the researchers believe the most likely explanation is that they formed from volcanic glass called anorthosite that melted again from impacts, later reforming into translucent beads. This could make objects the lunar equivalent of Earth formations called tektites. They are small glassy pebble-sized objects formed when earth material melts, vaporizes in the air, then hardens before falling back to the ground.
If they are indeed lunar tektites, they could be quite common on the lunar surface. “As the first discovery of macroscopic, translucent glass globules on the Moon, this study predicts that such globules should be abundant across the lunar highlands, providing promising sampling targets to reveal the history of early impacts of the Moon,” write the researchers. However, we can’t know for sure until Yutu-2 gets composition data.