Il Yutu-2 rover of the Chinese mission Chang'E-4 identified two intact spheres of translucent glass on the far side of the moon. The sighting, captured by the rover's panoramic camera, could lead to important discoveries about the history of the Moon, the composition of its mantle and the impact events on its surface.
A lunar material
At the moment there is no reliable data on the composition of the lunar glass spheres.
The presence of this material on the Moon, however, is anything but extraordinary. Small glass spherules are very common on the satellite surface.
In fact, they originate when silicates are subjected to high temperatures. The glass deposits were formed both during explosive eruptions, due to the volcanic activity of the Moon, and as a result of the heat generated by the impact of smaller objects, such as meteorites.
Parallelisms with the Apollo 16 mission
What is surprising about the globes discovered by Yutu-2 is the size. Lunar glass spherules generally do not exceed one millimeter in diameter. While those identified by the Chinese rover vary from 15 to 25 millimeters.
Spheres similar in size were recovered on the visible part of the Moon during the Apollo 16 mission. The proximity to a crater revealed its origin, the result most likely of an impact.
An indicative shine
A similar event may have produced the globes captured by the rover's onboard camera, which were also found near new impact craters. However, it is possible that these spherules were already present on the lunar soil and that the collision only brought them back to the surface.
The objects found on the hidden side of the satellite present, however, a macroscopic difference compared to those of the Apollo 16 mission. The former are characterized by a sheen vitrea and they result translucent or semi-transparent, unlike the latter which are mostly dark, opaque and rich in clasts.
The hypothesis of the researchers
It is precisely the brightness that makes us lean towards a different origin. As posted on Science Bulletin, it is in fact probable that the dark side spheres of the Moon originated from a volcanic glass called anorthosite, which melted again due to an impact, re-solidifying into translucent round globes.
This hypothesis would relate these lunar objects with some terrestrial formations called tektites.
Towards new discoveries
Pending a more accurate study on the composition of these translucent globes, the hypothesis just described would suggest a consistent presence of these spheres along the entire lunar plateau.
Their sampling will therefore be essential to reconstruct the history of the initial impact of the Moon.
Sources: focustech.it, sciencealert.com
Image source: Science China Press