The crust of our satellite is much more complex than was thought after the US and Soviet missions. There is no tectonics, but there is evidence of explosive eruptions: how is this possible? In 2013, the Chinese Space Authority, CNSA, sent a probe to the moon with a small rover on board. The probe, called Chang'E-3, is happily moored at the expected point, in the Mare Imbrium, one of the largest lunar craters that a hypothesis claims has been filled by huge lava eruptions that date back to around 3.8 billion years ago. Chang'E-3 deposited the rover called Yutu on the ground, which traveled several hundred meters around its base. Then the wheels stopped, a few tens of meters from the probe, and it has remained there to this day. However, Yutu managed to complete many of the experiments that were part of the mission and still today he is partially in a position to use his tools: among these, a radar capable of sounding up to the considerable depth of 400 meters. Below: a selection of photographs of the surface of the Moon around the probe and the rover (click on the images for maximum enlargement), distributed by CNSA and NASA. Explosive eruptions. According to the results obtained so far and published in Science, it appears that the Moon's subsoil is much more complex than what was known after the Apollo missions and the Russian missions. In fact, it seems that the most superficial part of the crust is made up of various layers of rock (up to nine have been counted) which differ in the type of lavas emitted. A completely unexpected discovery, which suggests that the volcanic eruptions that have occurred over time have not only emitted basaltic material (similar for example to most of the eruptions of Etna), but also pyroclastic material (similar to that of Vesuvius) , indicating that in the distant past of the Moon there were also violent explosive eruptions. It is an important discovery from a geological point of view, because until today it was thought that most of the gases had escaped during the cooling of the Moon and that, therefore, explosive eruptions could not have occurred. But if there have been explosive eruptions, it means that many gases have been stored inside our satellite, and this must make us think about the cooling mechanism of the Moon. In this regard, Long Xiao, of the China University of Geosciences in Wuhan, said: «Yutu has allowed us to discover two important things: the first, that the most important volcanic events occurred towards the end of the history of lunar volcanism; the second, that the eruptions were not only effusive, but also explosive ". Now it will be necessary to understand how violent volcanic eruptions have triggered: on Earth they occur in the vicinity of the subduction zones (i.e. the clash between the plates). On the Moon, however, there is no tectonics, therefore there must be another mechanism, yet to be discovered, capable of triggering the phenomenon.