Most of the planets in the Solar System have satellites. For example, Mars has two moons, Jupiter 79 and Neptune 14. Some are icy, others rocky, others are geologically active, but there are also those with little or no activity. But how did they get there? Were they all formed the same way? What could you tell us about the origins of our cosmic neighborhood?

You don’t have to go very far for the questions to appear. We’re still not entirely sure how our satellite formed, although the most widely accepted theory is that a body the size of Mars, called Theia, collided with proto-Earth. Our planet ended up being the “eldest son” of this collision, retaining enough heat to become tectonically active.

However, the smaller Moon probably cooled faster and was geologically frozen. However, since the Apollo missions, it is known that there is some activity on the Moon, which conflicts with this explanation. What happens then?

Geological activity
At the moment of the crash, the components of Theia and the prototarth were mixed. Afterward, they quickly parted ways within a few million years. Thanks to the dynamics of the collision that formed the Earth-Moon system, the Earth has capacities to retain volatile substances such as water or gases that make up the atmosphere, and to have enough internal heat to maintain long-term planetary volcanism and tectonics. . Decades of observations have shown that lunar history was much more dynamic than expected, with volcanic and magnetic activity occurring just 1 billion years ago, much later than originally thought.

Most of the planets in the Solar System have satellites. For example, Mars has two moons, Jupiter 79 and Neptune 14. Some are icy, others rocky, others are geologically active, but there are also those with little or no activity. But how did they get there? Were they all formed the same way? What could you tell us about the origins of our cosmic neighborhood?

You don’t have to go very far for the questions to appear. We are still not entirely sure how our satellite formed, although the most widely accepted theory is that a body the size of Mars, called Theia, collided with proto-Earth. Our planet ended up being the “eldest son” of this collision, retaining enough heat to become tectonically active.

However, the smaller Moon probably cooled faster and was geologically frozen. However, since the Apollo missions, it is known that there is some activity on the Moon, which conflicts with this explanation. What happens then?

Geological activity
New research published in “Nature Geoscience” suggests that this is because radioactive elements were distributed in a peculiar way after the catastrophic collision formed the Moon. At the moment of the crash, the components of Theia and the prototarth were mixed. Afterward, they quickly parted ways within a few million years. Thanks to the dynamics of the collision that formed the Earth-Moon system, the Earth has capacities to retain volatile substances such as water or gases that make up the atmosphere, and to have enough internal heat to maintain long-term planetary volcanism and tectonics. . Decades of observations have shown that lunar history was much more dynamic than expected, with volcanic and magnetic activity occurring just 1 billion years ago, much later than originally thought.

And this separation also contributed to the fact that the visible and hidden faces of the Moon are very different. Superficially, on the near side of the Earth, dark and light spots can be seen with the naked eye. The first astronomers called these dark regions “Maria”, which is Latin for “seas”, thinking that they were indeed bodies of water. But using telescopes, scientists were able to discover more than a century ago that these were not actually seas, but rather craters or volcanic features. And, back then, science assumed that the other side, the hidden one, was the same. But no.

The face that hides the origin
In the late 1950s and early 1960s, unmanned space probes launched by the USSR showed the first images from the other side of our satellite, at which point scientists were surprised: it had almost no « seas ». Only 1% of the far side was covered in “maria” compared to 31% for the near side. Also, the crust is thicker, with a different composition on the near side. The surface is also much paler, with fewer basalt spots and covered in craters.

This was interpreted to mean that the basalt flows on the near side covered a large number of craters on the Moon, but why the near side had more volcanic activity than the far side has been a pretty big mystery that lunar scientists have wanted to solve. . Also, there is something more peculiar on the visible side: a geochemically strange region called Procellarum KREEP Terrane.

The mysterious KREEP
By collecting samples from the Apollo missions, scientists quickly discovered that the relative darkness of these patches was due to their geological makeup and, in fact, were attributable to volcanism. They also identified a new type of rock signature that they called KREEP: short for potassium-enriched rock (chemical symbol K), rare earth group elements (REE, which include cerium, dysprosium, erbium, europium, and other elements that are rare in the world). Earth) and phosphorus (chemical symbol P), which was associated with the seas. It also contains elements such as uranium and thorium, whose radioactive decomposition generates heat.

This Procellarum KREEP Terrane appears to be associated with the basalt plains, and its heat-generating properties have been previously shown to have something to do with prominent volcanism on the visible side. In fact, thermal modeling of the lunar interior suggests that the radioactive decay of potassium, thorium, and uranium could have provided a near-side heat source for billions of years.