A great collision between the Earth and Theia, a ghost planet: explaining the origin of the Moon
The impact seems to be the right hypothesis for understanding how our natural satellite formed and where the planet responsible for the collision came from
Perhaps the mystery of the Moon's origin has been unravelled, thanks to a paper published in recent days in the leading scientific journal Science. The impact between the Earth and a large celestial body, from which the Moon was formed, now seems even more the right hypothesis for understanding how our natural satellite was formed and where the planet responsible for the impact, from which it emerged completely destroyed, came from.
It is a long-standing mystery that now, thanks to the patient work of the research team led by the University of Chicago, USA, and the Max-Planck-Institut für Sonnensystemforschung, Germany, is thought to have been solved.
Let us proceed in order: the beautiful Moon, which illuminates our nights when it is full, is a somewhat peculiar satellite. In the meantime, it is lonely, it is the only one on Earth, and it is also very large compared to the planet it orbits: its diameter is about a quarter of that of the Earth, and its mass is about one-eightieth of that of the Earth. It seems little, but it is a lot relative to the planet it is orbiting. The fact that we always see the same face, with a few small periodic oscillations, seems very normal to us, but it is not at all. It is called spin-orbit coupling and, beyond words, it means that very old systems tune like the notes on a guitar and the Moon, therefore, orbits around us at the same time as it rotates around itself. And this is the datum that allows us to say that the Earth-Moon is an 'old' system, more than four billion years old.
We could go on for many pages, but we will stop and return to the scientific article that sheds light on the Moon's genesis, for alongside so many certainties, questions also remain. The main one is: how did this strange couple form?
Many hypotheses have been put forward, the one on which the spotlight has been shining for some time is the cosmic collision: the Earth had just formed in a still young and very violent solar system, with frequent, even gigantic collisions, when it collided with a similar planet the size of Mars. A celestial body therefore smaller than the Earth, with a diameter half that of the Earth, and a mass nine times smaller. Smaller but comparable. One can understand that the collision must have been tremendous, but back then the solar system was full of stray bodies of all sizes, which today have thankfully been reduced to a minimum. Everything that was out of balance with the rest of the system was swept away by collisions, a kind of game of space billiards in which even the Earth got involved.
