In recent years, some astronomers have proposed that the initiating force in the formation of our Solar System should be the explosion of a supernova.
One can imagine that a vast cloud of dust and gas that would already exist, relatively unchanged, for billions of years, would have advanced into the neighborhoods of a star that had just exploded like a supernova.
The shock wave of this explosion, the vast burst of dust and gas that would form as it passes through the almost inactive cloud that I mentioned would compress this cloud, thus intensifying its gravitational field and initiating the condensation that comes with Star formation
If this was the way the Sun was created, what happened to the planets? Where did they come from? The first attempt to get an answer was advanced by Immanuel Kant in 1755 and, independently, by the French astronomer and mathematician Pierre Simón de Laplace, in 1796. Laplace's description was more detailed.
According to Laplace's description, the huge cloud of contracting matter was in the rotary phase at the beginning of the process. Upon contracting, its rotation speed was increased, in the same way that a skater spins faster when he picks up his arms. This is due to the "angular momentum conversion." Since this moment is equal to the speed of the movement by the distance from the center of rotation, when such distance decreases, the speed of the movement is increased in compensation.
According to Laplace, as the speed of rotation of the cloud increased, it began to project a ring of matter from its equator, in rapid rotation. This somewhat decreased the angular momentum, so that the speed of rotation of the remaining cloud was reduced; but by continuing to contract, he again reached a speed that allowed him to project another ring of matter. Thus, the Sun was leaving behind a series of rings (clouds of matter, in the form of donuts), which slowly condensed, to form the planets; Over time, they expelled, in turn, small rings, which gave rise to their satellites.
Because of this view, that the Solar System began as a cloud or nebula, and since Laplace pointed to the Andromeda Nebula (which was then not known to be a vast galaxy of stars, but was believed to be a cloud of dust and gas in rotation), this suggestion has come to be known as a nebular hypothesis.
The nebular hypothesis de Laplace seemed to fit very well with the main features of the Solar System, and even some of its details. For example, Saturn's rings could be those of a satellite that had not condensed since, by joining together, a satellite of respectable size could have formed. Similarly, the asteroids that revolved, in a belt around the Sun, between Mars and Jupiter, could be condensations of parts of a ring that would not have joined together to form a planet. And when Helmholtz and Kelvin elaborated theories that attributed the energy of the Sun to its slow contraction, the hypotheses seemed to fit perfectly again to Laplace's description.
The nebular hypothesis remained valid for most of the nineteenth century. But before it ended it began to show weaknesses. In 1859, James Clerk Maxwell, when analyzing mathematically the Saturn's rings, concluded that a ring of gaseous matter thrown by any body could only condense into an accumulation of small particles, which would form such rings, but could never form a solid body, because gravitational forces would fragment the ring before its condensation will materialize.
The problem of angular momentum also arose. It was that the planets, which constituted only slightly more than 0.1% of the mass of the Solar System, contained, however, 98% of their angular momentum! In other words: the Sun retained only a small fraction of the angular momentum of the original cloud.
How was almost the entire angular momentum transferred to the small rings formed from the nebula? The problem is complicated to verify that, in the case of Jupiter and Saturn, whose satellite systems give them the appearance of miniature solar systems and that they have presumably been formed in the same way, the central planetary body retains most of angular momentum.
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