Now we are certain. The solar system was created at least 4 600 000 000 years ago. This has been proven by the samples of lunar rocks collected by the Apollo mission astronomers and by tests on the oldest rocks found on the Earth. Everything began with a gigantic cloud composed of dust and gas - and especially hydrogen. Most scientists believe that, at a certain point, this primordial cloud, due to its own gravitational attraction, began to contract and revolve around itself, like a cosmic top. This formed a slowly turning disk, with a growing mass of matter at the center. Slowly, this mass became so dense, heavy and hot that it triggered a nuclear reaction, transforming it into a star: the Sun. But how were the planets created? Scientists don't agree on this point. Some believe that at a certain period, due to the effect of the rotation, masses of gas and dust broke off from the primordial nebula which, just like the Sun, gradually contracted and condensed to form first the "protoplanets" and then the real planets. Other scientists believe that the dust grains moving inside the primordial cloud began to collide with each other, condensing until forming larger bodies. Then, by gravity, the largest masses attracted the smaller ones until creating a myriad of bodies, called infinitesimal planets, revolving around the center of the system. Additional collisions then caused the larger bodies to "incorporate" the smaller ones, gradually increasing the volume until attaining their current shape and number. The satellites probably were created in the same way: growing from the dust in the cloud until forming solid bodies. Too small to exist independently but too big to join with the other bodies, they were "captured" by the gravitational field of the planets and held in more or less fixed orbits around them. The theory of the "infinitesimal planets" would seem to be a rather good explanation because the larger planets, Jupiter, Saturn, Uranus and Neptune, thanks to their huge dimensions and great distance from the Sun, still have a rocky core with a large amount of the original gaseous materials. Instead, the inner planets, the asteroids and most of the satellites have only been able to retain their rocky cores, which was increased by the cosmic material from the smaller planets, as demonstrated by the large number of impact craters which cover all the solid bodies in the solar system. The comets and several satellites of the outer planets, which consist mainly of ice, would be the "best preserved" remains of the primordial era. If this is an attempt to reconstruct our past, what can we say about the far future? The Sun is almost five billion years old and will continue to exist for another five billion before reaching the final phase like all the other stars with the same mass - an end that will involve all of its planets. The last "days", which in reality will last for millions of years, will be spectacular: first the Sun will expand enormously becoming a gigantic red star that will swallow Mercury, Venus and perhaps even the Earth. But even the rest of the solar system will be "engulfed" to a certain extent by the star. Then, for several thousand years, the Sun will slowly pulsate, expanding and contracting many times until finally expelling its atmosphere into space in concentric shells of gas with a beautiful red and blue fluorescence. Nothing will remain but a core that will slowly become smaller and colder, a star that astronomers call a "white dwarf", surrounded by planets which have become dead and frozen after the maelstrom of fire. But perhaps our far-off descendants will have already left the condemned system in search of other younger worlds on which to live. And they will have made good use of the experience from the early space adventures which for the last thirty years have allowed us to break away from our planet for the first time and to probe the mysteries of the space that surrounds us. The first small step, but one that already offers good results and surprising discoveries.
Now we are certain. The solar system was created at least 4 600 000 000 years ago. This has been proven by the samples of lunar rocks collected by the Apollo mission astronomers and by tests on the oldest rocks found on the Earth. Everything began with a gigantic cloud composed of dust and gas - and especially hydrogen. Most scientists believe that, at a certain point, this primordial cloud, due to its own gravitational attraction, began to contract and revolve around itself, like a cosmic top. This formed a slowly turning disk, with a growing mass of matter at the center. Slowly, this mass became so dense, heavy and hot that it triggered a nuclear reaction, transforming it into a star: the Sun. But how were the planets created? Scientists don't agree on this point. Some believe that at a certain period, due to the effect of the rotation, masses of gas and dust broke off from the primordial nebula which, just like the Sun, gradually contracted and condensed to form first the "protoplanets" and then the real planets. Other scientists believe that the dust grains moving inside the primordial cloud began to collide with each other, condensing until forming larger bodies. Then, by gravity, the largest masses attracted the smaller ones until creating a myriad of bodies, called infinitesimal planets, revolving around the center of the system. Additional collisions then caused the larger bodies to "incorporate" the smaller ones, gradually increasing the volume until attaining their current shape and number. The satellites probably were created in the same way: growing from the dust in the cloud until forming solid bodies. Too small to exist independently but too big to join with the other bodies, they were "captured" by the gravitational field of the planets and held in more or less fixed orbits around them. The theory of the "infinitesimal planets" would seem to be a rather good explanation because the larger planets, Jupiter, Saturn, Uranus and Neptune, thanks to their huge dimensions and great distance from the Sun, still have a rocky core with a large amount of the original gaseous materials. Instead, the inner planets, the asteroids and most of the satellites have only been able to retain their rocky cores, which was increased by the cosmic material from the smaller planets, as demonstrated by the large number of impact craters which cover all the solid bodies in the solar system. The comets and several satellites of the outer planets, which consist mainly of ice, would be the "best preserved" remains of the primordial era. If this is an attempt to reconstruct our past, what can we say about the far future? The Sun is almost five billion years old and will continue to exist for another five billion before reaching the final phase like all the other stars with the same mass - an end that will involve all of its planets. The last "days", which in reality will last for millions of years, will be spectacular: first the Sun will expand enormously becoming a gigantic red star that will swallow Mercury, Venus and perhaps even the Earth. But even the rest of the solar system will be "engulfed" to a certain extent by the star. Then, for several thousand years, the Sun will slowly pulsate, expanding and contracting many times until finally expelling its atmosphere into space in concentric shells of gas with a beautiful red and blue fluorescence. Nothing will remain but a core that will slowly become smaller and colder, a star that astronomers call a "white dwarf", surrounded by planets which have become dead and frozen after the maelstrom of fire. But perhaps our far-off descendants will have already left the condemned system in search of other younger worlds on which to live. And they will have made good use of the experience from the early space adventures which for the last thirty years have allowed us to break away from our planet for the first time and to probe the mysteries of the space that surrounds us. The first small step, but one that already offers good results and surprising discoveries.
