What are the theories about solar system and the sun and its family?
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About 5 billion years ago there was a large clound, many light years in size, made of of molecules and atoms from the debris of a star that went supernova. That molecluar cloud started to contract by its own gravity. As the center of the cloud got more dense, it's gravitational attraction increased and more and more stuff started condensing toward the center, the core of this contracting molecular cloud. It is a law of thermodynamics that the greater the weight on the core, the greater the pressure on the core. The greater the pressure, the higher the temperature. The core of that condensing molecular cloud got hotter and hotter. When it reached 10 million degrees above absolute zero (10,000,000 K), atomic nucelei (protons) were moving so fast that they were able to overcome the repulsive force between two positively-charged protons. The protons were able to overcome the strong nuclear force, and in doing so, they slammed together, fusing with each other and releasing a tremendous amount of energy in the process. These two atomic nuclei then slammed into another pair of atomic nuclei, emitting a proton, an electron, a positron, a neutrino, and a lot of energy in the form of gamma rays. These paired nuclei slammed into another set of paired nuclei, fusing together and emitting a proton, electron, positron, neutrino, and a gamma ray (extremely high energy light). Those triple nuclei, a helium-3 nucleus, slammed into another triplet, emitting even more enegy and maked a helium atom. Four protons of hydrogen end up as a helium-4 nucleus, a stable form of helium that weighs slightly less than the four protons that went into making it. That difference in weight, according to the formula E=mc^2, is the energy released. The sun fuses many trillions of tons of hydrogen into helium every second, and voila. -- a star is born. This incredible release of enery from the star's core kept the gravity of in-falling material at bay, and the star reached an "equilibrium" -- the outward pressure from the core from the nuclear fusion (A zillion H-bombs going off every second) kept the inward pressure of the weight of the in-falling gas from compressing the star further. The star will continue to fuse hydrogen into helium in its core until it runs out of hydrogen fuel. In the case of our sun, it has been doing this for about 5 billion years and has enough hydrogen "fuel" to keep doing it for another 5 billion years. Around this newborn sun there are the remants of a molecular cloud, molecules and atoms left over from the stuff of an exploding star, a star that went supernova, in the case of our solar system. Our Earth has elements in it that could only have been created by a supernova. These molecular cloud remnants, parts of which have condensed as well but weren't big enough to exert so much pressure on their cores as to ignite nuclear fusion, but some are big enough, like Jupiter, Saturn, etc., to be glowing red-hot in their cores. These hot balls of dense materials were bombarded by smaller fragments, absorbing those fragments and getting larger and larger. As they cooled, they became solid bodies, planets in our solar system. Our solar system's planets were sourrounded by the now-glowing gas from the molecular cloud because the radiation from the sun was ionzing these gases in the cloud (stripping the gases' atoms of electrons). That makes the gas glow. So, as I said, our future planet is orbiting the sun in this gaseous glowing medium, aptly-named a "planetary nebula." We can see other planetary nebulae in our galaxy, so this is something that tends to happen everywhere. At some point, the sun released a burst of energy, called the T-tauri wind, that swept all the gases and loose junk way beyond Pluto, and that left over stuff has been discovered, named the "Oort Cloud" after the Dutch astronomer that discovered it. The Oort Cloud is where comets come from. The inner "rocky planets" -- Mercury, Venus, Earth and Mars, are thought to be rocky because they are close to the sun and the sun's radiation has blown away much of the gas surrounding them. Jupiter is pretty far away, and the sun wasn't able to dissipate the gases. Jupiter is a dense ball of gas condensed from the original molecular cloud. Jupiter is a "failed star." If it were bigger, it would be no different from the sun, it would fuse hydrogen in its core. Same goes for Saturn, Uranus and Neptune. Pluto is rocky, for some reason, and is considered by some to be part of the debris from the Oort Clour. Hope I haven't bored you too much.
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