The Beginning of the Solar System

• The Nebular theory is the idea that the solar system originated from a nebula was proposed in 1734 by Swedish scientists and theologian Immanuel Kant.
• Nebular Theory - A hypothesis about how our solar system formed. It suggests that the sun and planets were created when a cloud of dust and gases (a nebula) collapsed under its own gravity.
• According to the nebular hypothesis, the solar system began as a rotating disk of gas and dust around a central protostar. As it cooled, the material condensed into solid particles called planetesimals which eventually coalesced into larger bodies such as asteroids and comets.
• Immanuel Kant, who was familiar with Swedenborg's work, developed the Nebular theory further and published it in his Universal Natural History and History of the Heavens (1755).
• A similar model of the Nebular theory was developed independently and proposed in 1796 by Pierre-Simon Laplace.
• The trouble for Nebular theory is that the sun rotates too slowly for this model to explain.
• Buffon's (1749) Aun-Comet encounter that sent matter to form planet.
• T.C. Chamberlain and F.R. Moultons (1904) Planetesimal Hypothesis involving a star much bigger than the sun passing by the sun and drawing gaseous filaments from both out which planetesimals were formed.
• Otto Schmidt's Accretion theory proposed that the sun passed through a dense interstellar cloud and emerged with a dusty, gaseous envelope that eventually became planets.
• The accretion theory cannot explain how the planets and satellites were formed. The time required to form planets exceeds the age of solar system.
• M.M. Woolfson's Capture Theory is a variation of James Jeans' Near-Collision Hypothesis.
• In the Capture theory, the sun drags from a near proto-planet a filament of material which becomes planets.
• Collisions between proto-planets close to the sun produced the terrestrial planets according to the capture theory.
• Condensation of the protoplanets produced the giant planets according to the capture theory.
• Capture theory also postulates that some of the moons were actually asteroids captured by the planets. Different ages for the sun and planet is predicted by this theory.
• The Protoplanet Hypothesis proposed by Hunter Mcrea (1960) says that a slowly-rotating gas and dust cloud dominated by hydrogen and helium starts to contract due to gravity.
• Protoplanet Hypothesis also postulates that as most of the mass move to the center to eventually become a proto-sun, the remaining materials form a disc that will eventually become the planets and momentum outwards.
• The Planets differ in chemical composition depending on their distance from the sun. Inner planets formed near the center where the temperature is high enough to vaporize compounds except high-temperature metallic silicate minerals in the inner portion of the disk, which explains the composition of the inner planets and outer planets which remained cooler, allowing them to be made of icy and gaseous materials.
• Collision of the planet with a large object produces the moon. This is supported by the composition of the moon that is very similar to the Earth's Mantle according to the protoplanet hypothesis.