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The "life cycle" of the Sol Nebula is more or less similar to that of other solar nebulae.
Early solar nebulae (in the history of the universe) were formed of hydrogenhydrogen helium H Li Full table General Name, Symbol, NumberHydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1 , s Density, Hardness 0. 0899 kg/m3, NA Appearance colorless Atomic properties Atomic weight 1. 00794 amu Atomic radius (ca, heliumHelium is a colorless, odorless, tasteless chemical element, one of the noble gases of the periodic table of elements. Its boiling and melting points are the lowest among the elements; except in extreme conditions, it exists only as a gas. The second most and lithiumThis article is about Lithium, the element. For the article on mood-stabilizing drugs, see Lithium salt. Lithium is the chemical element with symbol Li and atomic number 3. In the periodic table, it is located in group 1, among the alkali metals. Lithium; while later stars were formed of heavier elements. As the Sol system is comparatively rich in these heavier elements, it can be argued that this system did not emerge directly from the " Big BangIn astrophysics, the term Big Bang is used both in a narrow sense to refer to the interval of time roughly 13. 7 billion years ago when the photons observed in the microwave cosmic background radiation acquired their black-body form, and in a more general".
This nebula had an initial diameterIn geometry, a diameter of a circle is any straight line segment that passes through the center and whose endpoints are on the circular boundary, or, in more modern usage, the length of such a line segment. When using the word in the more modern sense, on of 100 AUThe astronomical unit AU is a unit of distance, approximately equal to the mean distance between Earth and Sun. The currently accepted value of the AU is 149,597,870,691+-30 metres (about 150 million kilometres or 93 million miles). Earth's orbit is not a and a mass of ~200-300% that of Sol's current mass. Over time, gravity caused the cloud to condense and, as densityFor other meanings of density, see density (disambiguation Density (symbol: rho Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass div and pressure increased, a protostar emerged. The early system was heated, not by fusion, but by friction. Due to the conservation of angular momentum, the nebula did not fully collapse upon itself, and thus protoplanetary discs emerged, in orbit, around the protosun.
Within this system, heavier elements tended to fall more towards the center (clumping into planetesimals and protoplanets). In addition, the outer part of the solar nebula cooled off (if it was ever hot to begin with) and, thus, ice and combustible gases were able to "survive". As a result, the inner planets are formed of minerals, while the outer planets are more gaseous/icy.
At some point, the heat within the protosun reached such a level that thermonuclear reactions began to occur. At this point, a "true" star was "born". The protostar lasted for ~100M years and the cycle was completed at about the same time the innermost planets had developed; this was ~4.6B years ago. Although the moons existed, they were not yet orbiting planets; this would occur over the next 800M years.