How do planets form?

In the middle of the 18th century (1755), Emanuel Kant imagined the birthplace of the planets as a flattened disk of gas and dust orbiting a young star, which is now commonly referred to as the protoplanetary disk (PPD) Referred.The first mathematical description was made in 1796 by Pierre-Simon Laplace.
PPD’s are caused by the gravitational collapse of part of a molecular cloud during the formation of a star.Molecular clouds consist mostly of gas (approx. 99%), especially hydrogen and helium, while only a small part (approx. 1%) solid particles, mainly amorphous carbon and silicate compounds. If the density exceeds, or the mass in a certain volume of the molecular cloud a critical value (‘Jeans mass/criterion’), this part of the cloud collapses due to its own gravity. During such a collapse, the largest amount of material (up to 99.9%) is concentrated in the gravitational center together, while the rest due to the preservation of the torque one around the center, respectively the young star rotating disk.

It can be assumed that the temperature in the PPD rotating around the young sun was initially high enough to evaporate most of the solid particles and to highly homogenize the existing material; isotope chemical studies on primitive meteorites and the discovery of so-calledPresolar minerals in such meteorites, however, prove that neither damping nor homogenization took place completely.

A distinction must be made between the formation of gas planets and terrestrial planets.Since I have heard/read little about the formation of gas planets so far, here only so much: the development mechanisms are, to my knowledge, very similar to those of the formation of stars, except that the accumulated mass is not sufficient to cause fusion reactions at the core. Initiate. Here is therefore only a little bit for the formation of terrestrial planets:

If the temperature of the PPD falls, the material begins to condense.The first solid bodies that form in this way are oxides and silicates of calcium and aluminuim, so-called CAI’s (calcium-aluminium-rich inclusions). CAI’s can often be found in primitive meteorites and are among the oldest known materials in the solar system. The Pb-Pb data from nine CAI’s from the Allende meteorite define an isochrone that yields an age of 4,566 +/- 2 Gy; this time marks the ‘canonical’ start of the solar system.

The common theory of planet formation now consists of four steps:

(1) Collisions of microscopic particles lead to the formation of meter-sized aggregates; this process takes about 10 ky and is strongly influenced by interactions with the solar nebula.

(2) Collisions between these aggregates lead to the formation of kilometer-sized (10e12 – 10e18 g) planetesimals.However, the transition from meter-to-mile-sized bodies is not well understood and both steps are also happy to be combined into a single step. As soon as the bodies cross the kilometer limit, their further development is no longer influenced by the solar nebula, but rather by gravitational interactions.

(3) Gravitative interactions between planetesimals lead to the accumulation of approximately Mars-sized (10e26 – 10e27 g) planetary embryos; this process takes about 100 ky.

(4) ‘Giant Impacts’ (grippy German translation is difficult to find) between the planetary embryos eventually lead to the formation of terrestrial planets (10e27 – 10e28 g). The planetary embyros are located on intersecting orbits, and whenever two Embyros collide, they join together to form a larger body.This process continues until a few isolated planets remain in stable orbits (approximately 100 My).

In two works by Halliday et al. (2000) and Canup & Agnor (2000) (both in: R.M. Canup & K. Righter, Origin of the Earth and Moon, 2000.) it can be read that the formation of terrestrial planets is strongly stochastic and much more chaotic and more violent than previously suspected.This means that dynamic models of planet formation with almost identical starting conditions can produce a variety of different, final planetary configurations.

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