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Formation of Planets After BigBang | Article 3

This is Third Article of Origin of Earth.

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Formation of planets after bigbang

The various planets are thought to have formed from the solar nebula,the disc shaped cloud of gas and dust left over from the sun's formation. The currently accepted method by which the planets formed is accretion, in which the planets began as dust grains in orbit around the central protostars. Through direct contact and self organisation, these grains formed into clumps up to 200 meters in diameters, which intern collided to form larger bodies of 10 kilometer in size. This gradually increased through further collisions, growing at the rate of centimeter per year over the course of the next few million years.

Formation of Planets
Formation of Planets

The inner solar system, the region of the solar system inside 4 AU, was to warm for volatile molecules like water and methane to condense, so the planetesimals that formed their cloud only from compounds with high melting points, such as metal and Rocky silicates.these Rocky bodies would became the terrestrial planet.these compounds are quite rare in the universe, comprising only 0.6% of the mass of the nebula, so the terrestrial planets could not grow very large. The terrestrial embryos grew to about 0.05 Earth masses and ceased accumulating matter about 100,000 years after the formation of the sun subsequent collision and mergers between these planet sized bodies allowed terrestrial planets to grow to their present sizes.

When the terrestrial planets were forming, they remained immersed in a disc of gas and dust. The gas was partially supported by pressure and so did not orbit the sun as rapidly as the planets.the resulting drag and, more importantly, gravitational interactions with the surrounding material caused a transfer of angular momentum, and as a result the planet gradually migrated to new orbits.models show that density and temperature variation in the disc govern this rate of migration, but the net Grand was for the inner planets to migrate in word as the disc dissipated, leaving the planets in their current orbits.
The giant planets formed further out, beyond the Frost line, which is the point between the orbits of Mars and Jupiter where the material is cool enough for volatile ice compounds to remain solid. The ices that formed the Jovian planets one more abundant than the metals and silicates that formed the terrestrial planets, allowing the giant planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements. Plantesimals on the Frost line accumulated up to 4 M within about 3 million years.Today, the four giant planets comprise just under 99% of all the mass orbiting the sun. Theorists believe it is no no accident that Jupiter lies just beyond the Frost line. Because the frost-line accumulated large amount of water evaporation from in following ice materials, it created a region of lower pressure that increased the speed of orbiting dust particles and halted their motion towards the sun. Chain effect, the Frost line acted as a barrier that caused material to accumulate rapidly at 5 AU from the sun. This access material coalesced into a large embryo on the order of 10 M, which begin to accumulate and envelope via excretion of gas from surrounding disc at an ever increasing rate. Once the envelope mass became about equal to the solid core mass, growth proceeded very rapidly, reaching about 150 Earth masses 10^5 years thereafter and finally topping out at 318 M. Saturn may owe it's substantially lower mass simply to having formed a few million years after Jupiter, when there was less guess available to consume.

T Tauri stars like the young sun have far stronger stellar winds then more stable, older stars. Uranus and Neptune are thought to have formed after Jupiter and Saturn did, when the strong solar wind had blown away much of the disc material. As a result, those planets accumulated little hydrogen and helium not more than 1 M each. Uranus and Neptune are sometimes referred to as failed cores.the main problem with the formation theories of these planet is the time scale of their formation. At the current locations it would have taken millions of years for their cores to accrete. this means that Uranus and Neptune may have formed closer to the sun—near or even between Jupiter and Saturn —and later migrated or ejected outward. Motion in the planetesimal era was not all in word toward the sun. The stardust sample return from comet wild to has suggested that material from the early formation of the solar system migrated from the warmer inner solar system to the region of the kuiper belt

After between 3 and 10 million years, the young sun solar wind would have cleared away all the gas and dust in a protoplanet traders, blowing it into interstellar space, thus ending the growth of planets.

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