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By 10 million years, gas in the protoplanetary disc has been blown away, and outer planet formation is likely complete. [38] 10 million – 100 million years 4.5–4.6 bya: Terrestrial planets and the Moon form. Giant impacts occur. Water delivered to Earth. [2] Main sequence 50 million years 4.5 bya: Sun becomes a main-sequence star. [32] 200 ...
A group of the world's leading planet formation experts decided at a conference in 2006 [8] on the following definition of a planetesimal: A planetesimal is a solid object arising during the accumulation of orbiting bodies whose internal strength is dominated by self-gravity and whose orbital dynamics is not significantly affected by gas drag ...
As a result, astronomers largely abandoned this theory of planet formation at the beginning of the 20th century. According to some, a major critique came during the 19th century from James Clerk Maxwell (1831–1879), who in some sources is claimed to have maintained that different rotation between the inner and outer parts of a ring could not ...
Iwan P. Williams and Alan William Cremin [4] split the models between two categories: those that regard the origin and formation of the planets as being essentially related to the Sun, with the two formation processes taking place concurrently or consecutively, and those that regard the formation of the planets as being independent of the ...
A planet's year depends on its distance from its star; the farther a planet is from its star, the longer the distance it must travel and the slower its speed, since it is less affected by its star's gravity. No planet's orbit is perfectly circular, and hence the distance of each from the host star varies over the course of its year.
The history of planetary science may be said to have begun with the Ancient Greek philosopher Democritus, who is reported by Hippolytus as saying . The ordered worlds are boundless and differ in size, and that in some there is neither sun nor moon, but that in others, both are greater than with us, and yet with others more in number.
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...
Viktor Sergeevich Safronov (Russian: Ви́ктор Серге́евич Сафро́нов) (born Velikie Luki; 11 October 1917 in Russia – 18 September 1999 in Moscow, Russia) was a Soviet astronomer who put forward the low-mass-nebula model of planet formation, a consistent picture of how the planets formed from a disk of gas and dust around the Sun.