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Physics, Astronomy & Cosmology / Re: Why are the planets such different sizes - and in no particular size sequence?
« on: 08/03/2016 11:38:13 »
The answer is complex, but this is a simplified version.
Planets form from a collapsing cloud of gas and dust. They are almost incidental, since most of the mass goes into the proto-star. The rest of the dust and gas form a flat disc around the star in which particles condense and coalesce.
As the star warms up the temperature in the disc prohibits ices from forming in the inner part of the system, so that rocky planets are formed. Further out ices can condense and coat any rocky cores that are formed. Stellar activity also drives gas away from the inner part of the system (and eventually all of it), but the outer rocky cores can attract some of this gas.
Thus we end up with small rocky planets in the inner system and large gaseous and icy planets with rocky cores in the outer system. During this process planets can move around a lot as a consequence of interaction with the disc and mutual gravitational effects. Some are lost into the parent star, some are ejected from the system and some swap places.
Planets form from a collapsing cloud of gas and dust. They are almost incidental, since most of the mass goes into the proto-star. The rest of the dust and gas form a flat disc around the star in which particles condense and coalesce.
As the star warms up the temperature in the disc prohibits ices from forming in the inner part of the system, so that rocky planets are formed. Further out ices can condense and coat any rocky cores that are formed. Stellar activity also drives gas away from the inner part of the system (and eventually all of it), but the outer rocky cores can attract some of this gas.
Thus we end up with small rocky planets in the inner system and large gaseous and icy planets with rocky cores in the outer system. During this process planets can move around a lot as a consequence of interaction with the disc and mutual gravitational effects. Some are lost into the parent star, some are ejected from the system and some swap places.
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