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Author Topic: Why do the planets orbit the sun at the distances they do?  (Read 1969 times)

Offline acecharly

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Is there a reason the rocky planets orbit close and the gas giants are further out and is this the case in other observed solar systems?

Cheers
Ace


 

Offline damocles

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The evolution of planetary systems is largely, but not fully understood. A lot of quite complicated factors are involved. But to the very broad thrust of your question, there is a very simple answer.

The question should really be put the other way around -- why are the planets that orbit close rocky? And why can gas giants form further out?

The simple answer is that 90% of the material in the solar system is hydrogen. Planets orbiting close to the sun have lost (nearly all of) their hydrogen quite early in the stages of their formation, while those further out have been able to retain it.

Why has hydrogen been lost from the inner part of the solar system?
(1) It is part of the process of initial planetary formation.
(2) Hydrogen that remained with the original planets has been depleted by solar heating, solar gravitation (and the inadequacy of planetary gravitation at high temperatures), and solar radiation (the solar wind).
 

Offline acecharly

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Ahhh nice answer. I never thought of those. I wondered if it was something to do with mass, similar to if you take a bucket of different sized granules and shake them up for a while they seperate into layers relative to their size.
 

Offline RD

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Q. Why do the planets orbit the sun at the distances they do?

A. looks like resonance ... https://en.wikipedia.org/wiki/Titius-Bode_law#Data
 

Offline acecharly

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ahh interesting ...thanks for finding that out RD, I wonder how this tallys up with other systems. If correct it could help with locating exoplanets.
 

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