Planetary orbits -- Why do planets orbit at same “level”?

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Discussion Overview

The discussion centers on the reasons why planets in our solar system orbit the sun in similar orbital planes, exploring the origins of this phenomenon and the dynamics involved. It touches on theoretical aspects of planetary formation and orbital mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that the similarity in orbital planes is due to the heritage of planets originating from a rotating cloud of material that formed a disk around the sun.
  • Others elaborate that the planets' initial positions within this disk constrain them to orbit in a plane unless significantly perturbed by large objects, which is considered rare.
  • A participant introduces the concept of Kozai resonance, noting that bodies with large inclinations are subject to perturbations that can alter their orbits, while those with low inclinations do not experience this effect.
  • There are mentions of specific bodies, such as comet Hale-Bopp, which have high inclination orbits but are not classified as planets, raising questions about the stability of such orbits over time.
  • One post raises the question of whether any multi-planet systems have been confirmed to contain planets orbiting in opposite directions, contrasting with the solar system's planets that all orbit in the same direction.

Areas of Agreement / Disagreement

Participants generally agree on the influence of the initial disk formation on planetary orbits, but there are competing views regarding the role of Kozai resonance and the stability of orbits at different inclinations. The discussion remains unresolved regarding the existence of multi-planet systems with planets in opposite directions.

Contextual Notes

Some assumptions about the nature of perturbations and the specific conditions under which Kozai resonance operates are not fully explored. The discussion also does not resolve the implications of different orbital inclinations for planetary stability.

Josh0768
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TL;DR
Why do planets orbit at same “level”?
Why is it that all of the planets in our solar system (to our knowledge) orbit the sun in such a way that they all go around the sun in roughly similar orbital planes? Why don’t we have planets with orbital planes at significantly different angles?
 
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Heritage of their origin from a rotating cloud of material in the form of a disk.
 
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As BillTre said, the solar system formed from a collapsing cloud of material that collapses into a disk. The center of this disk collapses further to become the Sun, and other areas collapse into proto-planetary bodies. By nature of their initial position as part of this disk, the resulting planets are constrained to closely orbit in a plane unless they are perturbed significantly by planetary-sized objects, which is extremely rare.
 
Also Kozai resonance.
Bodies that orbit at large angle to other bodies are liable to large perturbations that change their orbits to something else.
There are such bodies, like comet Hale-Bopp. But those are long period comets, that rarely enter into inner solar system to get perturbed again. Periodic comets don´ t last on high inclination orbits, and neither would planets.
 
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Josh0768 said:
Summary:: Why do planets orbit at same “level”?

Why is it that all of the planets in our solar system (to our knowledge) orbit the sun in such a way that they all go around the sun in roughly similar orbital planes? Why don’t we have planets with orbital planes at significantly different angles?
Try this to start:



The flattening happened quite early in the solar system's development.
 
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Note that Kozai resonance only operates for large inclinations.
It does NOT operate for low inclination but retrograde objects. Which is why Halley comet is periodic - being at a low inclination orbit, it does not suffer from Kozai resonance. It is only comet sized, though - not a planet.
Of hot jupiters, a third (sic!) orbit retrograde to the rotation of star. How are the conditions about multiplanet systems? Has any multiplanet system yet been confirmed to contain planets orbiting in opposite directions? Solar System planets have been confirmed to orbit in the same direction, but any others?
 

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