What are causing the Eccentricity of the planets?

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    Eccentricity Planets
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Discussion Overview

The discussion centers on the causes of the eccentricity of planetary orbits within the solar system, exploring the reasons behind varying degrees of eccentricity among the planets, particularly noting the near-circular orbit of Neptune compared to others. The scope includes theoretical considerations of planetary formation and gravitational interactions.

Discussion Character

  • Debate/contested, Conceptual clarification, Exploratory

Main Points Raised

  • One participant questions the logic behind the varying eccentricities of planets, noting that Neptune has a nearly circular orbit.
  • Another participant suggests that impacts from other objects, both inside and outside the solar system, may contribute to the eccentricity of planets, particularly affecting smaller planets.
  • A different viewpoint argues that perfectly circular orbits are not expected due to gravitational tugs from other planets, which would disrupt such orbits over time.
  • It is noted that while most planets have small eccentricities, many exoplanets exhibit highly eccentric orbits, indicating that current models of planetary formation may need adjustments.
  • One participant asserts that gravitational interactions alone can explain the eccentricities, arguing that the solar system's chaotic nature, particularly influenced by Jupiter's mass, leads to non-circular orbits without the need for collisions.
  • Mercury's orbit is highlighted as being significantly affected by its resonance with Jupiter's orbit.

Areas of Agreement / Disagreement

Participants express differing views on the causes of planetary eccentricity, with no consensus reached on whether impacts or gravitational interactions are the primary factors. The discussion remains unresolved regarding the implications for current models of planetary formation.

Contextual Notes

Some assumptions about the stability of orbits and the role of collisions versus gravitational interactions are not fully explored, leaving open questions about the mechanisms driving eccentricity.

Bjarne
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What are causing the Eccentricity of the planets?
When reaching Neptune we have nearly a completely circular orbit.
Why ?
It seems not to be any logic in this !

Mercury 0,20563069
Venus 0,00677323
Earth 0,01670900
Mars 0,09340100
Jupiter 0,04849500
Saturn 0,05550900
Uranus 0,04629600
Neptun 0,00898800
 
Last edited:
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Since the time the solar system was created, there have been lots of impacts onto planets caused by others objects either from outside of inside the system. The impacts are possible cause of the eccentricity.

There's hardly any rule about the list. Just may be it seems to me: the smaller the planet, the easier it can be hit out of its original (nearly) circular orbit (and the tilt as well).
Mercury, Pluto and Mars ...
 
Why should they be perfectly circular? Each planet in the solar system is also experiencing small tugs from all the other planets so a perfectly circular orbit would not last long.
 
Except for Mercury and Pluto, the planets in our solar system have very small eccentricities. Most exoplanets discovered to date have much highly eccentric orbits: circular (or nearly circular) orbits are not the norm. The standard models of planetary formation, which suggests nearly circular orbits will arise, need some tweaking.

Collisions are not needed to explain the eccentricities in our solar system. All that is needed is gravity. Suppose the planets all had perfectly circular orbits. Gravitational interactions among the planets would quickly result in non-circular orbits. Our solar system is not stable. It is chaotic. Jupiter, being by far the most massive, is the largest contributor to this chaotic behavior. Mercury's orbit, for example, has a strong secular resonance with Jupiter's orbit.
 

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