Why do small bodies stay in orbit around large bodies?

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Discussion Overview

The discussion revolves around the stability of orbits of small bodies around larger bodies, particularly in the context of gravitational interactions and chaos theory. Participants explore the implications of small changes in gravitational pull due to various factors, including rotation and distance, and how these changes affect orbital dynamics over time.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that even tiny changes in gravitational pull could lead to significant alterations in the orbits of smaller bodies over time.
  • Others argue against this notion, asserting that orbits are generally stable and that small perturbations do not lead to drastic changes in orbital paths.
  • A participant notes that the orbits observed today are stable enough to have persisted over millions of years, with changes being constrained by energy and momentum conservation.
  • There is a mention of the misconception that orbits are highly unstable, with some participants clarifying that even major perturbations typically only reshape orbits rather than cause them to collapse or diverge significantly.
  • Discussion includes the distinction between two-body and n-body systems, with some participants emphasizing the complexity introduced by multiple gravitational interactions.

Areas of Agreement / Disagreement

Participants express differing views on the stability of orbits and the effects of small changes in gravitational forces. There is no consensus on whether tiny changes can lead to significant orbital alterations, indicating an unresolved debate.

Contextual Notes

Participants highlight the need for clarification on what constitutes "tiny" changes in gravitational pull and address common misconceptions about orbital stability. The discussion reflects varying assumptions about the nature of gravitational interactions in both two-body and n-body systems.

Jireat
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I know this sounds like an elementary question with an easy answer.

However, I was thinking about chaos theory. Planets and stars are always changing so that their gravitational pulls towards other objects varies. Shouldn't the tiniest change between the pull of a star and a planet, or a planet and its moon (change due to rotation or distance [elliptical paths]) cause smaller objects to either get increasingly close or increasingly far from the large objects, per unit time?

Thank you in advance!
 
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Jireat said:
Shouldn't the tiniest change between the pull of a star and a planet, or a planet and its moon (change due to rotation or distance [elliptical paths]) cause smaller objects to either get increasingly close or increasingly far from the large objects, per unit time?

No. Why do you think this would be the case?
 
Jireat said:
However, I was thinking about chaos theory. Planets and stars are always changing so that their gravitational pulls towards other objects varies. Shouldn't the tiniest change between the pull of a star and a planet, or a planet and its moon (change due to rotation or distance [elliptical paths]) cause smaller objects to either get increasingly close or increasingly far from the large objects, per unit time?
The orbits you see today are those which happened to be stable enough to survive millions of years. They might be changing slightly over time, but those changes are constrained by energy and momentum conservation, so a planet cannot just fly off.
 
Orodruin said:
No.
Wouldn't you say that it's actually a yes, as long as you give n-body interactions enough time?
 
Bandersnatch said:
Wouldn't you say that it's actually a yes, as long as you give n-body interactions enough time?

I would say the OP deals with a two-body system:
Jireat said:
the pull of a star and a planet, or a planet and its moon
 
Jireat said:
Planets and stars are always changing so that their gravitational pulls towards other objects varies. Shouldn't the tiniest change between the pull of a star and a planet, or a planet and its moon (change due to rotation or distance [elliptical paths]) cause smaller objects to either get increasingly close or increasingly far from the large objects, per unit time?
First: How "tiny" is "tiniest"? Its pretty tiny: you can Google it for Earth.

Second, a lot of people have a misconception about orbits, that they are very unstable and that the slightest perturbation will cause the objects to spiral apart or together. In reality, they are very stable and even a major perturbation will only reshape them: To make two objects that are in a circular orbit crash into each other requires dissipating almost all of the orbital energy. Much less and you just change the shape into a more elliptical orbit.
 

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