# Why do small bodies stay in orbit around large bodies?

• Jireat
In summary, planets and stars will always be changing their gravitational pulls towards each other, but the orbits you see today are those which happened to be stable enough to survive millions of years.
Jireat
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?

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.

## 1. Why do small bodies stay in orbit around large bodies?

Small bodies stay in orbit around large bodies due to the force of gravity. The larger body has a greater mass and therefore exerts a stronger gravitational force, pulling the smaller body towards it.

## 2. What keeps small bodies from crashing into larger bodies?

The velocity of the smaller body in its orbit keeps it from crashing into the larger body. The combination of the gravitational force pulling the smaller body towards the larger body and the velocity of the smaller body creates a balanced circular motion, keeping the two bodies in orbit.

## 3. Do all small bodies stay in orbit around large bodies?

No, not all small bodies stay in orbit around large bodies. The size, mass, and velocity of the smaller body, as well as the distance between the two bodies, all play a role in determining whether the smaller body will stay in orbit or not. If the smaller body has enough velocity, it may escape the gravitational pull of the larger body and continue on its own path.

## 4. How does the shape of an orbit affect the path of a small body?

The shape of an orbit is determined by the velocity and direction of the smaller body. A circular orbit has a constant distance from the larger body, while an elliptical orbit has a varying distance. The shape of the orbit affects the path of the small body by determining how close it will get to the larger body at different points in its orbit.

## 5. Can small bodies have multiple orbits around a single large body?

Yes, small bodies can have multiple orbits around a single large body. This can occur when the smaller body has enough velocity to stay in orbit but also has enough velocity to create a second orbit around the larger body. This is known as a binary system, where two bodies orbit around a common center of mass.

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