# Can gravitational effects create a plane of the ecliptic?

Lots of questions about the why of the plane of the ecliptic, and good answers, but I was wondering about gravitational effects.

If we picture for example, Saturn as being a few degrees above the plane, then Jupiter and Uranus being a few degrees below the plane, would the gravitational pull of each of these planets tend to pull them into the same plane after millions, perhaps billions of years?

Purely gravitational effects: no, because they are conservative and symmetric. The Kozai-Mechanism can cause the planes of the different individual orbits to vary their inclination --- but in a periodic way, oscillating above and below the ecliptic.

Gravity can contribute to forming an ecliptic if you add dissipative effects, like gas-drag from a gaseous/debris disk, or tidal-dissipation.

• It is still gravity forming the plan whether its caused by the star or the Kozai mechanism from other bodies in the plane. as a body orbits a vstar if it wobbles above the plane then gravitational effects from the plane will pull it back down towards the plane until it wobbles below the plane and then gravitational effects from the plane will pull it back up. – Bill Alsept Dec 19 '15 at 19:43
• @BillAlsept, that's the average angular momentum axis of the given 3-body system. – DilithiumMatrix Dec 19 '15 at 19:48

@Bill Alsept: Yes gravity effects this. As the planets orbit the sun they wobble above and below the plane slightly, some more than others. The solar system does the same thing as it orbits our galaxy. I suppose like a pendulum these wobbles are diminishing.

The Rest of the Story: A pendulum slows down because of friction and air resistance (neither of which exist in space, okay there are tidal forces but these are not responsible for defining the ecliptic). So if the wobbles are indeed decreasing, where does the lost energy go? The classical many body system exhibits both "clockwork-like" behavior (yielding planetary motion mostly confined to the ecliptic) as well as "chaotic behavior" (like small objects not confined to the ecliptic being occasionally tossed out of orbit or into the outer Oort cloud thereby absorbing the lost energy). See: https://en.wikipedia.org/wiki/N-body_problem#History Over millions/billions of years the many smaller non-ecliptic objects in the planetary regions may get ejected and the larger ecliptic-confined objects become even more "clockwork-like." Occasionally these non-ecliptic objects return to the inner solar system as long period comets.

• Gravity alone causes the wobble the gradual slowdown would come from title force and Space debris. – Bill Alsept Dec 18 '15 at 23:32
• Yes, gravity is doing it all but the chaotic interactions are what gets rid of the non-ecliptic bodies. The tidal forces slow down the orbItal periods but not the oscillations out of the ecliptic (what you called wobbles). – Lewis Miller Dec 18 '15 at 23:46
• Even if there's only one orbiting body The orbit will tend to go circular after a long time if there is enough tidal forces as with the large ocean. – Bill Alsept Dec 19 '15 at 0:21
• Also see Chaos in the Solar System: annualreviews.org/doi/abs/10.1146/… – Lewis Miller Dec 20 '15 at 22:23

Yes gravity effects this. As the planets orbit the sun they wobble above and below the plan slightly, some more than others. The solar system does the same thing as it orbits our galaxy. I suppose like a pendulum these wobbles are diminishing.