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Moon's Moon


Swexic
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Can there exist a planet... with a moon... with a moon?

In theory a moon could hold it's own moon within it's gravity

W1sYE.png

You figure that if there is a sun, and it's gravity allows planets to hold moons, a planet (Acting as a sun) would would be able to have a moon (Acting as a planet) with it's own satellite (Acting as the Moon). Of course I could be incorrect as I only have about a Full 8th Grade education of Astronomy and Mathematics with bits and pieces of 9th grade. Please do correct me if I am wrong in my thinking.

Edited by Swexic
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The acceleration due to gravity acted upon this "Moon - Moon" leads to it accelerating towards the larger planet on one side and decelerating as it passed around the other side of the first moon, over time the apoapsis will grow and the periapsis will shrink, with either the "Moon - Moon" reaching escape velocity and flinging off into space or plummeting into the Moon. For example, the Lunar module left over in Lunar orbit after returning from the surface in the Apollo 11 mission crashed into the Lunar surface several months or maybe even a few years after it was discarded by Neil Armstrong and Buzz Aldrin.

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For example, the Lunar module left over in Lunar orbit after returning from the surface in the Apollo 11 mission crashed into the Lunar surface several months or maybe even a few years after it was discarded by Neil Armstrong and Buzz Aldrin.

Actually, that has more to do with the Moon's lumpy gravity field, but yes, you are correct as to why a moon-moon would destabilize over time.

Although, a planet with, say, Neptune's mass orbiting at 1000 AU, with a moon with Mars' mass orbiting a few million km away COULD potentially house a satellite of its own, but it's ridiculously unlikely.

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Once I drew a diagram called the "Ultimate Axis Under Two", which showed this:

A spacecraft orbiting the moon of a moon, which is in a binary orbit with a second moon, which itself has another moon and spacecraft orbiting that second moon. Then, the two moons were orbiting a planet, which was orbiting around a dual star system. The stars are orbiting around the centre of the galaxy, and those around a cluster, and that around a supercluster, and around a black hole, which is going around the universe.

Therefore, the original spacecraft is orbiting around 10 different axes, including its own centre of gravity.

My science is probably at least slightly wrong, what with a cluster going around a supercluster and whatnot, but I don't care about the physics.

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Best case scenario for a Moon Moon Moon, Large star, large distant gas giant, large distant moon, close asteroid, closer meteorite. There are asteroids with very stable satellites going around them (A satellite is anything orbit gravitationally to something else.) Perhaps even some dust could orbit that meteorite... But everything is orbiting a lot more stuff. Going from the moon, the moon orbits the Earth orbits the sun orbits a supermassive black hole orbits the virgo cluster of galaxy orbits some large mesh of stuff at the center of the universe probably orbits a cluster of universes possibly orbits another multiverse, everything is moving really fast. You cannot measure absolute velocity, acceleration, or location, only relative. Perhaps the entire everything is moving at the speed of light constantly... And also every galaxy is moving outward, adding more speed. Such large things make me feel small, and maybe there are multiple everythings, each one being one single quark of a proton/neutron in an atom, in a molecule, in a thing, on a planet, going around a star... All made of quarks that are made of everythings... Lecture over!

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A satellite is anything orbit gravitationally to something else.

Careful. Anything in an elliptical orbit. If it's on a hyperbolic (i.e., escape trajectory) orbit, then it's not a satellite, it's technically an independent body...

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I've always wondered if someone...probably really bored...sat down and tried to compute the vector of a person idle (they don't have to be idle, but that's one less vector to put into the equation) on a given point on the surface of the Earth at a particular given time.

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In relation to what do you want that vector to be? It'd be zero to the Earth, and from there you take the surface rotation vector and add the Earth's, the Sun's and whatever it is the Sun orbits orbital vectors, until you arrive at whatever origin.

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  • 6 months later...
I think its possible to have a asteriod orbiting a moon, and for that asteriod to have a small moon itself.

The problem is tides as explained, stuff left in Moon orbit will stay for some years and then either fall down or end up in earth orbit.

In KSP this is not an problem as the game don't use tidal forces.

You can also put an satellite in orbit around the moon, however an sub moon has to stay in orbit for millions of years or we would probably not see it.

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