Why does Lunar orbit are unstable

[Pawelk198604]

I heard that orbit around the Moor are very unstable with exception of some orbital inclinations. I wonder why is this? 

[Canopus]

The moons mass isn't evenly spread around. It has Pockets of denser materials all over its surface. 

https://en.wikipedia.org/wiki/Mass_concentration_(astronomy)

[Bill Phil]

Mascons. Mass - con. Mass concentration. Basically, what @Canopus said. The Earth technically has the same thing, but it's much more differentiated and as such the majority of the mass is concentrated in the center and spread out pretty well. Essentially, Earth's are a little bit less concentrated. For example, in the article linked above, the region around Hawaii is mentioned to have a mascon.

[Helmetman]

Not to qualified to say much anything about this. Ignore, hit, sue, debunk, scold demonize me if I'm wrong.

But Earth has a lot more internal geological processes then the moon. The earth is constantly reshaping itself in it's interior while the moon does so much less (next to nothing in comparison)

I'm not sure how/if this affects orbits and in which manner. I'm also not sure how this information is even usefull concerning our current satellite network and/or other things that may be affected by it.
But as the users said above, this is true for moon and Earth, and consequently any planet out there with varying differences.

Edited September 30, 2017 by Helmetman

[magnemoe]

38 minutes ago, Helmetman said:

Not to qualified to say much anything about this. Ignore, hit, sue, debunk, scold demonize me if I'm wrong.

But Earth has a lot more internal geological processes then the moon. The earth is constantly reshaping itself in it's interior while the moon does so much less (next to nothing in comparison)

I'm not sure how/if this affects orbits and in which manner. I'm also not sure how this information is even usefull concerning our current satellite network and/or other things that may be affected by it.
But as the users said above, this is true for moon and Earth, and consequently any planet out there with varying differences.

Moon don't have an large core it also stopped being geological active pretty soon as its small, then hit it with lots of metallic asteroids who generate mass concentrations on the surface. 
In a few places local gravity gradient would be noticeable even with an line and weight.

And this distort low orbits, not much an issue for higher orbits however but you want to go low for most science satellites, Higher orbits get distorted by earth however. 

[Pawelk198604]

3 hours ago, magnemoe said:

Moon don't have an large core it also stopped being geological active pretty soon as its small, then hit it with lots of metallic asteroids who generate mass concentrations on the surface. 
In a few places local gravity gradient would be noticeable even with an line and weight.

And this distort low orbits, not much an issue for higher orbits however but you want to go low for most science satellites, Higher orbits get distorted by earth however. 

distorted by earth?

[kerbiloid]

Moon's Hill sphere and Sphere of influence are 60..66 thousand km = 35..38 Moon radii.
So, when a satellite gets enough high from the mascons, it gets very close to the outer limits.

[Scotius]

Moon is a veritable bonanza It's much smaller than Earth. It's not geologically active as much as Earth and less differentiated. Which means all heavier elements are closer to the surface - we don't have to dig as deep to reach the good stuff. It's also pockmarked with remains of asteroids, which brought even more metals. On Earth they sank towards the core - on the Moon they are at more manageable depths. Sure, it might be cheaper to bring materials from NEO's and asteroid belt - but short distance to the Moon has its own advantages.

[kerbiloid]

55 minutes ago, Scotius said:

Which means all heavier elements are closer to the surface

... of the Earth. Because the proto-Moon metal core has been swallowed by the Earth.
While the Moon is originally just a piece of the proto-Moon crust with remains of the core sticked below.

Though, actinides (incl. U) probably should be still in the Moon, as they are lithophile elements.
But unlikely their distribution depends on their atomic mass or density due to their low concentration.
And exactly they haven't been washed up by hydrothermally like on the Earth.

Very likely the lunar seas (which are the biggest mascons) are craters not made by asteroids, but by original Earth satellites or by other remains of the proto-Moon crust.

Edited October 1, 2017 by kerbiloid

[Green Baron]

1 hour ago, kerbiloid said:

... of the Earth. Because the proto-Moon metal core has been swallowed by the Earth.

Do you mean Theia by proto-moon ? It is not quite clear how much Theia and earth had already differentiated, but they probably had to a high degree. The moon's density is lower then the earth's because it's mostly formed of mantle material of the already differentiated bodies.

1 hour ago, kerbiloid said:

Very likely the lunar seas (which are the biggest mascons) are craters not made by asteroids, but by original Earth satellites or by other remains of the proto-Moon crust.

While there are craters on the moon that have filled with basalt, the maria on moon themselves are no craters, but solidified outflow of basalts. They are volcanic rather than impact structures. They are older than the lighter surface structures from impacts that formed after the outflows and solidification of the crust.

[kerbiloid]

27 minutes ago, Green Baron said:

Do you mean Theia by proto-moon ?

Theia is a _commercial name for the proto-Moon in the impact theory.
It is currently prevalent theory, but not the only one, and Theia is not an official name for that presumed celestial body.

27 minutes ago, Green Baron said:

It is not quite clear how much Theia and earth had already differentiated, but they probably had to a high degree. The moon's density is lower then the earth's because it's mostly formed of mantle material of the already differentiated bodies.

Yes, and as in impact therory, so in tidal theory, most part of the core has gotten down into the Earth, the Moon gets only silicate crust and a small part of the iron core.

27 minutes ago, Green Baron said:

the maria on moon themselves are no craters, but solidified outflow of basalts. They are volcanic rather than impact structures.

If somebody can distinguish volcanic and impact events in the first million of the hot and partially melted Moon existence, when its orbit supposedly was growing from several thousand km (Roche limit, several hours period) up to 1/3-1/2 f of her current orbit.
In case of impact: all pieces of the proto-Moon/Theia thrown into orbit, anyway should fall either onto the Earth, or onto the Moon, and not immediately.

Upd.
In any theory the Moon's gravitational differentiation should mostly happen before the crash, otherwise it shouldn't loss the core already separated from the crust. With most part of volcanism.
The only differnce: the impact theory presumes that Theia had been differentiated on its own gravity before being captured/intercepted by the Earth,
while the tidal theory presumes that the lightweight and non-differentiated proto-Moon had been melted by tidal forces in LEO and its gravitational differentiation was rapid, forced and dramatic.
And every lunar sea has a pancake of dense rocks below, as if they were impact places.

Edited October 1, 2017 by kerbiloid

[Green Baron]

23 minutes ago, kerbiloid said:

If somebody can distinguish volcanic and impact events in t

Yes, "somebody" actually can.