Earth Goes Poof, Wherefore Art Thou Luna?

[RexMundi]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

The sudden disappearance of Earth gravitational pull would would probably I think put the moon into an elliptical orbit going out past Mars and in closer than Venus.

 

Why?

 

~Rex

[Ian Mackinder]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

Why?

 

~Rex

 

I'm not sure (rarefied territory for me) but he might be thinking of stuff to do with transfer of momentum.

 

The following thought experiment grossly over-simplifies a complex problem, but consider.

 

Imagine tying a weight to a length of string and whirling it around. Once the twirling is up to a certain speed, things are nice and stable. The more weight at the end, the slower this speed has to be - you expend more effort to get it going but, once it is, again nice and stable.

 

So what happens if the string is suddenly shortened? The "Orbit" becomes smaller and the weight whips around faster - same energy, just less distance. So, what happens if the string remains the same length, but a very big part of the weight suddenly vanishes? Whatever is released will zoom off somewhere, and the portion still attached?

 

Add to that picture, suppose the string is elastic, and only partially stretched. When all that weight at the end vanishes, I imagine that the elastic will probably try to "pull in" whatever is left.

 

The dynamics of the Sol-Earth-Moon system are a heckuva lot more complex than this simplistic premise, but I hope the idea is helpful.

[Clonus]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

Why?

 

~Rex

 

Because it's almost certainly going to be moving at an angle to Earths orbit at the moment of disappearance. There's no way it will actually escape the suns gravity but that's going to give it a significant impetus making for a less regular orbit. Of course I'm not sure how irregular the result could be. but it will be more irregular than the current earth/moon system orbit.

[Ian Mackinder]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

That too.

[RexMundi]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

Because it's almost certainly going to be moving at an angle to Earths orbit at the moment of disappearance. There's no way it will actually escape the suns gravity but that's going to give it a significant impetus making for a less regular orbit. Of course I'm not sure how irregular the result could be. but it will be more irregular than the current earth/moon system orbit.

 

I was looking at some of the trajectory paths on various sites....just going with the layman definitions losing the earth shouldn't be more then a speed bump in the course of the moons orbit around the sun. I mean, the Sun has roughly twice the gravitational effect on the moon as Earth does, and the orbital path is more like this convex looking spiral thing then a sphere going round and round another sphere so it's not like snipping off an anchor weight on a physical model and the smaller sphere goes whipping off in some random direction. it would still need to overcome the force of the Sun's pull in order to really go anywhere, and without the earth to Rob energy from on a regular basis, it seems like it would actually steady out in orbit rather then get more eccentric.

 

~Rex

[Cancer]

Re: Earth Goes Poof, Wherefore Art Thou Luna?

 

Yeah, the Moon's orbital velocity around Earth is about 1 km/sec. The Earth/Moon system's orbital velocity around the Sun is about 30 km/sec. So if you cut the Moon free, at most it's got about 3% extra kinetic energy to make for an orbital difference. Depending on the details of how it's cut loose, the orbital eccentricity (and inclination) will be changed some, but changing it so it crosses Venus's orbit ... there's not enough oompf there.