Will our planet always stay in orbit?

[GrandMasterK]

I know the earth absorbs matter from the universe and I imagine some matter escapes. I'm gonna guess and say the earth is gathering more than it lets go. Would raises a question of mine. A certain number of things have to stay generally the same for something to stay in orbit right? Like size, speed and distance from the object it's orbiting. The sun is pulling the earth in as the earth is trying to get away at just the right amount to keep earth in orbit. My question is how much can the earth gain or lose before the orbit is dangerously interrupted. I read or heard somewhere (maybe it was this forum) that if we ever mined on the moon that we would have to be careful how much we take off it or else it could crash into the earth.

[thedarkshade]

I know the earth absorbs matter from the universe and I imagine some matter escapes.

There is something called "Conservation of Matter" which states that the amount of matter is always constant. Nothing can escape from earth (except space rockets) because nothing has natural velocity able to escape earth's gravitational field.

[Mr Skeptic]

There is something called "Conservation of Matter" which states that the amount of matter is always constant. Nothing can escape from earth (except space rockets) because nothing has natural velocity able to escape earth's gravitational field.

 

A large asteroid can blast earth rocks into space as well. That's a rather small effect, though, unless the asteroid were large enough to shatter earth.

 

The lightest atoms (eg hydrogen) can be blown out of the atmosphere by the solar wind, which is why light planets don't have much hydrogen compounds such as water.

[insane_alien]

There is something called "Conservation of Matter" which states that the amount of matter is always constant.

 

in a closed system. the earth can generally be regarded as closed but to be accurate, it's not. there a few thousand tonnes of impacting material every month.

 

Nothing can escape from earth (except space rockets) because nothing has natural velocity able to escape earth's gravitational field.

 

not true, hydrogen, helium and many other light gaseous molecules have enough velocity from thermal motion to escape. not to mention ejecta from more major asteroid impacts.

 

as for the origional question, the mass leaving the earth/moon can be neglected, it is the stuff your landing that you need to worry about.

 

though, as long as the direction of impact is random the impulse imparted should average out to zero or some very small number. most likely the angular momentum of the impactor will be in the same direction as earths. this means it won't change the orbital velocity at all.

 

either way, the sun will expand to engulf the earth long before that would have an effect even in the worst case scenario.

[thedarkshade]

The lightest atoms (eg hydrogen) can be blown out of the atmosphere by the solar wind, which is why light planets don't have much hydrogen compounds such as water.

I think that's because they're on the outer layers of atmosphere (because of their weight), like tritium.

[insane_alien]

yes but they can start off at the surface and still escape. things generally don't leave from the middle anyway. thats like popping out of existance from the middle of a room instead of walking to the door and going through it.

[qwe)k]

either way, the sun will expand to engulf the earth long before that would have an effect even in the worst case scenario.

 

I swear there is a theory that exists that says the earth just shoots off into space. This would be because of the sun collapsing and therefore having a much smaller effect on the earth. This seems logical on a simplistic level.

 

Or would the suns expansion be to fast?

 

Please tell me if i'm wrong.

[Klaynos]

The sun's size is relatively unimportant, as long as it's mass is constant.

 

The earths orbit is a slight spiral towards the earth IIRC... Also I think the mass of the earth is independent of it's orbiting perameters, I'm pretty sure that the mass of the orbiting body is removed from the equation....

[JaKiri]

in a closed system.

 

In a classical closed system. SR invalidates mass conservation.

[uncool]

The sun's size is relatively unimportant, as long as it's mass is constant.

 

The earths orbit is a slight spiral towards the earth IIRC... Also I think the mass of the earth is independent of it's orbiting perameters, I'm pretty sure that the mass of the orbiting body is removed from the equation....

 

True, as the only force that changes the direction of the Earth is a mass-independent force - gravity.

=Uncool-

[Mr Skeptic]

I believe that the current understanding is that the earth will be blown by the solar wind just enough to be out of the way when the sun goes red giant (the earth will get toasted but not fall into the sun). If we're still around by then, we may have moved the earth ourselves, eg by using the slingshot effect to slowly accelerate the earth using asteroids.

[ajb]

This is the n-body problem and it's stability. This is an old question in classical mechanics.

 

The n-body problem is in general non-integrable and may be chaotic!