# Thread: Effect of a planet on the earth. (Not PX!)

1. g99
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## Effect of a planet on the earth. (Not PX!)

What would be the effect on earth is a second Earth sized mass appeared within the moons orbit.

O.K. lets propose a example. Say 500 years in the future space travel is common and artificial gravity generators can happen. One of these ships with a artifical gravity generator is in orbit and switches on its generator causing the gravity well surrounding the ship equal to a planet the size of the earth. Normally this is negated by genrerators on the hull of the ship. Thse second generators negate the effect beyond the hull of the ship. But for some reason it fails this time.

So what would the effect be on the earth if suddenly the gravity well of another earth apeared next to it?

I imagine extreme tides like we have never seen before and a rush of loose mass (air, water, us) towards the ceneter of mass. right?

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Well, the Earth is roughly 80 times as massive as the moon. Assuming these distances are close to the earth moon distance, I'd expect tidal variations 80 times greater than what we currently have. That'd be pretty extreme. Of course you said size of the earth, so if you're talking volume you'd also need to provide a density, I assumed you meant mass.

As far a gravitational effects on the surface, I get a change in acceleration of only .002 so it looks like 9.81 m/s^2 would still apply. Doesn't look like much being sucked away, certainly not off the planet all together.

As far as what would happen to the orbit. That would depend a lot on what this other mass was doing before it became 'visible'. If it's not in an orbit that would be stable for two objects of that size, the the moon thrown in the mix as well, and I'm not sure there would be a stable orbit that close, it's going to get real ugly for people on both planets. Solar eclipses might be cool, but you probably wouldn't get too many annular eclipses.

Rich

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## Re: Effect of a planet on the earth. (Not PX!)

Originally Posted by g99
What would be the effect on earth is a second Earth sized mass appeared within the moons orbit.

O.K. lets propose a example. Say 500 years in the future space travel is common and artificial gravity generators can happen. One of these ships with a artifical gravity generator is in orbit and switches on its generator causing the gravity well surrounding the ship equal to a planet the size of the earth. Normally this is negated by genrerators on the hull of the ship. Thse second generators negate the effect beyond the hull of the ship. But for some reason it fails this time.

So what would the effect be on the earth if suddenly the gravity well of another earth apeared next to it?

I imagine extreme tides like we have never seen before and a rush of loose mass (air, water, us) towards the ceneter of mass. right?
I'm not too keen on your scenario. A spaceship wouldn't need to have a gravitational field as intense as Earth's in order to have a 1 g field--that is, not unless the space ship is as big as the earth.

However, if you assume someone put warp engines on Venus, or a spindizzy drive on Deneb VII and flew it to earth, you might get the situation you're describing.

You'd get huge tides. Assuming the planet appeared where the moon is now, you'd get a tidal force 80 times the size of that induced by the moon. If it were only half as far as the moon, the tides would increase by another factor of 8--640 times the tidal force from the moon.

That's not to say that tides would be 1000 feet high where before they were only a foot high--the height of the tide is influenced to a great extend by the shape of the basin. Damp driven oscillations, and all that. Coastal areas aren't going to be very congenial, though.

There's not going to be a tremendous force pulling all the loose stuf to the center of mass--the gravity would presumably be acting on everything simultaneously (let's skip for the moment what simultaneous means in this context)--everything is going to be pulled at the same time although not quite by the same amount (tidal force).

I expect that there would be some nasty quakes as a result.

4. g99
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thanks! :-) very interesting.

How would the moon be effected?

Remind me to discontinure to warp drive order for venus. :-)

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Well, again it depends on where it materializes. If it shows up at L4 or L5, its influence on the moon will be precisely the same as the earth's (it weighs the same as the earth, and is as far away as the earth). I'm not sure that this is a stable configuration--the moon is going to assume a different orbit. When the intruder leaves, the moon is going to be in a lot more elliptical orbit.

Again, if it plopped down halfway between the earth and the moon, the tidal force it exterted on the moon would be eight times greater than the tidal force of the earth. This is going to change some of the stresses; it might cause some moonquakes. I don't know about this, though. If the moon is seismically dead perhaps not too much would happen.

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