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Author Topic: Eaarth x 2?  (Read 6983 times)

Offline Roy P

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Eaarth x 2?
« on: 21/05/2006 11:46:07 »
If it were possible for two planets of the same size to gently come together, like a double Earth, say, what would the conditions on them be like -- specifically near the point of contact?

What would happen to the oceans?

Certainly, gravity would be stronger at the extremities of the two orbs, but would there be negative gravity surrounding the area close to the point of contact?

Interesting!

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Offline neilep

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Re: Eaarth x 2?
« Reply #1 on: 21/05/2006 13:38:55 »
Roy...WOO !!..that's got me pondering with fascination and wonder. Do you mean that the two planets would literally be touching but stable ?

Phew !!...could that even be possible ? to the degree where you could literally reach up and touch the edge of the twin planet...


I am looking forward to reading peoples postulations & hypotheses regarding this.

I wonder if at the point of contact the oceans would fill in the gaps effectively giving the appearance that the planets were indeed just one stretched body !...if you know what I mean.

I wonder if it would cause massive tectonic activity so that the core of each planet would be drawn towards the point of contact...hmmmm !
..I think it would be a gravity nightmare surely....but then...if the bodies are spinning as one around the point if contact wouldn't that bring centrifugal/centripetal effects into matter ?

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« Last Edit: 21/05/2006 13:43:50 by neilep »
 

Offline Roy P

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Re: Eaarth x 2?
« Reply #2 on: 21/05/2006 14:44:19 »
quote:
Originally posted by neilep

to the degree where you could literally reach up and touch the edge of the twin planet...

Yes. That was the idea, Neil.
quote:
I wonder if at the point of contact the oceans would fill in the gaps

Yup. That would probably be the scenario. But what if there were no oceans?
quote:
I wonder if it would cause massive tectonic activity so that the core of each planet would be drawn towards the point of contact

I don't see why? After all, at the crust -- the point of contact, gravity would only perhaps double?

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Offline neilep

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Re: Eaarth x 2?
« Reply #3 on: 21/05/2006 15:00:30 »
We need the experts to cast their specialist-knowledge-eyes on this one.



Come on experts...whajafink !! ?

Excellent post Roy...it's really got me wondering

Thanks

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« Last Edit: 21/05/2006 15:00:50 by neilep »
 

Offline DoctorBeaver

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Re: Eaarth x 2?
« Reply #4 on: 21/05/2006 22:54:36 »
1 issue that springs to mind is that where the spheres touch, the gravitational pull on that point from each sphere would be equal. That could be very interesting were it ocean on both planets where they touched. Could fish swim from 1 planet to the other?

Somehow, though, I'm not sure it would be possible. Bear in mind that gravity is an attractive force (arguably) between 2 objects. Therefore each planet would attract the other with equal force; meaning that the overall attraction between them would be doubled. Would that doubling be sufficient to wrench the crust of each planet apart on the sides where they touched? Imagine the earthquakes etc! (Yes, I know earthquakes aren't caused by gravity - but with twice the gravitational attraction, I think it's a distinct possibility.

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« Last Edit: 21/05/2006 22:55:27 by DoctorBeaver »
 

Offline Soul Surfer

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Re: Eaarth x 2?
« Reply #5 on: 21/05/2006 23:52:13 »
It is just not possible to bring two planets the size of the earth together gently.  Assuming that they could be placed in a position thet they ere in contact with each other if they were stationary or moving relatively slowly the gravitational forces and pressures would be enough for both globes to melt and coalesce to form a single spherical planet this would of course immediately boil off all the oceans and the whole thing would take some ime to cool down.

A more "gentle" process would be to have the two plannets orbiting each other around their common centre of gravity and gradually to reduce the size of the orbit but both planets would reach ther roche limits and disrupt each other well before they came into contact.  

The roche limit is the closest point that any orbiting body can get to another body. it occurs when the differential grvitational forces across the body exceed the mechanical strength of the body.

A good example of the amount of power that differential gravititional forces can have is jupiter's moon Io this is just about completely made up of hot molten rock because of the regular differential tidal actions of the other galilean satellites.  This effect was largely unsuspected until the voyager probes showed the unusual structure of that moon.

To continue as the two "earths" got closer together they would gradually distort away from spherical to become more pointed at the position of they were closest to each other  (let us assume that they stay in rotational mode lock with respect to each other. If they didn't tidal friction would rapidly cause this to happen and at the same time melt the planet) at the extreme condition they would be like a figure for infinity rotated round its long axis coming to a point at the point of contact. For two earths to do this the rotational period would be around a couple of hours.

At the surface of the double planet the gravitational field would always be perpendicular to the local surface (assumed to be smooth) but it would vary quite a bit over the surface being reasonably normal "around the edges" but would fall to almost nothing at the point of contact and be quite low at the opposite pole to the point of contact

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« Last Edit: 22/05/2006 00:12:02 by Soul Surfer »
 

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Re: Eaarth x 2?
« Reply #6 on: 22/05/2006 11:35:39 »
quote:
Originally posted by Roy P

If it were possible for two planets of the same size to gently come together, like a double Earth, say, what would the conditions on them be like -- specifically near the point of contact?

Roy P



Bear in mind that Earth is mostly liquid :-



" The earth is made of layers of rock and metal, some of which are molten.
The crust on which we live is a thin, brittle layer, like the shell of an egg.

The Earth is composed of three main layers of rock:

The crust is a relatively thin layer around the outside of the Earth. It is about six to seven kilometers thick under the oceans, and it ranges from 12 to 60 kilometers thick beneath the continents. Like the shell of an egg, the Earth’s crust is brittle and can break.
The mantle is about 2900 kilometers thick and is made mostly of melted rock.
The core is made of two layers: an outer core of melted rock and an inner core of solid rock.
Rock gets hotter the deeper it is underground.
As the rock of the mantle is melted, the colder, solid crust is actually floating on top of it."
http://www.seed.slb.com/en/scictr/watch/living_planet/beneath.htm
 

Offline tony6789

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Re: Eaarth x 2?
« Reply #7 on: 22/05/2006 14:17:39 »
ummm i don'tnderstand

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ROBERT

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Re: Eaarth x 2?
« Reply #8 on: 22/05/2006 14:41:18 »
quote:
Originally posted by tony6789

ummm i don'tnderstand

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Planet Earth is mostly liquid.
Two Earth like planets close together would coalesce like two drops of water.
 

Offline science_guy

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Re: Eaarth x 2?
« Reply #9 on: 22/05/2006 19:13:33 »
something that people aren't taking to account:  If two gravitational forces of even strength from two planets would not double the gravity in between the two "earths", what would happen, because they are on opposite sides, is they would cancel.

But assuming that they wont coalasce, what effect would the moon have?  would there be an identical moon for the other "earth"?  or would it remain just one and have an adverse effect on the tides?

E=MC2... m=deg/360 X C... C= PiD

therefore E=deg/360 X 2(PiD)
 

Offline neilep

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Re: Eaarth x 2?
« Reply #10 on: 22/05/2006 19:28:47 »
quote:
Originally posted by ROBERT

quote:
Originally posted by tony6789

ummm i don'tnderstand

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Planet Earth is mostly liquid.
Two Earth like planets close together would coalesce like two drops of water.



What about two planets that are mostly solid ?...or completely solid ?

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Offline Roy P

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Re: Eaarth x 2?
« Reply #11 on: 22/05/2006 21:34:01 »
quote:
Originally posted by science_guy

If two gravitational forces of even strength from two planets would not double the gravity in between the two "earths", what would happen, because they are on opposite sides, is they would cancel.

Yes. This is exactly what I assumed.

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Offline Roy P

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Re: Eaarth x 2?
« Reply #12 on: 22/05/2006 21:47:43 »
quote:
Originally posted by Roy P
Yes. This is exactly what I assumed.

Can I change that: Yes, it would be negative gravity for an independent body but, for the two 'Earths' it would be 2G -- wouldn't it?

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Offline science_guy

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Re: Eaarth x 2?
« Reply #13 on: 24/05/2006 08:48:38 »
2G is assuming that they pull the same direction.  line up the earths so that the front earth eclipses the back earth, and you would have increased gravity.  but in between, the gravity is pulling in opposite directions, on earth one it would provide itself with 1G, and earth two would provide -1G.  The same goes for earth two.  Gravity always acts from the center of the mass.

E=MC2... m=deg/360 X C... C= PiD

therefore E=deg/360 X 2(PiD)
 

Offline Soul Surfer

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Re: Eaarth x 2?
« Reply #14 on: 24/05/2006 10:26:16 »
Although the net gravitational field at the point of contact would be small because of the equal and opposite effects of the two "earths"  the pressure at the point of contact would be absolutely enormous because ot the weight of the total planets pressing on a small point of contact this would just push ANY solid material around like plasticine and generate vast quantitieas of energy as the two globes coalesce.


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Offline DoctorBeaver

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Re: Eaarth x 2?
« Reply #15 on: 24/05/2006 12:04:45 »
I think maybe I didn't properly explain what I meant so let me try again:-

Gravity acts as if from the centre of mass, yes - but it is a 2-way process with each mass attrating the other. I was basically saying what SoulSurfer said, but he explained much more eloquently than I.

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Offline Roy P

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Re: Eaarth x 2?
« Reply #16 on: 24/05/2006 17:33:19 »
Dammit. You scientists just have to ruin everything don't you :) I hadn't considered the 'weight' thing -- even though it was so obvious. I couldn't see beyond the 'negative' gravity aspect!

OK. What if the two earths had a crust thick enough not to break like an eggshell, and only coalesced a little bit? It would be fun near the contact area wouldn't it!

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Offline science_guy

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Re: Eaarth x 2?
« Reply #17 on: 25/05/2006 19:08:45 »
quote:
Dammit. You scientists just have to ruin everything don't you :)
I'm not a scientist, im a freshman in high school ;)

quote:
OK. What if the two earths had a crust thick enough not to break like an eggshell, and only coalesced a little bit? It would be fun near the contact area wouldn't it!

Yes, it may be fun at the contact area, but the combined forces of gravity may be unstable enough to pull you apart.  Although the two forces cancel eachother, they are still acting on your body.

E=MC2... m=deg/360 X C... C= PiD

therefore E=deg/360 X 2(PiD)
 

Offline DoctorBeaver

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Re: Eaarth x 2?
« Reply #18 on: 25/05/2006 23:47:59 »
Another interesting point, surely, is that if the point of contact were to crumble, that would mean the centres of the 2 planets would become correspondingly closer hence further increasing the gravitational attraction between them.

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Offline Atomic-S

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Re: Eaarth x 2?
« Reply #19 on: 31/05/2006 05:12:55 »
quote:
Yes, it may be fun at the contact area, but the combined forces of gravity may be unstable enough to pull you apart. Although the two forces cancel eachother, they are still acting on your body.
Actually, no. Your body would be pulled apart only by differential gravity, not by absolute gravity. The gravitational force between two very-nearly touching spheres, in the region of closest proximity, is, as noted above, cancelled. The differential of it, however, is doubled (the potential curves add); however the amouunt of gravitational gradient at the earth's surface is tiny, and even doubling it would not place any significant stress on the human body. A person located in  such a region would experience a slight attraction to whichever of the 2 planets he was standing on, and would require a small amount of speed to jump from one to the other, across the very small potential hill between them. This of course assumes that the planets are not rotating with respect to each other, and are held in fixed positions by some external means.
« Last Edit: 31/05/2006 05:17:13 by Atomic-S »
 

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Re: Eaarth x 2?
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