Hi Pop Worlds

[Oaty_bars]

Um, there's nothing easy about moving planets. I'd argue that if you had the unobtainium materials then it'd probably be easier to create a ringworld.

I don't think there would be enough material in one system to create a ringworld....

Planets are bloody massive, and the only thing that will move one is a similar mass. If you can make a black hole and use it as a "tug" to move the planet to a new orbit then great, but I'd suspect that the black hole would cause problems for the planet in the process .

Some Planets (like Earth) are like an egg, hard shell, softish center,
you would need to move it very slowly or risk breaking it apart,

Gravity would be the best option (so far) to move such a thing,
but you would need to leave the world first, the tectonic action on a shifting world would equal massive earthquakes and tsunamis

 

[EDG]

Assuming we can trust Niven and others*, the easiest way would is to move a Gas Giant** into a capture position relative to the planet, then move the GG to where you want the planet.

That's even worse. gas giants are 1000-10000 times more massive than an earthlike planet. If you can't move an earthlike planet easily for reasons I already stated, you certainly can't move a gas giant.

 

[EDG]

Some Planets (like Earth) are like an egg, hard shell, softish center, you would need to move it very slowly or risk breaking it apart,

Like a hard-boiled egg made of rock maybe . The mantle's not much less "hard" than the crust, only the outer core is liquid. There's enough rigidity there for it to withstand orbital velocity and acceleration - so long as its moved at those sorts of accelerations there shouldn't be any risk of it breaking apart.

 

[Gaidheal]

Not to mention that if you did move such a massive planet as a 'gas giant' the knock-on effect on the rest of the solar system would be significant, especially the inner solar system, which is the bit we most care about...

 

[GypsyComet]

I rather like Kemplerer Rosettes, but that may be due to having read "Flight of the Dragonfly".

 

[Oaty_bars]

Some Planets (like Earth) are like an egg, hard shell, softish center, you would need to move it very slowly or risk breaking it apart,

Like a hard-boiled egg made of rock maybe . The mantle's not much less "hard" than the crust, only the outer core is liquid. There's enough rigidity there for it to withstand orbital velocity and acceleration - so long as its moved at those sorts of accelerations there shouldn't be any risk of it breaking apart.

Dude, Earth is in a settled orbit, with most of the kinks in the tectonics ironed out after billions of years orbiting the sun, it has now mostly settled (yet the shift in surface weight due to seasonal changes is still enough to cause a tectonic shift) the crust is not as strong as you think, and the core will continue to want to move sepearately from the crust if you tried to move just the planets surface,

"withstand orbital velocity and acceleration" is a silly statement,
of course it can, in the same way you can walk across a moving train,
that has nothing to do with strength, its all moving at the same speed,

Bit if you just redirected a tiny fraction of that orbital speed in to another direction it would be more than enough to rip this world apart,

So, no you would need to move very slowly indeed

 

[Gaidheal]

Actually, probably not... as observed, there is indeed a molten core but the vast majority of our planet is what most people would consider 'solid' and its also very massive (albeit dwarfed by some other planets, our star, etc) and will very much tend to stay together - in fact, that is why it is a planet at all.

 

[EDG]

"withstand orbital velocity and acceleration" is a silly statement, of course it can, in the same way you can walk across a moving train, that has nothing to do with strength, its all moving at the same speed,

It really isn't. All orbits are elliptical. Planets travel faster when they are closer to the star and slower when they are further - therefore there is some orbital acceleration and deceleration.

 

[captainjack23]

Assuming we can trust Niven and others*, the easiest way would is to move a Gas Giant** into a capture position relative to the planet, then move the GG to where you want the planet.

That's even worse. gas giants are 1000-10000 times more massive than an earthlike planet. If you can't move an earthlike planet easily for reasons I already stated, you certainly can't move a gas giant.

Except.......

when you can use the Gas giant as fuel, and start from the idea that whatever happens to the GG is irrelevent. The fact that they are big (which of course I already knew ..... ) is used to advantage.


Sorry, I was assuming that you were familiar with the whole idea from "A world out of time" (which I am aware, I hasten to add, before we mistake each other , is fiction).


here's a quick summary of it; (I cant recall from where -its in my traveller trivia folder...)

Building a gas-giant colony ship is not as difficult as it looks.
Build a fusion candle. It's called a "candle" because you're going to burn it at both ends. The center section houses a set of intakes that slurp up gas giant atmosphere and funnel it to the fusion reactors at each end.
Shove one end deep down inside the gas giant, and light it up. It keeps the candle aloft, hovering on a pillar of flame.
Light up the other end, which now spits thrusting fire to the sky.
Steer with small lateral thrusters that move the candle from one place to another on the gas giant. Steer very carefully, and signal your turns well in advance. This is a big vehicle.
Balance your thrusting ends with exactness. You don't want to crash your candle into the core of the giant, or send it careening off into a burningly elliptical orbit.
When the giant leaves your system, it will take its moons with it. This is gravity working for you. Put your colonists on the moons.
For safety's sake, the moons should orbit perpendicular to the direction of travel. Otherwise your candle burns them up. They should also rotate in the same plane, with one pole always illuminated by your candle (think "portable sunlight"), and the other pole absorbing the impact of whatever interstellar debris you should hit (think "don't build houses on this side")
Whether or not your gas giant heats up to the point that it ignites and turns into a small star depends largely on how much acceleration you're trying to get out of your candle. Remember, slow and steady wins the race!

Addendum to Note: Larry Niven suggested that such an arrangement could be used to move rocky worlds from one orbit to another, and he wrote a novel entitled A World Out of Time in which the Earth was moved with the help of giant candle they'd shoved up Uranus. I'm not making this up.

Theres also an interesting if somewhat tangential discussion of the mechanics of such a fusion candle here:

http://newsgroups.derkeiler.com/Archive/Rec/rec.arts.sf.composition/2006-05/msg02097.html

 

[Oaty_bars]

"withstand orbital velocity and acceleration" is a silly statement, of course it can, in the same way you can walk across a moving train, that has nothing to do with strength, its all moving at the same speed,

It really isn't. All orbits are elliptical. Planets travel faster when they are closer to the star and slower when they are further - therefore there is some orbital acceleration and deceleration.

Yes, I know that, but as everything is in acceleration and deceleration at the same time it not likely to rip the planet apart now is it

 

[Oaty_bars]

Actually, probably not... as observed, there is indeed a molten core but the vast majority of our planet is what most people would consider 'solid' and its also very massive (albeit dwarfed by some other planets, our star, etc) and will very much tend to stay together - in fact, that is why it is a planet at all.

Its the dense core that really keeps this world on track, but the surface is brittle, and not a single solid shell, but is made up of floating broken chunks of that shell, its fluid, and inside not really that solid at all,

and the reason this is a planet is gravity,

 

[Gaidheal]

I am familiar with the 'fusion candle' idea, by the way, I still hasten to point out the impact on the rest of the solar system. :¬)

 

[Gaidheal]

Gravity == mass, Oaty, along with inertia ;¬)

The planet is a planet and not an asteroid belt because of the proximity and total mass. This same fact is what means it will tend to stay together under even quite 'large' accelerations (by most standards).

By the way, gravity from Earth is pretty modest at only about 10 m/s/s at Sea Level.

 

[captainjack23]

I am familiar with the 'fusion candle' idea, by the way,

I was just surprised that EDG didn't seem to be. Or that I initially described too sketchily.

I still hasten to point out the impact on the rest of the solar system. :¬)

The idea does seem to assume that you don't give a flip about that, I suspect.....

 

[EDG]

Yes, I know that, but as everything is in acceleration and deceleration at the same time it not likely to rip the planet apart now is it

Neither will moving it any other way. The whole planet will still be accelerating at the same rate, just in a different direction - so why should that rip itself apart? Planets really aren't as fragile as you think they are.

 

[Oaty_bars]

Gravity == mass, Oaty, along with inertia ;¬)

The planet is a planet and not an asteroid belt because of the proximity and total mass. This same fact is what means it will tend to stay together under even quite 'large' accelerations (by most standards).

By the way, gravity from Earth is pretty modest at only about 10 m/s/s at Sea Level.

Dude, yes Mass = Gravity (didn't we already cover this)
but Mass does not = inertia, but Mass = inertia resistance,

The planet is a planet due to Gravity pulling in more and more Mass,

 

[EDG]

when you can use the Gas giant as fuel, and start from the idea that whatever happens to the GG is irrelevent. The fact that they are big (which of course I already knew ..... ) is used to advantage.

Can't really see how. Having read your summary (and the responses in the link that say it's pretty much impossible to get any decent acceleration to affect the GG's motion in a non-geological timescale), it's not going to work anyway.

 

[EDG]

Dude, yes Mass = Gravity (didn't we already cover this)
but Mass does not = inertia, but Mass = inertia resistance,

Gravity is a side-effect of Mass. Inertia is a property that all masses have (for reasons unknown). The bigger the mass (in magntitude), the greater the inertia. Gravity depends on distance from the mass though.

The planet is a planet due to Gravity pulling in more and more Mass,

A planet is a planet because it's a large solid or gaseous body that isn't big enough to ignite as a star. None of which has any particular relevance to whether or not it can survive being moved from one orbit to another.

 

[EDG]

I was just surprised that EDG didn't seem to be.

It helps if you don't assume that your readers know things that you know.
I'm not actually that familiar with Niven - all I've read is Ringworld and its first sequel. And some of his short stories (in Inconstant Moon).

 

[Oaty_bars]

Dude, yes Mass = Gravity (didn't we already cover this)
but Mass does not = inertia, but Mass = inertia resistance,

Gravity is a side-effect of Mass. Inertia is a property that all masses have (for reasons unknown). The bigger the mass (in magntitude), the greater the inertia. Gravity depends on distance from the mass though. .

Gravity is created by Mass,
And yes Gravity depends on distance from the mass,

But a Mass is resistant to Inertia, The bigger the mass the greater the resistance

The planet is a planet due to Gravity pulling in more and more Mass,

A planet is a planet because it's a large solid or gaseous body that isn't big enough to ignite as a star. None of which has any particular relevance to whether or not it can survive being moved from one orbit to another.

Thats not true at all, a planet is born from a build up in Mass,
Mass = Garvity, hence drawing more Mass, which creates more gravity,
rinse and repeat until, bingo, one planet sized body,

If a body does not have enough mass, then it does not have enough gravity to ignite as a star,

Stars are born the same way, but just get to harvest more mass at birth,