View Full Version : Destruction of a world

28-11-2007, 10:22
Right in all sci fi stuff there is talk of destroying worlds etc.
My point is that once said world has been destroyed, broken apart etc, would that not destory the entire solar system.
As my understanding goes a star wobbles with a planetary system orbiting it so with the destruction of one of the planets would that not have a catacylismic effect on the stars gravity pull causing the other planets orbits to be massively disturbed and in effect destroying them aswell.
If this is true it would be easier for an attacker to destroy another world in the system i.e. a less heavilly defended world as its destruction would surely destroy the intended world, or would this not work.

28-11-2007, 10:25
I wouldn't imagine the effect on the star would be that noticable. For one thing, presumably much of the planet's mass would still be orbiting the star (in the form of broken bits of planet).

I could of course be wrong. I don't intend to test my theory to try and prove it :)

28-11-2007, 10:34
Im with Bombot on this one, the mass is still there.

In addition to this a star is MASSIVE so the destuction of one small object would maybe change its nature very very slightly but not enough to tear a solar system appart.

Also remember that gravity would smush a planets remains back together most of the time and that Sci Fi always exagerate planets blowing up for dramatic effect.

28-11-2007, 10:59
It doesn't take a lot to make a star go nuts - it is after all a ball of gas. If you were to instantaneously erase a planet's mass from space, the gravitational ripples might well cause a noticeable change in activity on the sun for a short time. Stars tend to flare when they're disturbed, so you'd probably see a change in flare activity. The other planets would likewise be affected, as gravitational perturbations are most definitely significant in determining orbits.

28-11-2007, 11:14
Flares and whatnot I could believe. That's a long way from some kind of chain-destruction of the solar system of course.

28-11-2007, 12:26
I still wonder about the physics of the original thought, I mean, just because you remove something from the area doesn't mean that the gravity the star excerted on said object emmediately gets distributed to everything else arround the star does it?

28-11-2007, 12:30
Well i know for a fact that gas giants make a star wobble greatly so if it were destroyed then the star would not wobble to the same magnitude, that would have to have some sort of major effect.

28-11-2007, 12:32
Wolf, remember that destroying an object and eliminating its mass are not the same thing.

de Selby
28-11-2007, 13:03
The influence of (say) Earth's gravity on the dynamics of the rest of the solar system is very small. Plus, when you 'destroy' a planet you don't actually remove any of its mass-energy from the universe, you just spread it out a bit. Say you blow it up with an energy equal to its gravitational binding energy. All the bits get spread through the solar system and probably hit the other planets, but there's very little gravitational effect on them. Consider how little effect Jupiter's gravitation has on the earth's orbit.

Interestingly, there isn't any way to prove that a solar system with more than one planet is actually stable anyway. Given enough time, the perturbations caused by all the other planets' gravity could nudge one out of it's orbit and maybe eject it from the solar system (unlikely, but possible). This doesn't get any more likely if you remove one of those planets, however.

28-11-2007, 14:40
regardless the scale of time required would be massive to see any lasting damage (appart from flares).

The mass thing is important, if you blow up a planet the mass remains and is re-distributed, but the overall effect of the mass is the same. Its still there, cept not its a asteroid belt.

in the grand scheme of things the "wobble" would probably reduce as the mass is spread out and the star would wobble less. Its not going to suddenly spazz out and spin faster or anything, not perceviably to us anyway. Were talking hundreds of billlions of years here for a solar systems lifetime.

max the dog
28-11-2007, 15:16
I think Aasimov did a calculation on destroying a planet like earth in a Star Wars Death Star type of attack and it required more energy that all the suns in the galaxy combined. So we can eliminate that option.
Of course you don't have to vaporize a planet to destroy it to a civilization. The idea of messing with it's orbit does have some merit. Moving the earth outside of it's habitable zone would be just as destructive as a major impact. The idea is not that impractical for an advanced civilization. I can't remember the name or author of the book but I read a fiction where humans terraformed a planet by moving it into the habitable zone around a star. They never actually moved the planet it'self directly but instead moved many other smaller objects to pass nearby and slow it's orbit. It would sling the smaller object out of the system and give the larger planet a slightly slower orbit closer and closer to the star. They did it a few thousand times and the larger planet moved into a shallower orbit and warmed up. If one could move a planet into a habitable zone they could also move it out of a habitable zone. The advantage is that the planet is largely intact and could be moved back into the correct orbit one the war is over.

Comrade Wraith
28-11-2007, 15:30
I really have to agree with bobmbot here

A few intrestion visions of worlds blowing up can bee seen at the start of men in black 2, including a plantet with a moon in which the planet begins to implode, dragging the mooon with it then suddenly exploding.

Perhaps not strictly possible but fun to watch

28-11-2007, 15:35
You could render a planet effectively destroyed simply by putting a big shade between the planet and the sun (think Arthur C. Clarkes solar sail on this one). If no sunlight reached the surface, the planet would eventually get so cold that you might even get the atmosphere condensing. It's one of the suggestions for how we might terraform Venus one day.

If you blew the planet apart, the short term effect on the sun would be negligible, as the mass retains it's momentum relative to the sun. As time passed the orbital mechanics would work on the debris, and change the situation, but it would be a relatively gradual thing I believe.

Jo Bennett
28-11-2007, 15:39
I think Aasimov did a calculation on destroying a planet like earth in a Star Wars Death Star type of attack and it required more energy that all the suns in the galaxy combined. So we can eliminate that option.

I wouldn't be so sure, what you would want to do is convert a small percentage of the mass of the planet to energy, probably via a nuclear reaction, and use that to blow apart the rest. Focussed radiation on the planet's core might do the trick.

de Selby
28-11-2007, 16:18
I think Aasimov did a calculation on destroying a planet like earth in a Star Wars Death Star type of attack and it required more energy that all the suns in the galaxy combined. So we can eliminate that option.

I went to wikipedia to check the necessary figures to estmiate the binding energy for myself, and found someone had already done it for me:

Assuming that the Earth is a uniform sphere (which is not correct, but is close enough to get an order-of-magnitude estimate) with M = 5.971024kg and r = 6.37106m, U is 2.241032J. This is roughly equal to one week of the Sun's total energy output. It is 37.5 MJ/kg, 60% of the absolute value of the potential energy per kilogram at the surface

I make that about a million million (ie. 10^12) metric tons of antimatter, or maybe two million billion metric tons of fissile material (nuclear warheads). It's definitely overkill. Much simpler to re-surface the planet with a passing asteroid.


28-11-2007, 17:07
Yes the mass would still be there but i always imagined that the wobble is like someone throwing a hammer in sports, the mass drags the person round but if it were redistributed in a ring like asteroid belt the pull on the star would be diminished as it would not be concentrated in one point

de Selby
28-11-2007, 17:22
That's all true but it's really tiny. That's why earthlike planets are so hard to detect by 'wobble'. If we're talking about influencing the suns dynamics, we're talking about the relaxation of tidal forces, which are already variable (acting towards each planet, all of which are in motion and which do not rotate with the rotional period of the sun itself) anyway.

28-11-2007, 17:33
A planet going round a star isnt anything like the hammer throw in the olympics.
It's more like instead of a hammer you have a bit of fishing wire and a pea strapped to the end.

You have to factor in the fact that there is more than 1 planet likely to be going around that sun, and they arent all in the same place.
Plus a planet has a pretty neglible mass compared to the average star.

Assuming you can actually wipe a planet out and cause its mass to effectively disappear such a weapon would be of far greater effect if used on the star.
Remove the star and that causes all sorts of really bad things to happen.

28-11-2007, 17:33
If the planet "exploded" in some manner, the centre of the mass would be unchanged. If you also conceived to alter the path of the centre of mass, then the effect on the sun would be proportionate to that - but not necessarily that much.

Remember that the largest "wobble" - that of a hot Jupiter (a large gas giant in a close orbit) - is still very small. It's less like someone throwing a hammer, and more like swinging a tennis ball around on a shoelace (if that). The Earth would be more like a ping-pong ball on a piece of fishing line. If someone cut the line, you might notice, but you wouldn't fall over (not unless you really, really sad that someone cut your best piece of fishing line).

EDIT: Great minds think alike, theunwantedbeing...

28-11-2007, 18:31
Just remembered something i know its not scientific but in star trek 2 isnt khan on a desert world that used to be a lush world and its changed because the neighbouring world was destroyed and shifted their planets orbit.
Not really scientific but it was kinda like what i was meaning

Comrade Wraith
28-11-2007, 18:47
Tallarn was like that, and destroyed by virus bombing from the (iron warriors?), exterminatus on that meaning is quite possible given the right amount and type of weapons

05-12-2007, 19:48
anyone mentioned this (http://qntm.org/?destroy) yet? it's a seriously good read!

06-12-2007, 08:38
anyone mentioned this (http://qntm.org/?destroy) yet? it's a seriously good read!

There's some great stuff in there. Thanks for sharing!

06-12-2007, 10:06
Planets are much smaller than stars. Even the largest planet in our Solar System, Jupiter, is still much, much, MUCH smaller than our Sun.

I don't think that, if a planet was suddenly destroyed, it would effect the star much (Maybe a flare more than normal) but it would have much more effect on the other planets in the Solar System. Doesn't Jupiter's gravitational pull keep most asteroids from hitting Earth?

06-12-2007, 11:00
Isn't Jupiter's mass not that much less than the amount required for a body to form a small star though? I'm sure I read that somewhere.

06-12-2007, 11:11
Isn't Jupiter's mass not that much less than the amount required for a body to form a small star though? I'm sure I read that somewhere.

The amount of mass required to form a star is estimated to be about 75 times that of Jupiter, at least (wiki (http://http://en.wikipedia.org/wiki/Star)). Our own sun is roughly 1000 times as heavy as Jupiter. It is still quite a difference.

But it is a mood point, really. If you could somehow make Jupiters mass dissapear suddenly, you would have probably have enough energy to just directly blow up the sun, instead of destabilizing it a bit.

Chaos and Evil
06-12-2007, 12:31
This is worth posting: http://www.youtube.com/watch?v=93dIYwQ6m5M

06-12-2007, 16:43
Isn't Jupiter's mass not that much less than the amount required for a body to form a small star though? I'm sure I read that somewhere.

I think you got that from the fact that in one of Arthur C. Clarke's Space Odyssey series of books, Jupiter gets turned into a star. But that's managed by pseudo-science machines which probably wouldn't work in real life.