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Comment by jaysonelliot | Hacker News Reader

The main assumption that seems wrong to me is the idea that a massive energy weapon is even a good idea when it comes to destroying planets.

All you really need is a big enough rock to throw at it (apologies to Robert A. Heinlein).

A planetwide extinction event could be triggered with an asteroid just a couple dozen km in diameter. With a really big rock, say 400km across, you could boil off the oceans, according to Charles Cockell: http://books.google.com/books/about/Impossible_extinction.ht...

I imagine that even if a hyper-advanced Evil Empire wanted to vaporize a planet completely, it would be more efficient to push it off its orbit and into the sun than it would be to build a steel planet with a massive energy beam. And that's still ignoring all the other problems physics has in store for a planet-sized object that can be steered through space, enters other solar systems, and gets close enough to a planet to blow it up.

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In context, that is not true. In the Star Wars universe, planets have planetary shields, which are extremely powerful and able to take a lot of abuse. An asteroid strike is wildly less powerful than what the Death Star can inflict on a planet; ten+ of orders of magnitude, and I mean that fully literally. An asteroid strike may be enough to wipe out an unprotected civilization, but it hardly affects the planet underneath. The Death Star delivered enough energy to the target to undo the entire binding energy of the planet and completely disassemble it, and do it quite quickly. That's the difference between a very large nuclear strike, let's say 10^20J for roundness [1], vs. the binding energy of a planet, call it 10^32J, plus a great deal extra kinetic energy to blow the planet apart at a sufficient speed to satisfy Hollywood's need for instant spectacle.

For that matter, the canon specifications for a single turbolaser strike are on the order of what we'd associate with a very large nuclear event; if a planetary shield can withstand sustained bombardment by multiple Star Destroyers, moving an asteroid around isn't going to matter.

(One could discuss accelerating an asteroid to kinetic kill speeds, but if you can build a Death Star, it is certainly a lot easier to control and deploy.)

In real life, of course, with no plausible mechanism for anything like "shields" to exist, you are of course correct. If you're patient one can completely destroy all life on a planet with distressingly small investments of energy not entirely dissimilar to what we could produce today.

[1]: http://en.wikipedia.org/wiki/TNT_equivalent , I'm spec'ing out a ~20 gigaton strike here.

[2]: http://scienceblogs.com/builtonfacts/2009/02/the_physics_of_...

I love this debate.

You missed something: you can simply pulverize the asteroid with a ground based laser cannon. No need for shields.

It could take months or years for an asteroid strike to render a planet fully uninhabitable, and in a universe with large spaceships and hyperdrives, that means a reasonable survival rate via evacuation. So now you've committed to months and months of blockading the planet to prevent evacuation. At that point, why not just blockade the planet in the first place and wait until they run out of some sort of vital food/medicine/defense goods or the population just capitulates out of war weariness?

I agree with your core point, but a blockade would not work to destroy most habitable planets. Most habitable planets in Star Wars are at least capable of self sufficiency. You would hurt their economy certainly, but most could produce enough food and other necessities to maintain a (possibly diminished) society.

Coruscant is likely an exception. That one has been turned almost entirely into one city and has virtually no farmland, certainly not enough to support even a fraction of its population.

One wonders how a planet like Courscant, with a population exceeding a trillion, could possibly import enough food to maintain its population. Sure, in Star Wars we have cheap space travel, but there's still the difficulty of distributing everything at the space ports. Perhaps they have a large hydroponics system to supplement imports?

From what we've seen in the movies, the entire planet seems to have landing pads and such throughout the upper levels. If they've got a sizable fraction of the planet's surface area usable as a spaceport, distributed throughout essentially the entire planet, any logistical problems would not come from getting things between the spaceports and where they are needed.

"I imagine that even if a hyper-advanced Evil Empire wanted to vaporize a planet completely, it would be more efficient to push it off its orbit and into the sun than it would be to build a steel planet with a massive energy beam. And that's still ignoring all the other problems physics has in store for a planet-sized object that can be steered through space, enters other solar systems, and gets close enough to a planet to blow it up."

That would make for a particularly funny episode of Futurama. I could see some race destroying planetary systems using big planets and gravity to sling other planets into their suns. And only the Planet Express crew could stop them --- and maybe Zapp. <Kiff sigh />

Only evil bugs would resort to primitive tactics like that. Humans are more... civilized.

http://starshiptroopers.wikia.com/wiki/Meteor_attack_on_Buen...

I think that the Death Star was more of a Statement with a capital S than just a weapon. If you've read "Old Man's War", it's the evil equivalent of the orbital tether around Earth - not so much a convenient way of doing something (murdering a planet/getting into space) as a way of showing off.

Or a smaller rock moving really fast. "The Killing Star" describes it well, here is an excerpt: http://www.projectrho.com/rocket/spacegunexotic.php#id--Rela...

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