# "Independance Day" and the Earth's Atmosphere

You underestimate the size of the Moon. We have a mothership a quarter the size of the Moon. We’ll be generous and assume that means a quarter the linear dimension, not a quarter the mass, so it’d have a radius of 434 km. Assuming that it’s not just some big bubble, it probably has about the same density as water, giving it a mass of 3.410[sup]20[/sup] kg. Gravitational binding energy (the energy needed to blow up a gravitationally-bound object) is given by E = 3GM[sup]2[/sup]/(5R), so the mothership would require at least 10[sup]25[/sup] Joules to blow up. A megaton is 4.210[sup]15[/sup] Joules, so that means that it would take two and a half billion megatons to do the job. And that’s just assuming that the Mothership is held together entirely by gravity, without regard for any superstrong materials or forcefields the aliens might have. And while one may reasonably argue whether 100 megaton bombs exist, it’s quite certain that nobody has a billion megaton monster. Heck, all of the nuclear weapons in the world wouldn’t add up to that much.

For all you folks who are upset about the aliens being done in by a computer virus, I just wanna point out that Arthur C. Clarke did exactly the same thing in 3001: The Final Odyssey, which came out about the same time.

Of course, in that book the Earth folks had inside knowledge of the aliens’ computer system, which makes such a virus at least plausible. I still think it’s pretty unlikely.

I’ve always wondered about that, if such a thing did show up, wouldn’t it shift the Earth’s orbit a smidgeon or two?

I think that’s a really bad assumption. If you have defensive force fields, you don’t need to over build the structure to withstand big explosives. We build large structures that are overbuilt to withstand explosions: aircraft carriers. They quite obviously have a density significantly less than that of water.

They even show huge cavernous spaces inside the mother ship.

Seeing as how 500 megatons was already farfetched, a number greater than that would have been ridiculous.

As to whether 500 megatons would render the mothership incapacitated, I believe it would. Getting it up to space would be the biggest problem. The mothership was 500 miles across. A 500 megaton bomb would have a blast radius of 200 miles at least. Hell, 25 megatons has a 20 mile radius of extensive damage.

This place INSULTINGLY STUPID MOVIE PHYSICS has a pretty good explanantion of the physics impact of the huge alien ships.