"Independence Day": Core Values

They're baaaaack. Just when you thought humanity's future was already dimmed with tough problems like climate change, terrorism and reality TV, bad guys from a distant planet show up to ruin everyone's whole summer. It's "Independence Day: Resurgence."

What's the deal? It seems that the invading aliens, with their ugly praying mantis heads and restless flagella for swatting flies, are here for... our planet's core. That's right: They've come to pump out the Earth.

Two decades ago these same aggressive aliens swooped down on our planet like space-faring locusts, to stripmine our resources and obliterate life. Not the gentlest of agendas for sure. One of the truly memorable lines in the original "Independence Day" was uttered when the U.S. president, clearly discomfited by the havoc and destruction, asked these unattractive creatures "What do you want us to do?" The answer was both candid and concise: "Die."

Bummer. But twenty years later, getting rid of us is not what drove them to drive here. They want Earth's core as an energy source for their spacecraft.

Now that's an interesting idea that might qualify as the mother of all fracking schemes. But what in Earth's core could interest these interstellar insectoids anyway? Is there some terrific source of energy hunkered down in our planet's hot-and-heavy center?

Well, since the 1930s we've known that there are actually two cores down there, imaginatively known as the inner and the outer. Both are mostly metal -- iron and nickel. Thanks to the pressure of all that's above it, the inner core is a solid sphere about 1500 miles in diameter. It's a hot, supersized cannonball that would be difficult to pump out, for sure. Imagine trying to get the pit out of an avocado with a hypodermic needle.

The outer core, a gooey layer roughly 1,400 miles thick that surrounds the inner core, is liquid and less dense. Not liquid like water of course, but more akin to the hot magma that oozes out of volcanoes. It's this layer -- one presumes -- that is the target of the aliens' unauthorized drilling project.

But how do you power your interstellar spacecraft with molten metal? Iron, it turns out, is the most stable of the elements -- you can't fission it or fuse it. But of course there is all that heat energy, given that the outer core is a scalding 7,000 F or more. You can compute just how much heat energy we're talking about using nothing more than freshman physics, and it works out to 800 thousand joules per pound.

Admittedly, that's not a number you'll be bandying about at the water cooler, but I urge you to compare it to the energy per pound of regular-test gasoline, which is 22 million joules.

In other words, this is more than a misguided alien attempt to purloin low-test fuel from Earth: they're going for no-test.

Clearly, this doesn't make too much sense. (Which could be said of the aliens' military technologies, too. But there's no time for that now.)

Then again, let's be fair: There aren't many movie-goers who expect "Independence Day" to be an extra credit exercise in STEM education. And frankly, leaving aside all the funky science, the cosmic-scale visual imagery of this sci-fi potboiler is worth the admission. For fans of the original film, there's the pleasure of seeing the always-compelling Brent Spiner topped by his now-trademark Leonardo da Vinci hairdo. And everyone can enjoy the offhand personality of Jeff Goldblum who, I note, is still able to amble double-jointed into any scene.

Undoubtedly you'll sleep better at night knowing that Earth's core -- while handy for keeping our planet's magnetic field going -- is unlikely bait for mucus-riddled visitors from afar. Just keep them away from your local service station.