Guest Post: Blowing Up Planets

by Nathan Bergey

Nathan BergeyDoomsday scenarios are a dime a dozen. When a villain claims to be on the verge of ‘destroying the Earth’ he/she usually means killing everyone/everything on it. But sometimes simply killing all humans isn’t good enough. Unfortunately even the vast amounts of energy necessary to wipe out all civilization is woefully inadequate to physically destroy the planet. To do that would take some serious power.

Planets Die Hard

The Earth has been here for about 4.5 billion years. Nothing yet has been able to destroy it, including being slammed into by another planet. Why is it so hard to destroy? The short and somewhat obvious answer is Earth is big—really big. And if you simply break it into a bunch of pieces it will just fall back together again because of gravity. In order to really destroy it you have to break it up and then fling to pieces away at a high enough speed such that they will never come back together (escape velocity). This requires going above and beyond with one’s diabolical destruction schemes.

Energy

To get a rough gauge on how much energy you need to blow up the whole Earth we can treat the Earth as loose bunch of particles held together by gravity. The energy required to pull them apart and fling them away fast enough that they never come back is called the gravitational binding energy. For the Earth this is about 2.24 × 1032 joules. But the Earth is not just held together by gravity. It has a solid crust and liquid interior with surface tension. These are electromagnetic forces called van der Waals forces. I have yet to find a good estimate for the energy required to break the Earth apart in to a collection of gravitationally bound particles, but we can guess. Lets make things simple by just melting it, rounding up and hoping that’s good enough for the gravitational binding energy to do the rest.

It takes about 900 kilojoules to melt one kilogram of crust. There is about 1.365 × 1023 kg of mass in the crust. The rest is mostly molten already. So it would take something like 2.0 × 1029 joules to melt the Earth. It turns out that This is significantly less than the gravitation bounding energy. So we still are left with about 2.24 × 10 32 joules as the minimum necessary energy to destroy the Earth. Any scheme we can think of will likely be less than 100% efficient (high energy explosions require all the heat and particles to be completely absorbed, this rarely happens). Lets just say 10% efficiency and round up and say we would need to somehow get 3.0 × 10 33 joules.

What Can Do This?

Well, nukes are out. The amount of energy we’re talking about is about 70,000,000,000,000 10-megaton nuclear bombs. That’s about 2 billion times more nuclear bombs than we currently have on this planet. So what can we use instead?

Antimatter is a good candidate. Even with E=mc2 on your side it will still take 300 billion kgs of antimatter to get a big enough blast. We currently seem to be able to make antimatter a few particles at a time. So this is only doable if you have some fancy antimatter making machine.

Lasers also don’t seem up to the task. How exactly a laser would distribute it’s energy across the whole planet isn’t clear to me. Besides that you need to turn store up a huge amount of energy and release it all at once. It’s hard to do this without burning up the laser itself. The National Ignition Facility uses a bank of capacitors filling a stadium sized building. And yet it only has 1/1024 the power necessary.

Slamming it really hard with another planet. Well, this has happened before with no success. All we got was a moon. But if a Mars sized object was moving at 220,000 mph and transferred all it’s energy to Earth that should do the trick. Good luck accelerating a small planet to 220,000 mph though. Perhaps a crafty orbit getting flyby boosts from nearby stars? This has the other disadvantage of having to have good aim. Just like avoiding asteroid collisions a small orbital correction done early enough can cause an object to miss Earth by thousands of miles.

Supernova if right next to the Earth should do the trick, but moving stars is harder then just blowing up the Earth in the first place. Now if you can create a supernova in the middle of the Earth you get bonus points! This would require putting about 3 solar masses in a tight ball in Earth’s core.

Just Hurl It Into the Sun

Instead of blowing up the Earth directly you could also just toss it into the Sun. In fact the Sun has more than enough energy to totally vaporize the Earth, though just not all at once. It would take a few months. Still, destruction is pretty much guaranteed. For the supervillain on a budget it actually turns out to take less energy to throw the Earth into Jupiter! This is because you have to slow down the Earth from it’s current solar orbital velocity (67,000 mph) to almost 0 for it to fall into the Sun, but you only have to accelerate it another 19,800 mph to get it out to Jupiter. Jupiter won’t vaporize Earth but it will swallow it up and incorporate it into it’s core. Accelerating a mass the size of the Earth 19,800 mph to get to Jupiter would take approximately 10 19 Saturn 5 rockets all firing at once.

No wonder the Death Star was the size of a moon.


Nathan Bergey is a rocket scientist. He constantly thinks about the future of space travel and helps build advanced amateur rockets at Portland State Aerospace Society—pushing the envelope of low cost rocket technology. He also writes about science and tech (and random things) at his blog Mechanical Integrator and writes a monthly column for the Clarion Foundation blog, which is where this post originally appeared. He can be found on twitter as @natronics.

8 Responses

  1. Ana Steuart

    Hi there. I’m a textbook editor, and in reading your article, I realized you’re missing some formatting. 2.24 x 1032 should be listed as 2.24 x 10^32 to shot that 32 is an exponent of 10 in Scientific Notation. Or you could be fancy and use the [sup] tag to properly express 2.24 x 1032.

  2. Jeff WIlson

    I believe it’s correct to discount the Van Der Waals forces for another reason, in that it would scale based on the newly exposed surface area of the pieces to which the earth was reduced. This could be as little as two halves if some sort of finely bounded field of body forces were involved, but the square-cube law makes it a tiny consideration compared to the the volume-scaling mass’s gravitation.

    However, you might want to apply additional kinetic energy to accelerate the pieces to solar escape velocity @ 1 AU, lest the ring of fragments left in earth’s former orbit eventually reassemble into one or more successor bodies.

  3. James Davis Nicoll

    One of
    these orbiting a sun-like star can do the job but it will take at least a week to evaporate the Earth and probably more.

  4. Gareth Owens

    Planets get blowed up in SF all the time. I can think of four off the top of my head: Alderan in Star Wars – both Loki VI and Kilra in Wing-commander 3 (Mark Hamil getting a taste for blowing stuff up there) and there was that planet of the casino hive in the original Battlestar Galactica.
    That, for me, is sort of the point. SF isn’t about what scientists can do – I know you can’t blow up a planet…boring! – but SF is about what the imagination can do – but wouldn’t it look cool if you could.
    If you limit your literary imagination to the merely possible then there would be no Star Trek – (Warp drive, do you know how much energy that needs, then there’s that whole inconvenience of relativity, and as for the data storage needed for transporter systems, and the quantum implications of matter transmission as a whole…)
    Reality is such a downer but SF doesn’t have to be, it merely has to be plausible within the context and duration of the narration.
    Don’t fetter Icarus.

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