# How Could We Destroy the Moon?

What would it take to destroy our moon, and eliminate the enemy of stellar astronomy for all time?

In the immortal words of Mr. Burns, “ever since the beginning of time, man has wished to destroy the Sun.” Your days are numbered, Sun.

But supervillains, being the practical folks they are, know that a more worthy goal would be to destroy the Moon, or at least deface it horribly. Nothing wrecks a beautiful night sky like that hideous pockmarked spotlight. What would it take to destroy it and eliminate the enemy of stellar astronomy for all time?

Crack out your Acme brand blueprint paper and white pencils, it’s Wile E. Coyote time.

The energy it takes to dismantle a gravitationally held object is known as its binding energy, we talked about it in a Death Star episode and inventive ways to overcome it.

For example, the binding energy of the Earth is 2.2 x 10^32 joules. It’s a lot. The binding energy of a smaller object, like our Moon is a tidy little 1.2 x 10^29 joules. It takes about 1800 times more energy to destroy the Earth than it takes to destroy the Moon.

It’s 1800 times easier. That’s downright doable, isn’t it? That’s almost 2000 times easier. Which, on the scale of easy to less easy, is definitely closer to easy.

Take the event that created the Caloris Basin on Mercury. It’s a crater, 1,500 km across. Astronomers think that a big fat asteroid, a fatsteroid(?) around 100 km in diameter crashed into Mercury billions of years ago. This event released 1.3 x 10^26 joules of energy, carving out this giant pit. It’s a thousandth of the binding energy of the Moon. We’ll need something more.

Our Sun produces 3.8 x 10^26 joules of energy every second, the equivalent of about a billion hydrogen bombs. If you directed the full power of the Sun at the Moon for 15 minutes, it’d tear apart.

That’s quite a superweapon you’ve got there, perhaps you’ll want to mount that on a space station and take it for a cruise through a galaxy far far away?

If that scene took that long, we’d have fallen asleep. It’s as if millions of voices gradually became a little hoarse from crying out for a quarter of an hour. There’s another way you could tear the Moon apart that doesn’t require an astral gate accident: gravity.

Astronomers use the Roche Limit to calculate how close an object – like a moon – can orbit another object – like a planet.

This is the point where the difference between the tidal forces on the “front” and “backside” are large enough that the object is torn apart, and if this sounds familiar you might want to look up “spaghettification”.

This is all based on the radius of the planet and the density of the planet and moon. If the Moon got close enough to the Earth, around 18,000 km, it would pull apart and be shredded into a beautiful ring.

And then the objects in the ring would enter the Earth’s atmosphere and rain down beautiful destruction for thousands of years.

Fortunately or unfortunately, depending your position in this “Die Moon, Die” discussion, the Moon is drifting away from the Earth. It’ll never be closer than it is right now, at almost 400,000 km, without a little nudge.

Phobos, the largest moon orbiting Mars is slowly approaching the planet, and astronomers think it’ll reach the Roche Limit in the next few million years.

It turns out that if we really want to destroy the Moon, we’ll need to destroy all life on Earth as well.

## 22 Replies to “How Could We Destroy the Moon?”

1. elvigy says:

What about antimatter? You wouldn’t need an entire moon’s worth to create a big enough explosion to destroy the moon. Still a lot though. And then you have to store it and aim it at the moon. But if you’ve figured out how to make that much, the rest should be easy.

1. elvigy you’d need at least ~1 billion tons of antimatter, then fire it (somehow) into the Moon’s Core. To destroy the Earth, in Greg Bear’s “Forge of God”, aliens use two opposed chunks of neutronium/anti-neutronium that slowly spiral together inside the Earth, since they’re too dense to react (much) with normal matter. The “dense” interior of the Earth slowly slows the chunks into mutual collision. A similar trick could be done with the Moon – two separate billion-ton chunks of quark & anti-quark matter are then required, as neutronium is unstable except inside neutron stars.

2. Aqua4U says:

It used to be, “Let’s all go to the Moon…” Now it’s, “Let’s blow up the moon!” Say what? Are you upset about not being able to walk on the moon in your generation? SO AM I! Push the button!

3. mewo says:

Why would we want to blow up the Moon?

Yeah, let’s blow up Pluto.

1. robotopia says:

I vote to blow up ‘Goofy, Donald and Mickey all with Pluto!’

2. Qev says:

To make the Earth a more perfect sphere, once we’ve paved the entire surface, for maximally-ideal driving conditions in our Mach 6 Hypercars.

Anyway, we could just set up a momentum transfer system using repeated passes by smaller solar system bodies like asteroids. It would take a while, but it would be no problem to crash the Moon into the Earth or fling it out of orbit.

3. robotopia says:

It’s blocking my view of Mercury; It has to go.
Oh, and it might get rid of that Secret Alien Moon Base that nobody is supposed to know about… Oops… Nevermind!
I didn’t write that… I was never here.

4. Aubri says:

“Court is now in session, Judge Gravity presidin’. ALL RISE.”

It seems we’ve skipped a step, here. You calculated the gravitational binding energy of the Moon, but not the energy required to lower its orbit to the Roche limit. I think I’ll take a crack at it.

Fortunately, I don’t need to do the heavy lifting on the physics, because Rhett Allain already did it over here: http://www.wired.com/2010/11/changing-orbits-and-changing-speed/
Long story short, the change in energy (dE) required to change orbital radius from r1 to r2 is:
dE = 1/2*G*m*Me( (r2-r1) / (r1*r2) )

Plug in the Gravitational Constant G=6.674×10^-11 N*m^2/kg^2, the Moon’s non-negligible mass of m = 7.3477×10^22 kg, and Earth’s mass Me=5.97219×10^24 kg, and we have
dE = 1.46433768365031×10^59( (r2-r1) / (r1*r2) )

Our starting radius is the Moon’s current average orbital radius in meters (r1 = 384,399,000 m), and our ending radius is the Roche limit for the Moon (r2 = 18,000,000 m). When I plug those in, I get
dE = -7.754×10^51 J. (The value is negative because the Moon has to lose this energy to descend in its orbit.)

So, in short (too late!) while gravity will do the work of actually disassembling the Moon for you, getting the Moon down to its Roche limit will cost TEN SEXTILLION times more energy than just blowing the thing up!

1. You’ve computed the wrong value, somehow. It’s actually -1.55E+30 J. Only ~12 times the Moon’s binding energy.

1. Of course, to cause the escape of the Moon only needs 7.62E+28 J.

2. Aubri says:

Can you see where? I thought 10^51 seemed high, but I ran the numbers three times and kept getting the same thing…

3. You’ve used 6.674E+11 as G instead of 6.674E-11. And my own calculation was for the difference in potential energy between altitudes, not for orbitting satellites. So it’d be just 7.75E+29 J, not 1.55E+30. My mistake.

4. Aubri says:

Ah, dang it. That was it. Thanks!

5. BlackWolfStanding says:

Thrust over time and accelerate the moon out of orbit. It’s slowly heading that way anyways. Let’s just give it a nudge so that it could happen before the Sun goes into it’s Red Giant phase.

6. LapsedPacifist 2 says:

“Nothing wrecks a beautiful night sky like that hideous pockmarked spotlight. What would it take to destroy it and eliminate the enemy of stellar astronomy for all time?”

It would be easier and less expensive just to put your observatory on the far side of the Moon. As a bonus, that would make the Sun much less of a bother too. And you could dispense with those expensive adaptive optics.

1. Aqua4U says:

“…observatory on the far side of the Moon…” I vote yes! Find the appropriate size and shape crater. Level the tops of the crater walls where necessary then build a REALLY big, suspended like Arecibo, radio telescope! How about… after the ISS has finished it’s primary mission. We disassemble and send the usable modules to lunar orbit? Reassemble.. resupply.. and reuse as a trans lunar way station? Might be the Russians will do that?

7. N70SAK says:

You can ruin the resale value by blasting your name in it with a big laser. 🙂

1. robotopia says:

Yeah, but at least the Martians will no longer want to buy it and build time-shares there. And think of the ore we could mine until it blows up on its own!

8. robotopia says:

Send 3 different Spacecraft to the Moon; One with a payload of just ‘Pure Sand’, another with a payload of just ‘Pure Aluminum Powder’. The Third Spacecraft I come back to later. Once there, there would need to be a way to combine the two payloads ands sift thoroughly, but not too much. Once the Two components are “sifted well’, divide in half, place each half into the two spacecraft and set on on the light-side and the other on the relative polar-opposite of the location of the first craft. Now set two precisely-synchronized timers on each payload and get your crew back into the Third craft to scram and wait… when the timers hit the ZERO-Mark (hopefully in sync), you have a massive “Super-Thermite” Explosion. If there’s any debris (And it seems there will be) THAT’S Another issue you can resolve with another question on another day. FYI: once the said “Moon” is gone, What would the Effects of its just not being there have upon the Earth?! –Aside from the explosion itself and the debris, the fact that the usual gravitation effects that the moon has or had on the Earth would be gone, could be a big concern.
( *Your Welcome… from Your Friendly ‘Local Union of The Vogon Constructor Fleet’. We make it Done Blow-Up Good; Note: We Don’t Do Clean ups. That’s Another Dept. and They Aren’t Union*. )

9. Gaugain says:

you`re crazy everyone… easiest way is to use (harvest) the work of the best scientist of CERN, a small Black Hole (their dream product) …Just send it there, it will swallow the Moon, it will still be there circling the Earth, but you won`t see it , so job done…Plus you`ll have the best garbage collector ever for the radio-waste products from the nuclear power plants…no more dang light over your telescopes watching Jupiter`s spot…