## 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.

## What is a Joule?

When we raise an apple up to a height of one meter, we perform approximately one joule of work. So what is a joule?

Joule is the unit of energy used by the International Standard of Units (SI). It is defined as the amount of work done on a body by a one Newton force that moves the body over a distance of one meter. Wait a minute … is it a unit of energy or a unit of work?

Actually, it is a unit of both because the two are interrelated. Energy is just the ability of a body to do work. Conversely, work done on a body changes the energy of the body. Let’s go back to the apple example mentioned earlier to elaborate.

An apple is a favorite example to illustrate a one joule of work when using the definition given earlier (i.e., the amount of work done ….) because an apple weighs approximately one Newton. Thus, you’d have to exert a one Newton upward force to counteract its one Newton weight. Once you’ve lifted it up to a height of one meter, you would have performed one joule of work on it.

Now, how does energy fit into the picture? As you perform work on the apple, the energy of the apple (in this case, its potential energy) changes. At the top, the apple would have gained about one joule of potential energy.

Also, when the apple is one meter above its original position, say the floor, gravity would have gained the ability to do work on it. This ability, when measured in joules, is equivalent to one joule.

Meaning, when you release the apple, the force of gravity, which is simply just the weight of the body and equivalent to one Newton, would be able to perform one joule of work on it when the apple drops down from a height of one meter.

Mathematically, 1 joule = 1 Newton ⋅ meter. However, writing it as Newton ⋅ meter is discouraged since it can be easily confused with the unit of torque.

Particle physics experiments deal with large amounts of energies. That is why it is also known as high energy physics. If you liked our answer to the question, “What is a Joule?”, you might want to read the following articles from Universe Today:

Rare Binary Pulsars Provide High Energy Physics Lab
New Particle Throws Monkeywrench in Particle Physics
Physics World also has some more:
Particle physics: the next generation
To the LHC and beyond
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:
The Large Hadron Collider and the Search for the Higgs-Boson
Antimatter