How to fragment a moon to form a ring around a planet

Question

Given a planet about the size of Earth, and a moon the Size of the Moon, how could one destroy the moon without flinging the fragments onto the surface of the planet or into outer space?

How can one make the moon break up and form a ring around the planet, like Saturn did with his moons?

Answer 1

"All" you need to do is move the moon closer in towards the planet (without sending it into the planet or out of orbit).

Once the moon gets close enough and moves inside the Roche Limit it will be ripped apart by tidal forces and you can just sit back and let it happen. The fragments will form a ring by themselves. This is believed to be one of the main ways existing rings formed.

Answer 2

Moving the moon in to the Roche Limit, as Tim B suggested, is an excellent start. In the case of Earth, however, that involves lowering the moon's orbit to between 10 and 20,000 km (when it currently orbits at 360-400,000 km). Since this is low enough to interfere with the orbits of artificial satellites, it may be preferable to try to keep the debris ring higher than that.

To do that, we need to counteract some of the gravitational forces binding the moon together. That's straightforward enough - it just takes a really big bomb. Note, however, that in this case we don't want the bomb to be big enough to blow the moon apart properly. Instead, what we want to do is to make the explosion big enough to turn it into a cloud of rock fragments, but small enough that the cloud's gravity would eventually pull it back together again. If we get it just right, as the cloud gets close to its largest size tidal forces from the planet it orbits will kick in and start dragging off the inner layers. Once that process starts, the internal gravitational forces are no longer in control and the moon should disintegrate nicely.

There are a couple of ways to fine-tune the process. Moving the moon in closer to the planet is one - the closer you get, the stronger the tidal forces become, and the easier it is to prevent the moon from recoalescing. Secondly, you can play with the positioning of the explosives; your local astrophysicist or registered terraformer should be able to advise you on what shape debris cloud will be most useful.

Answer 3

Ok, I'll make that an answer.

Disclaimer: I am not a registered terraformer, consult your local registered terraformer before actually performing astroengineering works.

You cannot do. At least, you cannot say: "I will put my electroscientimagic device at point P, push button B at hour H and then I can call it a day".

What your elecroscientimagic device will do will be applying energy. That energy (minus inefficiences) will go into breaking the Moon (which by itself is not a big change) and giving the fragments enough energy to leave the Moon's gravity and get into Earth orbit.

Say you only make two halves and want one of each half in opposite points of the Moon's orbit. For the fragment you move, you need to:

• accelerate to Moon's (well, half-Moon) escape velocity.
• put in the desired point of the orbit.
• accelerate (o deccelerate) to the needed orbital speed to keep that orbit.

Now, by doing that change, you have changed also the center of masses, so you will have to adjust the orbit parameters of both halves of the moon.

To do your project, you will need to begin a long time process that will need constant supervision and readjustments. And of course, you will need some reason that justifies such effort.

Answer 4

You could certainly try.

A less sensible method, if your local astrotech store sells them, is to get hold of a mass transporter and a matter inversion matrix (though in many timelines the latter comes in around the year 4121). This would enable you to move dense objects such as small neutron stars around. If you can then vaporise the Moon's core as suggested in the comments (usually by introducing some intense heat to vaporise the rock inside), you would be able to move your neutron star into the core of the moon. This would collapse the moon. Soon after this (15 seconds or so), you use your matter inversion matrix to destroy the neutron star, causing a small explosion due to the lack of gravity (this is why you need to make sure to use a small neutron star).

Alternatively, if you don't have a ready source of intense heat, you could detonate a big bomb in the moon such that it expands for long enough to insert the neutron star, then the matter is pulled together again.

^{Disclaimer: This method does not guarantee all the fragments enter a ring, though most will. No responsibility can be accepted for damage to nearby planets from flying Moon fragments.}

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If you want to be more sensible, I suggest looking at Tim B's answer. The Roche limit is always a good way to destroy celestial objects. In fact, I think I remember the Varga using it to destroy Mercury in 3112...

Or, of course, just a really big bomb.