Planet Destroyers

[sir_pudding]

Originally Posted by Ragabash Moon

Yes, I did read your entire post. What would be the point of damaging Yavin? Whether the laser damaged it or not, it wouldn't destroy it, which is the whole point.

Okay, once again this thread is not about the Death Star(tm), it's about any attempt to kill a planet. Maybe it's about a setting where gas giants are inhabited by gravitational/magnetic feild entities(one of Benford's Galatic Center books IIRC) or sentient nanotech colonies (Cassini Division) and somebody wants to kill them. Maybe it's about what happens in a hard-sf setting when a relativistic spacecraft collides with a planet. It doesn't really matter.

Originally Posted by whswhs

The earth has both HP and DR. The HP come from the total mass, which you can get from density and radius. But the DR appears to come from the crust, which is a fairly thin layer of rock. Once you get through that, you're dealing with fluid material most of the way down.

Yes that's where I got my numbers:
1.6 billion HP based on mass
DR 25 million based on the 50mile average thickness of the crust and using the low end DR for stone (since the crust is mostly basalt).

Because the structure of the Earth is differentiated does that mean it's Unliving rather than Homogenous?

The collision:
A 1000 ton spacecraft (500HP) travelling at .7c(~230,000,000 yds/sec) collides with the Earth. It inflicts 1,150,000,000d to the Earth, with an average of 4,025,000,000 points of crushing damage. 4,000,000,000 points penetrate DR, putting the Earth at -2.4 billion HP, which is -1.5 x HP, Earth must make a HT roll to avoid destruction. What 0 HP and less (HT roll once per second while under stress and "in use") means for a planet is unclear, perhaps a failed HT roll means it is rendered unihabitable, or it is torn apart by gravitational stress.

[lwcamp]

Originally Posted by sir_pudding

1.6 billion HP based on mass
DR 25 million based on the 50mile average thickness of the crust and using the low end DR for stone (since the crust is mostly basalt).

If you do this much damage, you will have broken the planet into pieces - probably several large chunks plus multiple smaller bits. However, while you may have smashed it up pretty good, you will not have destroyed it as a planet. The reason is because those chunks and bits are still attracted together by their mutual gravity and will quickly coalesce into one large lump of metal and rock once again (granted, it will be molten rock even at the surface). To make it into something that is no longer a planet, you have to deliver enough energy to overcome the gravitational binding energy of the planet. This requires about 2.4 x 10^32 Joules, or the energy equivalent of the complete annihilation of about 3 trillion tons of antimatter with an equal amount of matter. Using the formula for damage from explosives, this means it will take something like a 6d x 2.2 x 10^13 explosion to blast the earth into bits that will not fall back together and coalesce into a planet once again. You thus need on the order of 40 trillion points of damage to truely destroy a planet.

Of course, merely wiping out all life on the planet is much, much easier. Melting the entire crust into molten magma takes far less damage.

Luke

[CraigR]

Of course, to get a good treatise on what it would take to destroy the Earth, you should go here.

[sir_pudding]

Originally Posted by lwcamp

If you do this much damage, you will have broken the planet into pieces - probably several large chunks plus multiple smaller bits. However, while you may have smashed it up pretty good, you will not have destroyed it as a planet.

Well, nobody is going to be living there for a while.

The reason is because those chunks and bits are still attracted together by their mutual gravity and will quickly coalesce into one large lump of metal and rock once again (granted, it will be molten rock even at the surface).

Quickly in geological time, or historical time?

[lwcamp]

Originally Posted by sir_pudding

Quickly in geological time, or historical time?

A few hours at most, although some debris may remain in orbit and form a ring system or a new moon.

Luke

[sir_pudding]

Originally Posted by lwcamp

A few hours at most, although some debris may remain in orbit and form a ring system or a new moon.

Luke

How long until it's habitable?

[Fabricati]

Originally Posted by sir_pudding

How long until it's habitable?

Okay, so you 'killed' the planet, but you didn't completely annihilate it. That requires going to -10xHP which is probably some ridiculous amount of energy (The aforementioned 10^32?).

[lwcamp]

Originally Posted by sir_pudding

How long until it's habitable?

Give it a million years or so to cool off and form a solid crust, and for the vulcanism to subside to something reasonable. Then you've got a thick atmosphere of all the gases that escaped the mantle that you need to get rid of. Since you've sterilized the planet, you don't have life to do that for you, and right now it is anyone's guess as to how long it takes life to evolve.

Luke

[sir_pudding]

Originally Posted by Fabricati

Okay, so you 'killed' the planet, but you didn't completely annihilate it. That requires going to -10xHP which is probably some ridiculous amount of energy (The aforementioned 10^32?).

According to Luke it's more than -10xHP that would only be 17.6 billion points of damage, he's saying it's more like 40 trillion.

[Bruno]

<nukes yet another comment about -10xHP>

Woops, that's what I get for being quick on the quote button. Comment retracted for redundancy.