# How many watts of energy would it take to vaporize an entire planet?

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Posted (edited)

Exawatt's? Zettawatt's? Yottawatt's? How much would it take, and could such energy be contained inside the hollowed out interior of a planet? And could it be fired from it?

Edited by daniel l.

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3 minutes ago, daniel l. said:

How much precisely would it take

What precicsely is this planet made of? What's it's mass? Current temperature? Distribution of elements? Internal structure?
You'll need to know all these things and more precisely if you want a precise answer.

7 minutes ago, daniel l. said:

could such energy be contained inside the hollowed out interior of a planet?

What kind of energy are you talking about? "contained" how?
If you're talking about the energy equivalent of the planet's mass, Einstein came up with an equation you have probably heard about... But hollow, as in totally empty space? That doesn't make sense.

8 minutes ago, daniel l. said:

And could it be fired from it?

I'm pretty sure this doesn't make sense... Fired? By what? As what? A stream of charged particles? Coherent laser light? Relativistic turkeys?

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Just now, steve_v said:

What precicsely is this planet made of? What's it's mass? Current temperature? Distribution of elements? Internal structure?
You'll need to know all these things and more precisely if you want a precise answer.

What kind of energy are you talking about? "contained" how?
If you're talking about the energy equivalent of the planet's mass, Einstein came up with an equation you have probably heard about... But hollow, as in totally empty space? That doesn't make sense.

I'm pretty sure this doesn't make sense... Fired? By what? As what? A stream of charged particles? Coherent laser light? Relativistic turkeys?

What I mean is, How much energy would it take to completely vaporize a planet about Earth size.

The energy I'm referring to would be a gamma ray laser. And by contained I mean the storage of the necessary power to generate such a laser, such as batteries or other.

And by fired, I mean to use that energy to generate the laser.

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Earth's gravitational binding energy is about 2.5E32 J. Watt is unit of power, which is energy transformed in time unit. Energy is power * time. 2.5E32 J is huge amount of energy. IEA estimated that in 2013 world's energy consumption was 3.9E20 J. If human's could use all energy they produce to send mass out of planet it would take 640 billion years to destroy planet. If it was possible to use whole Sun's power, 3.8E26W, to evaporate Earth, it would take 660 000 years.

We can also calculate binding energy per mass. It gives 42 MJ/kg. For example, TNT (and other typical high explosives used in mining or military applications) gives about 4 MJ/kg. If the Earth was made from TNT and it was exploded, gravity would pull combustion products back to spherical planet.

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1 minute ago, Hannu2 said:

Earth's gravitational binding energy is about 2.5E32 J. Watt is unit of power, which is energy transformed in time unit. Energy is power * time. 2.5E32 J is huge amount of energy. IEA estimated that in 2013 world's energy consumption was 3.9E20 J. If human's could use all energy they produce to send mass out of planet it would take 640 billion years to destroy planet. If it was possible to use whole Sun's power, 3.8E26W, to evaporate Earth, it would take 660 000 years.

We can also calculate binding energy per mass. It gives 42 MJ/kg. For example, TNT (and other typical high explosives used in mining or military applications) gives about 4 MJ/kg. If the Earth was made from TNT and it was exploded, gravity would pull combustion products back to spherical planet.

But what about a laser? How much power would it take for a gamma ray laser beam to vaporize an Earth-sized planet, and could such power be stored inside a planet that has had it's interior removed (The mantle and core removed and replaced with the machinery necessary.)

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Just now, daniel l. said:

such as batteries or other

Well then, you'd need to work out what kind of batteries...

As of our current technology, we have neither batteries nor lasers that could come close to a fraction of the energy required.

As for the original question, I don't know the precise composition of the planet of the top of my head, but if you take, say, metallic iron, a vaporisation energy of ~340 kJ/mol. Then you would need to get it's temperature, and use it's specific heat capacity to get current energy... work out how much more to reach that 340, divide by the efficiency of energy transfer from your gamma ray laser, work out how much is absorbed or reflected by the atmosphere (for which you will need the composition etc. of said atmosphere, wavelength of the laser, etc. etc.).
And that's just the iron core... There's also all that water and rock to calculate.
Blimey, what a lot of math. Think I'll go for a beer instead.

If I were you, I'd just pull a large number out of my behind. Precise is far too much work.

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Just now, steve_v said:

Well then, you'd need to work out what kind of batteries...

As of our current technology, we have neither batteries nor lasers that could come close to a fraction of the energy required.

As for the original question, I don't know the precise composition of the planet of the top of my head, but if you take, say, metallic iron, a vaporisation energy of ~340 kJ/mol. Then you would need to get it's temperature, and use it's specific heat capacity to get current energy... work out how much more to reach that 340, divide by the efficiency of energy transfer from your gamma ray laser, work out how much is absorbed or reflected by the atmosphere (for which you will need the composition etc. of said atmosphere, wavelength of the laser, etc. etc.).
And that's just the iron core... There's also all that water and rock to calculate.
Blimey, what a lot of math. Think I'll go for a beer instead.

If I were you, I'd just pull a large number out of my behind. Precise is far too much work.

Though, I heard somewhere that a Gigawatt laser could slice through 20ft of steel per second. I was just wondering what a zettawatt's worth of Gamma-Rays could do.

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Such a laser is pure science fiction. No known materials could be used to build it and no known means of store or transport energy could be used. You have to assume so many things against known natural laws that you can get any answer you want.

You need certain amount of energy. It is different than power. You can deliver certain energy in short time and high power or in long time and low power. For example, if your magical laser produced 1 s long pulse at 2.5E32 W average power, it would do the job (if we neglect dissipation). But you could also use 10 s long pulse at 2.5E31W or 100 s long pulse at 2.5E30W. Or 660000 years at 3.8E26W (which is Sun's output).

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Posted (edited)

12 minutes ago, Hannu2 said:

If the Earth was made from TNT and it was exploded, gravity would pull combustion products back to spherical planet.

And then there's the gravity problem... Even if you vaporized the planet, it'd just reform into a hotter planet under gravity...

4 minutes ago, daniel l. said:

Though, I heard somewhere that a Gigawatt laser could slice through 20ft of steel per second. I was just wondering what a zettawatt's worth of Gamma-Rays could do.

Er, 1x1012 more steel cutting?

Seriously though, this is all pure speculation. We don't even have a thoretical basis for building a laser that could vaporize a planet.

Just use a Phlebotinum cannon and be done with it.

Edited by steve_v
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Just now, steve_v said:

Er, 1x1012 more steel cutting?

Well. I figured if it could cut steel so quickly. Why not a planet?

I'm gonna cut to the chase here, could a planet killing laser weapon be theoretically stored within the hollowed interior of a planet?

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4 minutes ago, steve_v said:

As for the original question, I don't know the precise composition of the planet of the top of my head, but if you take, say, metallic iron, a vaporisation energy of ~340 kJ/mol.

Planet's gravitational binding energy is about an order of magnitude larger than energy needed to vaporize all mass. Probably any process which would produce enough energy to break gravitational bind would also vaporize material. If our magic laser would only vaporize all mass but not give enough energy to escape, it would stay a gas planet. Excess energy would be radiated during long time and the planet would cool down and condense again.

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Posted (edited)

5 minutes ago, daniel l. said:

I'm gonna cut to the chase here, could a planet killing laser weapon be theoretically stored within the hollowed interior of a planet?

As we have no idea how such a laser would be constructed, or what it would be made of, theoretically doesn't really apply. It's a pure sci-fi device.
I'm tempted to say yes, but it'd have to be made of, and powered by, something we haven't yet invented.

Edited by steve_v

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1 minute ago, daniel l. said:

Well. I figured if it could cut steel so quickly. Why not a planet?

I'm gonna cut to the chase here, could a planet killing laser weapon be theoretically stored within the hollowed interior of a planet?

It would be possible to produce energy needed, but not hide it inside a planet or any other structure made of any known material obeying known natural laws. If a neutron star or a black hole would make a near flyby, tidal forces would rip the Earth. Material would be vaporized and ionized to plasma at huge temperatures. Part of it would fall to star, part of it would be converted to radiation energy and part of it would be left as a small cosmic gas cloud.

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Just now, steve_v said:

As we have no idea how such a laser would be constructed, or what it would be made of, theoretically doesn't really apply. It's a pure sci-fi device.

Alright. I was just asking for the sake of a science-fiction idea I had. Imagine a future where the planets are converted into spacecraft with hollow interiors to fit the machinery necessary for interstellar flight. And the majority of humanity occupies Dyson sphere's instead.

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Posted (edited)

4 minutes ago, daniel l. said:

Imagine a future where the planets are converted into spacecraft with hollow interiors to fit the machinery necessary for interstellar flight. And the majority of humanity occupies Dyson sphere's instead.

Insert magically strong materials (dyson sphere) and handwavium drive (moving planets between solar systems), then a ridiculous phlebotinum powered laser fits right in.

The first step is inventing the materials and energy sources...

Edited by steve_v

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Just now, steve_v said:

moving planets between solar systems

A Dyson sphere according to the actual theory of Freeman Dyson is not a solid shell, rather a tightly knit swarm of spacecraft.

And to move a hollowed planet all you need a is a bigass EmDrive.

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Just now, daniel l. said:

A Dyson sphere according to the actual theory of Freeman Dyson is not a solid shell, rather a tightly knit swarm of spacecraft.

Hmm, I thought that was a Dyson swarm, bugger.

1 minute ago, daniel l. said:

And to move a hollowed planet all you need a is a bigass EmDrive.

And the energy source to power such a thing? Not to mention an EmDrive that scales to such a size...
And the ability  to "hollow out" a planet to begin with...
Still firmly in the realm of science fiction. I suggest nicking some ideas from that field.

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Just now, steve_v said:

Hmm, I thought that was a Dyson swarm, bugger.

And the energy source to power such a thing? Not to mention an EmDrive that scales to such a size...
And the ability  to "hollow out" a planet to begin with...
Still firmly in the realm of science fiction. I suggest nicking some ideas from that field.

If there was a society that was sufficiently automated as to just order the drone swarm to do whatever it wanted, then I can imagine the hollowing of an entire planet would take nothing more than time.

And the metals to assemble machinery could be taken from the core.

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1 minute ago, daniel l. said:

If there was a society that was sufficiently automated as to just order the drone swarm to do whatever it wanted

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Just now, steve_v said:

I would assume that such a task as hollowing a planet would not take anything more than simple labor, it's not singularity mining after all. It's merely the process of cutting a hole in the crust and ordering trillions of tiny robots to go in and scoop out the interior like one serves a cantaloupe.

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Posted (edited)

11 minutes ago, daniel l. said:

A Dyson sphere according to the actual theory of Freeman Dyson is not a solid shell, rather a tightly knit swarm of spacecraft.

And to move a hollowed planet all you need a is a bigass EmDrive.

Bigass doesn't even cover it. The recent Eagleworks EM drive supposedly "produced" (you may be able to tell that I still think EM drives are a load of absolute rubbish) 1.2 mN per kW of energy supplied. Even assuming this is improved by a factor of 100 by the time you attach a huge EM drive to a hollow planet then we have 0.12 N per kW. To obtain an acceleration of an Earth mass planet of just 0.001 g needs roughly 6x1022 N which requires 5x1026 J to produce. So if you have an EM drive capable of moving a planet, you have already invented an energy source to power a planet killer.

Edited by Steel
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Just now, Steel said:

Bigass doesn't even cover it. The recent Eagleworks EM drive supposedly "produced" (you may be able to tell that I still think EM drives are a load of absolute rubbish) 1.2 mN per kW of energy supplied. Even assuming this is improved by a factor of 100 by the tie you attach a huge EM drive to a hollow planet then we have 0.12 N per kW. To obtain an acceleration of an Earth mass planet of just 0.001 g needs roughly 6x1022 N which requires 5x1026 J to produce. So if you have an EM drive capable of moving a planet, you have already invented an energy source to power a planet killer.

And thus every faction in the galaxy gained the power to build a fleet of death stars.

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2 minutes ago, daniel l. said:

I would assume that such a task as hollowing a planet would not take anything more than simple labor, it's not singularity mining after all. It's merely the process of cutting a hole in the crust and ordering trillions of tiny robots to go in and scoop out the interior like one serves a cantaloupe.

This would also need energy to break the gravitational binding of the planet. You seem to think at level on which you should not worry too much about realism. In my opinion planet vaporizing lasers would fit well in story which have planet carving drones, Dyson spheres, bigass EmDrives able to move planets etc. totally unrealistic technomagic.

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2 minutes ago, daniel l. said:

And thus every faction in the galaxy gained the power to build a fleet of death stars.

And here is a fundamental trap in SciFi.
If you need to move worlds, travel faster than light, or achieve some other gargantuan task, you suddenly find yourself in a situation where everyone can annihilate planets on a whim... Some mechanism to make the technology difficult to obtain must be invented, or the plot implodes.

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Just now, steve_v said:

And here is a fundamental trap in SciFi.
If you need to move worlds, travel faster than light, or achieve some other gargantuan task, you suddenly find yourself in a situation where everyone can annihilate planets on a whim... Some mechanism to make the technology difficult to obtain must be invented, or the plot implodes.

Now, my idea assumes that planet's have lost relevance as centers of population. And that they are only useful as massive ships. The majority of humanity lives in Dyson Sphere's/Swarms which can hold quintillions of people and be extremely difficult to destroy (Unless of course you somehow forced the explosion of the central star, which would be difficult if it was too small to go supernova naturally.)

Just now, Hannu2 said:

This would also need energy to break the gravitational binding of the planet. You seem to think at level on which you should not worry too much about realism. In my opinion planet vaporizing lasers would fit well in story which have planet carving drones, Dyson spheres, bigass EmDrives able to move planets etc. totally unrealistic technomagic.

Why not? Why wouldn't a thruster that works on small scale work in big? Just scale up everything, if they are merely taking out tiny chunks piece by piece over the course of many years, than I would assume it would not be too hard.