Removing a Planetary Atmosphere

[Caiaphas]

So this is kinda migrated from a discussion over on Spacebattles.com regarding a scene in someone's story where Earth's atmosphere has been blasted away but the surface isn't still molten-hot after a few millennia.

The question I'm having is whether a. what kind of weaponry would you need to transfer enough energy to the atmosphere that a significant amount of it is kicked out with escape velocity, b. how much energy would this weaponry reasonably deliver to the planet's surface, and c. given that amount of energy, would the surface rock melt and if it did how long would it take to cool?

I'm thinking that the best way to carry it out would be with mass bombardment with explosives (antimatter, conventional thermonukes, what-have-you) detonated with airbursts. I'm assuming that thermal effects would get at least some of the gas moving at escape velocity, and most of the energy would be directed away from the ground.

Thoughts? Help?

[Sea Skimmer]

Maybe lasers fired at high grazing angles such that they don't strike the surface at all could do this, but that would be amazingly slow and deliberate.

Large air bursts would direct plenty of energy into the ground and be inefficient at ejecting anything, they might well make the heating problem even worse in some respects as a penetrating ground burst would also eject large amounts of surface mass, helping cool the impact area. On an earth like planet over 90% of the air mass is below 35,000ft and you already need very large blasts to have any chance of ejecting material past escape velocity. This is not a realistic goal for conventional or nuclear arms. I'd think more in context of how a planet might be cooled back down at that point, such as being subject to large scale ice comet impacts or such.

[Simon_Jester]

Hm.

About the only thing I can think of is 'attack by an enemy with large tractor beams and a lot of time to play with."

[Jub]

What if you got the math just right and used some sort of towed planet to siphon off the atmosphere? Would it even be possible to have a mass large and close enough to suck off the atmosphere, but small and far enough not to crash into the planet?

[madd0ct0r]

That was my first thought, but you would always knock the planet out of orbit around the sun.

are you allowed to manipulate gravity / have wormholes within the atmosphere?

[SpottedKitty]

The only thing that comes to mind is, not explosives, but something of a similar scale as the speculated planetoid impact that created the Moon — either one big sub-Mars-size smash or a bunch of large-asteroid smaller ones. As long as you don't overdo it, the impact shock should blast the atmosphere away nicely without pumping too much heat into the planet itself. If you do overdo it, the surface might take millions of years to cool down below boiling hot. For this to work, though, you'd need someone capable of setting up a Footfall (as in the Niven/Pournelle story) on a very large scale.

[Broomstick]

Or you could shut down the planet's magnetic field and let the solar wind do the job for you... of course, that would take a LONG time...

[Elheru Aran]

If nothing else, Spaceballs has *exactly* what is called for. Summon the Mega-Maid!

[Zaune]

Or you could shut down the planet's magnetic field and let the solar wind do the job for you... of course, that would take a LONG time...

Still, everyone dying of radiation burns instead of asphyxiation would accomplish the implied objective of "fuck those guys and the whole biosphere they're standing in." (Spacebattlers are not a subtle bunch.)

[SCRawl]

If nothing else, Spaceballs has *exactly* what is called for. Summon the Mega-Maid!

Needless to say, this is impossible. The idea of sucking away a planet's atmosphere when it's in regular contact with the best vacuum you can get is ridiculous. Ludicrous, you might say. Now, if our antagonists were allowed to set up pumping stations on or near the surface, each with *really* long tubes pointed straight up, you could blow out the atmosphere if you had enough time.

[madd0ct0r]

Oh, I'm an idiot.

Step 1 - build enormous solar shield out of many indepently moveable mirrors
Step 2 - use said sheild to focus sunlight and happiness on anything the planet tries to use to stop it blocking sunlight to you
Step 3 - wait for atmosphere to liquify/freeze out
Step 4 - bulldozers + space elevator / big gun, fire atmosphere towards other planet.

[Caiaphas]

Or you could shut down the planet's magnetic field and let the solar wind do the job for you... of course, that would take a LONG time...

...wouldn't you need to drill down to the core and somehow stop its rotation in order to stop the magnetic field? Forgive me, but it's been a really long time since I've studied geology and geophysics.

[Broomstick]

Haven't a fucking clue how you would do it, personally, but a lack of magnetic field (at least, a lack of a planet-spanning one) + solar wind is one theory on why Mars has such a spare atmosphere.

[Rossum]

Oh, I'm an idiot.

Step 1 - build enormous solar shield out of many indepently moveable mirrors
Step 2 - use said sheild to focus sunlight and happiness on anything the planet tries to use to stop it blocking sunlight to you
Step 3 - wait for atmosphere to liquify/freeze out
Step 4 - bulldozers + space elevator / big gun, fire atmosphere towards other planet.

Hmm... if we're allowed to use massive industry to remove the atmosphere, what about creating something to directly turn the atmospheric gasses into a solid? Something like this crystal that was invented to store oxygen.

Get a crystal or something that absorbs oxygen or nitrogen, or whatever, then use massive sci-fi tech to mass produce it (either manufacturing it on nearby asteroid belts, or on the planet itself using self-replicating machines). Place the material in some kind of mass-producable device and use them to steal the atmosphere. The result would be something like a several billion little ping-pong balls that can each suck in massive amounts of a specific gas. You've got some that suck in all the oxygen, some that suck in all the nitrogen, etc.

Do this enough and after a while the surface of the planet is covered in possible miles of lots of little canisters that soaked up all the air. These then get loaded up and shipped into space or whatever.

Or, it could be something like Tiberium from Commmand and Conquer, an invasive self-replicating crystal thing that also happens to soak up all the oxygen, nitrogen, and stuff from the atmosphere and converts it to a solid material.

[Simon_Jester]

What if you got the math just right and used some sort of towed planet to siphon off the atmosphere? Would it even be possible to have a mass large and close enough to suck off the atmosphere, but small and far enough not to crash into the planet?

It would be both much less work, and far more practical, to do it with very large numbers of individually smaller masses.

Compare this idea to proposals for thinning out the Venusian atmosphere as part of plans to terraform it.

[Napoleon the Clown]

Hitting Earth with a gamma-ray burst at sufficiently close range would be enough to strip off enough atmosphere (particularly the bits that protect us from the worst of solar radiation). Sufficiently close being a few hundred parsecs. According to Phil Plait 100 light years would set the entire goddamn (he doesn't use the word "goddamn") planet on fire. So there are things that could get rid of the atmosphere, but they involve enormous stars exploding, neutron stars merging, or maybe even black holes merging. Poking about online, the energy release of a "typical" long-duration GRB is the same amount of energy that would be released if the 1/2000th of the sun were converted directly to radiation.

So basically, nothing any society could bring to bear on a planet, but astronomical events could pull it off. That or find a way to turn off the magnetosphere, like Broomstick suggested. That would take longer, but it would be pretty damned effective in the long run.

[Vejut]

So, somebody check my math here, all number from wiki--
Atmospheric mass is 5.15x1018kg
escape velocity from the surface of earth is 11.2 km/s.
So the kinetic energy required to remove earths atmosphere, assuming it all started at the surface, would then just be escape velocity squared, times half the mass, which if I'm doing it right, is 3.2x1026J.

Originally, I was thinking I could take the earth's mass, and estimate a specific heat capacity of about 1 kJ/kg-K (probably high by about 10%), and get about a 19K rise in temperature (and an assumed efficiency of heat transfer of whatever blew off the atmosphere of 50%), which seems...very small and dealable. I'm thinking the problem is I'm assuming the heat heats the whole planet, not just the crust. Any way to estimate that? Basically, trying to figure out a blackbody temperature , so I can then figure out just how much heat is radiated per unit time, and then from there how long cooling would take. Though really...hrm. What if I just used the temperature of molten lava, and assumed it went all the way through the crust? Is this even a productive way to back of the envelope estimate the cooling time involved for Caiaphas' scenario?

[Borgholio]

...wouldn't you need to drill down to the core and somehow stop its rotation in order to stop the magnetic field? Forgive me, but it's been a really long time since I've studied geology and geophysics.

Sure. Just create a drilling submarine made of unobtainium, plant some nukes in the mantle, and set them off.

[Purple]

Is there any way that would acomplish said objective without 1) taking an unreasonable amount of time and 2) killing the people of the planet in the process so that they can't choke without an atmosphere?

[Borgholio]

You want to remove a planet's atmosphere without killing them so...they can suffocate instead?

[Pinjar]

You want to remove a planet's atmosphere without killing them so...they can suffocate instead?

Something like this seems insanely impractical so could be being done due to the wider political situation or for propaganda purposes. If you are evil then why not? Perhaps you even want to vacuum dry the people so you can sell their remains.

Edit: Not "you" but the hypothetical evil.

[Borgholio]

There's evil and then there's stupid. The best way to terrify someone is not to expend a great deal of resources to do something (relatively) simple, the best way is to easily and casually swat an entire world from existence without a second thought. To know that someone is coming for you that can have everything you know obliterated at the blink of an eye will instill more dread than the impression that it takes them a shit-ton of time and resources to perform the same task.

[Purple]

You want to remove a planet's atmosphere without killing them so...they can suffocate instead?

You know, I could write a complicated and elaborate explanation. But frankly I think that we'd all be better served with a simple YES.

[Elheru Aran]

In your fucked-up little world, unless you have control over the planet's magnetic field, it would probably be cheaper to just pack the population aboard massive spaceships, lift them off into orbit and simply expose them to vacuum. Or you could toss a few rocks at the planet. Trying to kill everybody by sucking away the atmosphere would be preposterously silly.

[Purple]

Yea, I know. It'd be like a tornado of joy. Only instead of joy it'd be death. And instead of a tornado it'd be meeee!