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Falling to Earth's Core in a Big Blob of Iron
Colin Douglas Howell writes "Um...wow. I found this idea via the BBC, (see also the Nature article), but it's really worth reading the annotated paper on the subject. (Gotta love the title.) Basically, you drill a hole in the crust, blast a big crack in it, inject a huge mass of molten iron with a little probe floating inside (made out of material which won't melt or dissolve in the iron), and let the iron mass sink to the core by gravity, carrying the probe with it. (The initial crack grows downward as the iron sinks.) As the probe falls, it sends data back using seismic signals that can be picked up with a gravitational wave observatory like LIGO, but coupled to the ground. Of course, there are enormous problems with the whole thing, but it's still cool to read about. To me, the idea is even neater because it was dreamed up by Dave Stevenson, one of my old professors (and one of the best professors I've ever had). I hope he doesn't mind being Slashdotted. :-)"
I'm no geologists, but based on what I learned in school (no doudt out-dated by now), the mantle is molten rock and probably gets hotter as you near the core. So what is stopping this molten iron from dispersing into the molten rock in the mantle?
They are called volcanos? Why not just send a probe down a volcano and call it a day.
Here's a question, though. Could someone design parabolic shaped tunnels between destinations for transportation?
Suppose one built a tunnel between New York and Los Angeles that is parabolic. Then, design it with some kind maglev system to reduce friction. Could you then send specially designed cars through these tunnels with a minimum of energy expended?
Maybe you could impart the the car with enough velocity at the beginning so it comes to a gentle stop at the end.
Has someone already done this in Science Fiction? Has anyone ever tried it in reality?
However, I think the pesky rotation problem will do you in anyways. Linear velocity at the equator exceeds Mach 1.5; at the exact core it's essentially zero. Dropping down a hole does not magically rid you of that sideways momentum, so you will probably be getting a stone wedgie long before you even hit the mantle. You'd have to stick a rail guide along the side which, since frictionless unobtainium isn't yet in mass production and Hotblack Desiato has first dibs on the stuff anyway, would cause you to lose some of that precious inertia on the way down, thus requiring that you expend power getting yourself up the last bit.
Assuming that I were particularly interested in going to China in the first place, I'll just take a cruise, thank you very much.
Dyolf Knip
Interestingly, any frictionless tunnel that you bore from one point on the earth to any other point will work this way. It doesn't have to go through the center, and it doesn't have to be parabolic. In theory, you could bore a tunnel from your house to your workplace down the street and travel there with no energy expenditure. Transit time is another issue; any straight tunnel will take the same time no matter what the distance (I think it's about 90 minutes, although I'd have to dig out my orbital mechanics notes to verify that), and you can get better transit times with different trajectories. This is all assuming a uniform, spherical earth, no friction or drag, etc.
Step 1: Draw up plans for frictionless tunnel
Step 2: ???
Step 3: Profit!
Firstly the probe will have to have all its parts be heat resistant, else should have an internal cooling method, and not just one of those Duron fans. And then the probes net density should be the same as the molten iron, so it doesnt float over it and touch the lava. Better yet it should have a way to adjust its own density, maybe eject some ballasts. Since most electronics are less dense than iron, to balance it, the probe should have material that has more density. I wonder if lead would do, or should we try Uranium.
I think the biggest problem will be the earths crust. Where can we find or drill a hole large enough vertically straight?? Hawaii?? Mount Fuji should be a better place but do we really want to drill a hole in that given its history?
And finally the idea that most of the space under the crust is molten mantle is still just a theory. Maybe 100 meters down the iron will just sit on another mass of rock that just happens to be there. And I dont know how will it find and go through cracks. If like water its allowed to drain, it will spread thin enough to damage the probe, so LOTS and LOTS of molten iron should be used on a vertical shaft like mount fuji.
I think radio waves of the right freq can travel within the mantle, so we could have large satellite dishes pointed into the ground. Heck we could even send bombs to China. Designer earthquakes!
"Give orange me give eat orange me eat orange give me eat orange give me you." -Nim Chimpsky
Oh I wouldn't worry about that. After the first few miles, the temperature of the surrounding rock would be enough to keep the iron molten. Ever see pictures of lava moving through water? Kinda like that, only instead of being chilled on the outside and kept warm from the inside, it's the other way around.
Besides, if your probe's cooling system is good enough to actually chill several million tons of iron whilest encased in liquid silicate rocks, you could really dispense with the whole molten iron thing and just make the thing dense and massive enough to fall of its own accord and provide it with a heat source to keep the outside piping hot while your magical freon unit maintains room temperature on the inside.
Dyolf Knip
What kind of information about its surroundings could the probe pick up from inside all that molten iron?
/. If the government wants us to respect the law, it should set a better example.
Wow, 108 comments and I have yet to find one that discusses the proposition in any detail. (maybe all those fluid dynamics equations are as foreign to other slashdotters as they are to me :-) At any rate, I just finished reading the annotated paper, and I've got a few comments and questions:
1) Why, instead of using all this iron buisiness, don't we simply use a radioactive ball of goo? This would mean that the whole blob could be a lot smaller as you wouldn't have to worry about maintaining the heat - the radioactivity can do that for you! As well, given that melting point increases proportionally to pressure, and that the pressure in near the earth's core is extremely high, you don't have to worry about getting the iron hot enough to not worry about that. The guy writing the paper does mention the possibility of using nuclear, but he doesn't give any good reason why not.
2) Nice quote - "The correct application of this energy to open up a crack and the technological challenge of emplacing the iron should be much less challenging than the manhattan project." He does realize how difficult the manhatten project was, doesn't he?
3) He mentions that the hole would not completely close up behind the probe (NB - this would not cause a volcano, for reasons he points out, mostly due to tube size and geometry). Why is this the case? does some of the matter get combusted into a gas and escape out the chimney? or is there something else here that makes this not violate the conservation of matter? On another thought, would it be possible to lower a second probe down this chimney?!
4) The sensor package he discusses would look for temperature, pressure, trace + major elements, and electrical conductivity, etc. I can understand the pressure bit, but wouldn't the temperature and element sensors only be sensing the iron casing that the probe was injected with? unless he has some other method of sensing these things at some distance away from the probe I don't see how this is possible (maybe trace elements mixed with iron on the way down, but the experimental error in this would be huge). On another note, using the nuclear probe proposal in point 1, could it be possible to moderate the nuclear reaction and thus stop the probe for a bit, do some sensoring (whatever that may be, and I know I made that word up) and geology, then start up again? Also, this would be valuable for point 5...
5) He mentions that we don't know much about working with seismic waves. Wouldn't all this iron buisiness and the fact that its fluid potentially cause problems with the seismic signal? (like distortion, etc) Given that we haven't done much encoding/modulating, and transmitting of data using seismic waves, it might be a good idea to perfect this first. The only other option I could see would be emitting a constant signal and watching how it varies as the probe descends, and then extrapolating this for data (of course, then you don't get the juicy data at the probe itself).
There's more I could think of, but I do want to get this out, and I've got other things I should be doing. All the same, the article was an interesting read and stimulated the brain cells fairly well, even if it is completely impossible!
Can any engineers in the audience explain to me how this trick works? I have an... intuitive grasp of it, but I don't understand the specifics.
Yours, YLFI.
"Liquids are incompressible."
Yes, they are. It's just negligible in most real-world situations. Going miles under molten rock doesn't fall into the "real-world situation" category, though.
But even if this probe were going down in a blob of uncompressable molten unobtanium, Pascal still says that the pressure within the blob is the same as the pressure outside the blob.
"Furthermore, if you made the probe a solid sphere, it'd also be pretty much indestructible."
Ignoring the problem of making sure it really is solid (unless it's truly homogeneous, you're going to have gaps) and the fact that even a solid will compress if exposed to enough pressure, how is it going to produce those "seismic waves" it's supposed to use to communicate to the surface?
"While that may not be terribly useful, it would at least prove you'd be able to send something down there."
How, praytell, will you demonstrate that it really did survive the descent? Go down after it and retrieve it?
Late 70s early 80s there was two extremely dangerous tests: 50 MT underwater by France in Pacific and 100+ MT underground by Soviets on New Zemlya. In second case, despte the fact that underground there was just a limited amount of water, the outcome was much greater than predicted. The shock wave did hit towns in North Russin in thousands of kilometers. The estimtaed energy after all measurements exceeded the originally calculated energey on more than 20 % - that's possible ony b/c the water underground has been involved in the fusion.
So, if they will make too intensive explosion than it's a big chance that they will miss something and trigger something they would not have planned originally. The outcome may include global cracks in the tektonic platforms and can be very catastrophic.
So, please, no more nuke/fusion exploisions - better invest money, resources and efforts into interplanetary communications: I want my vacations in Europe. You got it right - *THAT* Europe :)
Less is more !
Where is the weakest area in a crack? The endpoints. So any force directed on the endpoints can lead to catastrophic failure (makes the crack wider).
Now what's the weakest part of a circle?
Your argument is tantamount to the early arguments that a nuclear explosion would ignite the atmosphere. There's a small possiblity that some fusion would occur in surrounding water due to the shock wave from the explosion (heat and pressure + neutron flux); but, heat, pressure and radiation flux fall off as r^-2; so, there are natural limits on how far the effect could occur.
There's no reason (physics and engineering) which would limit the maximum size of a nuclear weapon. The sun is a naturally occuring, self-sustaining nuclear explosion...
The real reason for limiting the size of bombs is the insanity of it (if there is ANY sanity to using nuclear weapons) -- a bomb of 100 - 150 MTons would yeild a crater approaching 10 miles with an area destroyed by the blast in the 100's of miles radius. That hasn't begun to factor in the area affected by direct and indirect (fallout) radiation.
Why would you ever need anything even that big?