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Moholaser

Why is there no "Science: Geology" category?
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Back in the 1960s, a project was begun to drill through the Earth's crust to the Mohoroviç discontinuity, marking the boundary between the crust and the mantle.

Had the project - known as Project Mohole - succeeded, it would have been immensely valuable. Its value, of course, would have lain in being able to say "we drilled through the Earth's crust!".

Sadly, Project Mohole fizzled out (though it did give birth to the science of dynamic positioning for drilling rigs). Other very deep holes (notably the Kola Superdeep Borehole) have been drilled, but none has got more than half way through the crust.

But now we have lasers and, as is well known, lasers make everything better. Proposed, therefore, is Project Moholaser. A high-power pulsed laser is simply pointed downwards, and is roofed over by a dome from which air can be evacuated. Each laser pulse will melt and vaporise a few millimetres of rock, which will be drawn out of the hole by the vacuum. With a few pulses per second (easily attainable), about a month should be enough to reach the mantle.

The depth attainable in this way is limited only by the Werther's Limit - which is slightly below the Mohoroviç discontinuity, and is the point at which rock becomes sufficiently toffee-like to flow more quickly than it can be vaporized by the laser.

MaxwellBuchanan, Oct 18 2018

Lava Wells Lava_20wells
Prior Art [8th of 7, Oct 18 2018]

http://home.earthli...et/~jimlux/lava.htm [hippo, Oct 18 2018]

http://www.madsci.o...015040902.Es.r.html [hippo, Oct 22 2018]

[link]






       Cool, but wouldn't this just promote a man-made volcano to form?   

       And?
MaxwellBuchanan, Oct 18 2018
  

       and... so where do we set this thing up?   

       Milton Keynes.
8th of 7, Oct 18 2018
  

       If the Earth's crust is 30km thick and you want to melt a hole of cross-sectional area 0.5m^2, then there's about 15000m^3 of rock to melt. If rock is about 3000kg/m^2, then this is 45,000,000kg of rock. Rock requires about 900kJ/kg to melt it (see link), so this is 40.5x10^9 kJ, or about 40TJ.

There are 2.5m seconds in a month, so this requires a continuous 16.2MW laser, assuming perfect efficiency at extracting the molten rock and no heat conduction to surrounding rock.
hippo, Oct 18 2018
  

       So, a little hobbyist-type laser - all pretty practical, then. Heat loss shouldn't be an issue due to the low thermal conductivity of rock, and besides as the hole gets deeper the surrounding strata get much hotter tending to help the process.
8th of 7, Oct 18 2018
  

       //wouldn't this just promote a man-made volcano to form?// I once proposed the creation of a small volcano for a public art installation. It was rejected, so it's still awaiting funding to proceed.
xenzag, Oct 18 2018
  

       That's probably related to the difference between the human perception of "small" and the geological reality.   

       Mud volcanoes can be on a modest scale, just a few metres across; on the other hand, many true volcanoes fall into the "really quite big" category.   

       You could try prodding Vesuvius with a stick and see if you can get it to start, although that might be unpopular with many in the vicinity.
8th of 7, Oct 18 2018
  

       //lasers make everything better//   

       Tell that to both of my eyes that now have plastic lenses because of lasers.   

       Bun for the idea though.
doctorremulac3, Oct 18 2018
  

       You’re not taking into account the Jelib Ab’iis coefficient, which was mentioned in a paper somewhere.
Ian Tindale, Oct 18 2018
  

       And the precise location of the Werther's limit usually requires a fudge factor.
DenholmRicshaw, Oct 18 2018
  

       //about 40TJ.// That's for a hole of 0.5m^2, or 5,000cm^2 I think even a 1cm^2 hole would qualify, taking the energy cost down by a factor of 5000. That means we're looking at a 3kW laser running non-stop for a month, and I think I could handle that (my lab draws about 10kW even when I'm not doing anything).   

       On the other hand, that's only the energy needed to *melt* the rock, whereas I need to vaporise it. So, probably double the energy bill. But it's still manageable.   

       I mean, seriously, why has nobody done this?
MaxwellBuchanan, Oct 19 2018
  

       If one of us thought it up... then odds are it was already tried by somebody fifty-plus years ago and classified.   

       The things taught are So far behind the things actually known it's like really not funny anymore.   

       You would need the earth to be air-tight too - no doing this through sand.
caspian, Oct 19 2018
  

       Substances are generally easier to boil (aka vaporise) at low pressure, but maybe not so much if you have to supply all the heat with a laser.
caspian, Oct 19 2018
  

       //The things taught are So far behind the things actually known it's like really not funny anymore.// I know - I was saying the very same thing to my android on the way to Mars yesterday.
MaxwellBuchanan, Oct 19 2018
  

       That's about where we could be by now.   

       // earth to be air-tight //   

       If the laser's configured to vitrify the sidewall, that won't be a problem.
8th of 7, Oct 19 2018
  

       [hippo]'s numbers don't account for beam divergence. I'm not sure what the divergence of such a high power laser would be, but the best laser pointers have a beam divergence of about 0.5mRad, so at 30km the beam diameter would have increased by about 15m. That's a substantial amount more rock to remove, so it would need substantially more power.
mitxela, Oct 19 2018
  

       Dynamic focus control.
8th of 7, Oct 19 2018
  

       Exactly.
MaxwellBuchanan, Oct 20 2018
  

       I think that in future generations, there’ll be more perceived value in establishing first exactly how crusty the Earth’s crust is. Quantifying crustiness is important in many ways, among which, one of them is to establish what kind of tooling to apply to the crust, and the other of which is to come to a consensual concurrence of whether a crust should be penetrated, eradicated or just laughed at. In other words, we need to design a drill that decides what it should be doing in life in the first place.
Ian Tindale, Oct 20 2018
  

       Condensation of the vaporised rock onto the side of the borehole would be a continuous issue.
AusCan531, Oct 20 2018
  

       //Condensation of the vaporised rock// It would. Howevertheless, if the rock condenses it will impart energy of condensation to the walls of the hole, making it easier for the next laser pulse to re-vaporise the material.
MaxwellBuchanan, Oct 20 2018
  

       Depends on the hysteresis phase indent.
Ian Tindale, Oct 20 2018
  

       I don't think so. Ultimately, it takes X amount of energy to vaporise Y amount of rock.
MaxwellBuchanan, Oct 20 2018
  

       X amount, eh?
Ian Tindale, Oct 20 2018
  

       Thought of something similar earlier:   

       put laser hole driller on planetary explorers, like mars explorer, to sample geology. I think you could dump something like a plurality (dozens?) of those cone-weighted payloads or gombochs that was just a solar panel and a laser rock drill and some sensors.
beanangel, Oct 20 2018
  

       //that's only the energy needed to *melt* the rock, whereas I need to vaporise it. So, probably double the energy bill. But it's still manageable// - indeed, I couldn't find the data last time I looked, but I've got a better source now (see link). The link says "We are not likely to find a value for latent heat of vaporization of quartz at its boiling point. The best option is to assume that it is much smaller than the heat input needed to raise the temperature.". However the per kg energy consumption this analysis comes up with is about 2775kJ/kg, as opposed to the 900kJ/kg I came up with before. So, you'll need about a 50MW continuous laser beam for a month.
hippo, Oct 22 2018
  

       //I mean, seriously, why has nobody done this?//   

       I think I saw a documentary about this - a team of scientists built a sort of thunderbird four but with lasers on the front, so they could go down inside the Earth's core in and futtle about inside.
Loris, Oct 22 2018
  

       Did the project leader have a fluffy white cat with a diamond-studded collar, by any chance ?
8th of 7, Oct 22 2018
  

       //a documentary about this - a team of scientists built//   

       By "documentary" do you mean "film"? Alternatively, by "built" do you mean "imagined"? I'm fairly certain that nobody has actually futtled in the Earth's core, even though futtling would certainly be useful.
MaxwellBuchanan, Oct 22 2018
  

       "The Core" it's called. You could probably research it on netflix or DVD.   

       With your method, I would predict that lasing from the top would reach a maximum depth where inwelling of semi-molten rock would match beam energy. At best. Because you're also shooting through the vapour on its way out, which probably incurs a lot of heat transfer to the sides of the hole, leading to further melting and enlargement. If you don't get stymied by water incursion way before then.   

       As you know I favour the strategy involving a nuke and a week's worth of all iron-foundry production.
Loris, Oct 26 2018
  

       I dunno, [Loris]. It's perfectly possible to drill very high aspect ratio holes in most materials with a laser. So, the question is, what changes as the hole gets much, much deeper?   

       Well, the sides of the hole won't change as the hole gets deeper, so that's not a problem. However, the vaporised material has further to go to get out of the hole (and, if it doesn't get out, it will indeed attenuate the beam). Hence the cunning use of vacuum.   

       Now, admittedly, when the hole is deep enough, not all the vapour from one pulse will have escaped the hole before the next pulse happens so, depending on the pulse rate, you'll always have a finite amount of rock vapour in the beam path. Howevertheless, vaporised rock is probably not going to be as opaque as solid rock. And you could always increase the interval between pulses as the hole gets deeper, to give more time for rock vapour to escape.   

       So, yes, you'll lose some energy to absorption along the beam, but I still say it's worth a shot.   

       At the very least, someone ought to make a pencil-wide hole through the bottom of Everest as a trial project.
MaxwellBuchanan, Oct 26 2018
  
      
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