A Mission to the Earth’s Core

Published in the December-2003 issue of Analog Science Fiction & Fact Magazine ^ | 06/22/2003 | by John G. Cramer

[Doctor Stochastic]

Iron density 7874kg/m^3

Volume 30m sphere (assuming 30m is diameter): Pi/6*(30m)^3 gives Pi*4500m^3 volume.

Mass = Pi*4500m^3*7874kg/m^3 (using 355/113 for Pi) = 111,316,061kg.

This is about the weight of the Battleship Missouri (which is bigger, but hollow.)

[Doctor Stochastic]

Another reason for abandoning the MOHOLE was that much of the stuff to be studied is just lying on the ground in northern California (actually, it is the ground.) Much of that area is sea-crust as opposed to continental crust.

[Flightdeck]

that book was awful.

[HuntsvilleTxVeteran]

The moho area was selected because it was one of the shortest paths through the crust to the mantle.

So you think the liquid mantle under the stress of the crust and the heat is the same as a lava flow?

[Doctor Stochastic]

So you think the liquid mantle under the stress of the crust and the heat is the same as a lava flow?

No. I never said anything like that.

[Oberon]

Pardon me, but it appears that you've computed the mass of a sphere with a 30m radius, not a 30m diameter...unless perhaps I'm missing something? Volume is 4/3rds pi*(r^3), yes?

[SlowBoat407]

Looks to me like they would just be drilling a hole for another volcano.

Amen to that! It's bad enough when we get weak spots in the crust allowing the magma to punch through. Now we're talking about an engraved invite for the stuff?

[SlowBoat407]

Are you talking about Schuler oscillation? Sounds familiar.

[HuntsvilleTxVeteran]

"Another reason for abandoning the MOHOLE was that much of the stuff to be studied is just lying on the ground in northern California (actually, it is the ground.) Much of that area is sea-crust as opposed to continental crust."

The mohole project was not about the crust it was about going through the crust to sample the mantle.

[Fresh Wind]

[Doctor Stochastic]

That's why I have Pi/6 rather than 4*Pi/3.

[Doctor Stochastic]

The geologists I knew told me that lots of the MOHOLE work was for looking at oceanic crust. Of course, going to the mantle would be different. Now that Haliburton has absorbed Brown&Root and there's another Texan in the White House, maybe they'll try again.

[Oberon]

That would work okay if you didn't have to cube the radius. Your result is off by a factor of 8 (2 cubed), as far as I can tell.

[Physicist]

Physicist, what do you think? Zero gravity inside a massive hollow sphere?

Zero gravity from the sphere itself, yes. Put a black hole (or a planet, or a star, or a crouton, or...) somewhere, inside or outside of the sphere, and you'll feel the gravitational field from that, but the field from the sphere itself will be zero inside.

Consider any arbitrary chunk of the sphere. It subtends some patch of solid angle with respect to you. The gravitational pull from that chunk is opposed by the pull of a similarly-shaped chunk on the opposite side of you. Get this: the size (and therefore the mass) of each chunk will grow as the square of its distance from you. Its gravitational pull will fall off as the square of its distance from you. Those two factors cancel, thus the pull from each piece is equal and opposite. That zero-pull argument works for any arbitrary piece in any arbitrary direction. Integrate that zero over the entire sphere, and you get zero.

[Physicist]

Shows what I get for responding without reading the thread. <g>

[RadioAstronomer]

bttt

[johnnycap]

Sounds like a great idea. Let's blow up the planet for sh*ts and grins.

[Oberon]

Very succinctly put...much better than my explanation in Post 52.

[Tarpaulin]

Thanks.

[HuntsvilleTxVeteran]

The geophysicists with whom I worked with knew the purpose of the mohole and the moho area.

During the time of the mohole project, we also set up a vibroseis crew in New Mexico that used both a long sweep and a very long listening time in order to try to get some more data on the mantle.