Water in Moon Rocks

[reynoldbot]

Hey, I just have a stupid question about moon rocks:

Since moon rocks are anhydrous, what would happen if you put one in a microwave? I've read that microwaves work by exciting the water molecules in whatever object is placed in them, so if moon rocks are anhydrous does that mean they would be unaffected?

Sorry if this is unrelated to Apollo. I guess it could be indirectly related to the HB claim that moon rocks are just earth rocks put in "radiation ovens", microwaves being the closest thing I can think of.

[Tanalia]

It's a popular misconception that microwave ovens operate at the resonant frequency of water (which is actually in the far infrared, 5-15 micron wavelength range). The fequency used (normally 2.45 GHz, or 12 cm wavelength) is simply absorbed by the food (or other material in general) in almost the same manner that normal light is; it just tends to penetrate further beyond the surface, on average, before being completely absorbed. The result is that the food tends to cook more-or-less evenly throughout rather than outside-in from normal heat conduction.

Most substances will absorb some of the microwaves and will thus warm up in a microwave oven. A substance which is relatively opaque to that frequency will absorb the energy near the surface, and heat up from the outside; the same as in a conventional oven.

Regarless of how you were to heat a rock, the water in Earth rock is chemically bound within the minerals. You would have to heat the rock beyond melting before the water would be released -- even lava and magma on Earth contain water.

[gwiz]

Going in over my head, I seem to remember reading somewhere that the water content alters (lowers?) the melting point of rock, so also altering the way in which the various constituents crystalise out as the molten rock cools. Presumably this is one of the ways geologists can measure how much water was present when the rocks formed.

[reynoldbot]

Thanks a bunch Tanalia for the great reply. It's strange that the "excite water molecules" basis is so widespread since by your explanation it has pretty much nothing to do with how microwaves work. Have any idea where that misconception came from?

Thanks both to you and gwiz for the info on water being chemically bound in rocks. I've heard it stated on this forum before that the only way to get the water out of a rock is to melt it, but I learn it better the more I read it. My father is a geologist but I never really knew too much about it. It gets ever more interesting the more I read about it on this forum.

One of the perks of being on this forum is all the things you learn just by reading some of these threads. I've gone from knowing the arguments and rebuttals of the Hoax theory to knowing the history and basic mechanics of apollo to learning a bit about the sciences affiliated with it. Thanks again!

[Tanalia]

The EM energy of the microwave will apply forces (equal and opposite) to the protons and electrons in the molecules. Since the charges are balanced in normal molecules, the net result is no linear acceleration of the molecules. Many molecules, though, have an asymmetric arrangement of those charges, more protons on one side of the center and matching electrons on the other -- a dipole (the electric equivalent of a tiny magnet). This applies a torque (twisting force) that tries to to line up the dipole with the electic field of the EM wave. As the wave continues, the field reverses and the dipole tries to realign to the opposite direction. The behaviour of the molecule is then something like a compass needle when a magnet is swung back and forth nearby.

Liquid dipole molecules are pretty free to rotate and can absorb a lot of energy, solid ones are more restrained and can only sort of rock back-and-forth in place, but still absorb some energy.

Water is one of the most well known dipole molecules, is present in all food, and is normally liquid, so it tends to get all the credit, even though there are thousands of different chemicals in food which react the same way. Except, of course, if you're heating just water .

Resonance is when an input force matches a natural frequency of the system, and causes the vibration to increase. Without some sort of damper to bleed off energy (such as a resistor in an electronic circuit), the vibration can buld out of control. Probably the most famous example of mechanical resonance failure is the first Tacoma Narrows Bridge.

The microwave situation is similar to a beach ball bobbing on ocean waves. Energy is being transferred, but it has nothing to do with resonance -- the natural frequency of a beach ball is probably a couple hundred Hz (just guessing, I don't have one handy to thump, nor an oscilloscope or similar device to analyze the sound , while the frequency of the ocean waves are on the order of 1/2 Hz.

[Tanalia]

Oh, and before anyone asks, yes, portable phones operating at 2.4 GHz (or pretty much any radio frequency) will heat up the molecules in your head! However, the energy level is so low that it's not a problem -- you receive more heat energy from light in a moderately lit room or outside on a cloudy day ;D

[reynoldbot]

Truly Interesting stuff, Tanalia. You know your resonating frequencies quite well! Thanks for the information.