Imagine we have a machine that can consume celestial bodies, breaking them down into component elements and storing them in big bins somewhere. If we fed that machine a moon, what would wind up in those bins?


  • Earth's moon.
  • We do not concern ourselves with the planet the moon is orbiting. It is likely next on the menu anyway.
  • How the machine functions is open to speculation, but not part of the question.
  • 1
    $\begingroup$ The moon... do you mean what is the moon made of? $\endgroup$ – kaine Oct 24 '14 at 14:01
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    $\begingroup$ @kaine: It's made of green cheese, of course. $\endgroup$ – celtschk Oct 24 '14 at 17:17
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    $\begingroup$ This Star Trek episode explored the idea of such a device as an automated war machine. $\endgroup$ – Paul Oct 24 '14 at 19:42
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    $\begingroup$ @Paul Most of the questions on this SE will get us decent Star Trek Episodes. $\endgroup$ – Danny Reagan Oct 24 '14 at 19:42
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    $\begingroup$ "What do we get if we eat the moon?" - A very bad stomach ache, and a painful bowel movement. $\endgroup$ – Caleb Hines Oct 25 '14 at 0:33

The volume of the moon is $2.1958*10^{10} \,\rm km^3$ (0.020 Earths), and its mass is $7.3477*10^{22} \,\rm kg$ (0.012 Earths).

As is to be expected, we know more about the surface and the atmosphere (yes, there is one) than we do about the mantle or the core.

The Core

The composition of the lunar core is not well constrained, but most believe that it is composed of metallic iron alloyed with a small amount of sulfur and nickel.


The largest portion of the Moon is the mantle. This is the layer between the crust (the part we see) and the inner core. The composition of the mantle is similar to that of the Earth, but the Moon may contain a higher percentage of iron.

Surface Crust Composition

Scientists have samples of the lunar crust and take measurements of properties of the Moon's surface. The crust consists of 43% oxygen, 20% silicon, 19% magnesium, 10% iron, 3% calcium, 3% aluminum, and trace amounts of other elements including 0.42% chromium, 0.18% titanium, 0.12% manganese, and smaller amounts of uranium, thorium, potassium, hydrogen and other elements.

Lunar Atmosphere

Total mass of atmosphere: ~25,000 kg Abundance at surface: 2 x 105 particles/cm3

Estimated Composition (particles per cubic cm):

  • Helium 4 (4He) - 40,000
  • Neon 20 (20Ne) - 40,000
  • Hydrogen (H2) - 35,000
  • Argon 40 (40Ar) - 30,000
  • Neon 22 (22Ne) - 5,000
  • Argon 36 (36Ar) - 2,000
  • Methane - 1000
  • Ammonia - 1000
  • Carbon Dioxide (CO2) - 1000
  • Trace Oxygen (O+), Aluminum (Al+), Silicon (Si+) Possible Phosphorus (P+), Sodium (Na+), Magnesium (Mg+)

Composition of the tenuous lunar atmosphere is poorly known and variable, these are estimates of the upper limits of the nighttime ambient atmosphere composition. Daytime levels were difficult to measure due to heating and outgassing of Apollo surface experiments.

Moon Cross Section From Wikipedia Commons

Note: Thanks to Kromey for the MathJaX.

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  • $\begingroup$ And you can do the math yourself to work out how much of each! [grumpily shakes fist]. :-) $\endgroup$ – Mourdos Oct 24 '14 at 14:25
  • $\begingroup$ @Mourdos Any time. Just learning it myself, and it's a lot of fun, so I'll take any excuse to put it anywhere! :) $\endgroup$ – Kromey Oct 24 '14 at 15:58
  • $\begingroup$ In school (late 90's) my earth and atmosphere professor was very insistent that the mantle of the moon would contain significantly lower concentrations of iron. Interesting to know this theory has changed. $\endgroup$ – Twelfth Oct 24 '14 at 23:17

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