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In situ availability:
Atomic number: 18
Atomic mass: 39.948
group: 18
period: 3
normal phase: Gas
series: Noble gases
density: 1.784 g/L
melting point: 83.80K,
boiling point: 87.30K,
Cl ← Ar → K
Atomic radius (pm): 71
Bohr radius (pm): 71
Covalent radius (pm): 97
Van der Waals radius (pm): 188
ionic radius (pm): -
1st ion potential (eV): 15.76
Electron Configuration
2s2 2p6
3s2 3p6
Electrons Per Shell
2, 8, 8
Electron Affinity: Unstable anion
Oxidation states: -
Magnetism: Nonmagnetic
Crystal structure: Face centered cubic

Argon is a Noble gas in group 18. It has a Face centered cubic crystalline structure. This element has 3 stable isotopes: 36, 38, and 40.

Most of the volatiles have been deposited in the top layers of the Moon's surface by the solar wind over geologic time. A notable exception to this is Argon. The concentration of Argon in lunar soil is much higher than found in the solar wind, so must come from a different source. Especially, the isotope Argon-40. It is presently believed that the Argon-40 comes from radioactive decay of Potassium-40 deep within the lunar mantle or core, and that the Argon-40 seeps out to the surface via fissures. This lunar outgassing continues today. This vented Argon enters the lunar atmosphere; then the Argon is implanted into the regolith by interactions with ions from the solar wind.

Public domain info obtained from NASA:

Moon Fact Sheet

Lunar Atmosphere 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

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