Reasons for Ice

Volitiles accumulate and may be stable over geologic time:

• Steady Sources

  • Silicates Reduced by H in Solar Wind
  • Sunlight Desorbs Regolith H2O
  • Micrometeoroids
  • Gradual Degassing from the Interior

• Comet Impacts

  • Comets are > 70% Water
  • Comet Mass ~ 7 x 1013 Kg
  • Time Between Impact ~ 13 million years

• Loss Mechanisms

  • Sublimation (& ionization and loss to space)
  • Meteoroid Impact
  • Solar Wind/Radiation
  • H Lya Flux from Interstellar Medium

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