Misleading mineral may have resulted in overestimation of water in moon

Researchers have suggested that the amount of water present in the moon may have been overestimated by scientists studying the mineral apatite.

Jeremy Boyce of the UCLA Department of Earth, Planetary and Space Sciences and his colleagues created a computer model to accurately predict how apatite would have crystallized from cooling bodies of lunar magma early in the moon's history.

Their simulations revealed that the unusually hydrogen-rich apatite crystals observed in many lunar rock samples may not have formed within a water-rich environment, as was originally expected.

This discovery has overturned the long-held assumption that the hydrogen in apatite is a good indicator of overall lunar water content.

Boyce, who is an adjunct assistant professor in the UCLA College of Letters and Science, said that their new results show that there is not as much water in lunar magma as apatite would have them believe.

Boyce believes the high water content within lunar apatite results from a quirk in the crystallization process rather than a water-rich lunar environment. When water is present as molten rock cools, apatite can form by incorporating hydrogen atoms into its crystal structure. However, hydrogen will be included in the newly crystallizing mineral only if apatite's preferred building blocks, fluorine and chlorine, have been mostly exhausted.

Therefore, when fluorine and chlorine become depleted, a cooling body of magma will shift from forming hydrogen-poor apatite to forming hydrogen-rich apatite, with the latter not accurately reflecting the original water content in the magma.

The research was has been published online in the journal Science.