Volatile content of lunar volcanic glasses and the presence of water in the Moon’s interior

Lunar glass: Reflections on a watery Moon Although it has been suggested — controversially — that water ice might be found in the permanently shadowed deep polar craters on the Moon, the bulk Moon is thought to have lost virtually all of the highly volatile elements, including water, long ago during the catastrophic heating events that led to its formation. Hydrogen, as the lightest element, is thought to have been completely lost. Saal et al . used the latest secondary ion mass spectrometry techniques to derive improved limits on the indigenous volatile (CO2, H2O, F, S, Cl) contents of the most primitive basalts in the Moon, the lunar volcanic glasses. Their best estimate of the pre-eruptive water content is 745 p.p.m., with 260 p.p.m. as a minimum. This suggests that the bulk Moon is not entirely depleted in water and other highly volatile elements. A report providing improved limits on the indigenous volatile contents of the most primitive basalts in the Moon, the lunar volcanic glasses. The best estimate of the pre-eruptive water content of the lunar volcanic glasses is 745 p.p.m. water, with a minimum of 260 p.p.m., indicating that the bulk Moon might not be entirely depleted in highly volatile elements, including water. The Moon is generally thought to have formed and evolved through a single or a series of catastrophic heating events 1 , during which most of the highly volatile elements were lost. Hydrogen, being the lightest element, is believed to have been completely lost during this period 2 . Here we make use of considerable advances in secondary ion mass spectrometry 3 to obtain improved limits on the indigenous volatile (CO 2 , H 2 O, F, S and Cl) contents of the most primitive basalts in the Moon—the lunar volcanic glasses. Although the pre-eruptive water content of the lunar volcanic glasses cannot be precisely constrained, numerical modelling of diffusive degassing of the very-low-Ti glasses provides a best estimate of 745 p.p.m. water, with a minimum of 260 p.p.m. at the 95 per cent confidence level. Our results indicate that, contrary to prevailing ideas, the bulk Moon might not be entirely depleted in highly volatile elements, including water. Thus, the presence of water must be considered in models constraining the Moon’s formation and its thermal and chemical evolution.