Water in the Solar System

Diffusivity and solubility of water in lunar basalt 

When lunar samples returned by the Apollo missions were first analyzed, they were found to be strongly depleted in volatile elements (e.g., Na, K, F, Cl, and S) compared to the Earth. In particular, no water was detected in the lunar samples. These findings were consistent with the prevailing hypothesis for the formation of the Moon, the so-called 'giant impact' hypothesis, which proposed that the Moon accreted from material ejected during an impact between the Earth and a Mars-sized body called Theia. Models of this giant impact event predict catastrophic heating and melting of the material that accreted to form the Moon, which would likely boil off the highly volatile components, including water. 

The detection of volatiles (H2O, F, Cl, and S) in lunar volcanic glass spheres (Saal et al., 2008) has led to a re-evaluation of the giant impact hypothesis. A new generation of measurements and experiments is increasing our understanding of the quantity and distribution of volatiles in the interior of the Moon. Our contribution to this effort has been to measure the solubility and diffusivity of water in lunar basalt under conditions similar to those thought to exist on the Moon. Knowledge of these parameters will help us to understand how volcanic fire-fountain eruptions are driven. They will also help us to better constrain the amount of water dissolved in the mantle sources of the lunar volcanic glasses, which will in turn provide an important constraint for lunar formation models.

Image: Apollo 15, NASA