Siobhan Kingham

Project Title: The Role of Water in the Moon’s Unique Chlorine Isotopic Signature

Without water, life could not exist on Earth. The presence of water also impacts the properties and behaviour of rock in the interior of Earth, and affects processes such as volcanism. As such, understanding the origin and early history of water in the inner Solar System is a key research area in earth and planetary science.

When a rock is formed, it can incorporate and preserve geochemical “signatures” from its environment, which act as tell-tale records of chemical reactions. Water was thought to be first supplied to the inner Solar System soon after the planets were formed, 4.4 billion years ago. Due to constant geological activity (i.e. plate tectonics), the geochemical evidence in Earth’s rocks formed during this time period has since been highly altered or destroyed. However, lunar rocks may be able to be utilised. The Moon was formed by a massive collision of a Mars-sized planet with the newly-formed Earth and contains a very small amount of water. Unlike Earth, the Moon has not been substantially reworked by geological processes for more than 3 billion years, and so may provide a window into conditions in the young Solar System.

A lunar geochemical signature of particular interest is that of the element chlorine. Chlorine is especially useful for tracking processes involving water, as it is both attracted to water and has a similar ‘volatility’ (the ease at which it can evaporate). Lunar rocks exhibit a unique chlorine geochemical signature which suggests that a large proportion of the original amount of lunar chlorine may have been lost from the Moon, which might mean that a significant amount of lunar water also escaped during this event. However, there is a great deal of uncertainty around what the lunar chlorine geochemical signature represents (i.e. what the event was which formed the signature) and how water was also affected.

I will therefore be conducting a series of experiments under recreated past lunar conditions, to test how water and chlorine may have escaped from the Moon, to see how the geochemical signature of chlorine might be altered during these events, and to therefore show how the lunar water content and observed chlorine signature are linked. Understanding this will shed light on processes which redistributed water soon after it first appeared in the Solar System.