The Moon is a fascinating place; there is no two ways about it. Like many bodies within the solar system, it is proving to be a lot more surprising than we’d previously thought. Up until 2009, for example, it was accepted that the Moon was a dry, arid place with little or no subsurface bodies of water ice. This idea was turned on its head in 2009 after India’s first lunar mission, Chandrayaan I, and NASA’sLunar Reconnaissance Orbiter (LRO) confirmed the presence of water ice within the so-called permanently shadowed regions (PSRs) – deep craters around the lunar poles which never see direct sunlight in their basins.
However, one of the questions surrounding these discoveries is just how much water might actually exist as ice within these shadowed craters? A new study, published in August 2018, has sought to address this question; it is the work of Shuai Li – a post-doctoral researcher at the University of Hawaii, and produced with the assistance of researchers from Brown University, the University of Colorado Boulder, the University of California Los Angeles, John Hopkins University, and NASA’s Ames Research Centre.
Li’s study focuses on data returned by NASA’s Moon Minerology Mapper (M³), flown aboard the Chandrayaan I mission. M³ was designed to measure light being reflected from the illuminated regions on the Moon, making its use over the PSRs had been considered of minimal value. Nevertheless, Li believed that what data M³ had gathered on the south polar craters might hep in determining the potential volume of water ice within those craters, as indicated by the Lunar Orbiter Laser Altimeter (LOLA), Lyman-Alpha Mapping Project and Diviner Lunar Radiometer Experiment on the LRO mission. However, what he found came as a complete surprise.
While I was interested to see what I could find in the M3 data from PSRs, I did not have any hope to see ice features when I started this project. I was astounded when I looked closer and found such meaningful spectral features in the measurements … We found that the distribution of ice on the lunar surface is very patchy, which is very different from other planetary bodies such as Mercury and Ceres where the ice is relatively pure and abundant. The spectral features of our detected ice suggest that they were formed by slow condensation from a vapour phase either due to impact or water migration from space.
– Shuai Li, leader of the study team
While likely the results of vapour capture following asteroid impacts, Li’s study again opens the door as to how much sub-surface water ice might also exist deeper within the polar regions of the Moon. As I recently noted, a separate study, evidence has been put forward for periods in the Moon’s early history when liquid water existed on the lunar surface at a time when the Moon had a volcanically-induced atmosphere. Much of this water was likely lost to space as that atmosphere dissipated at the end of the Moon’s active volcanic period; however, some of it may have gone underground again, notably in these polar regions.
Either way, the existence of water ice deposits strengthen the case for a return to the Moon and – as NASA Administrator Jim Bridenstine recently indicated – see the establishment of a permanent human presence on the Moon. An available and plentiful supply of water would go a long way to easing many of the logistical requirements for such a human presence. Once melted, a local supply of water can be filtered and purified to provide drinking water; it can also be used in construction work and as “grey” water for use in growing local foodstuffs through hydroponic or other means; it can be electrolysed to produce oxygen in support of the atmosphere within a base and hydrogen than could be used to power fuel cells, and so on.
The European Space Agency (ESA) in particular is researching ways and means to build a lunar settlement using what is called “in-situ resource utilisation” (ISRU), or the use of locally available materials. In particular ESA has been using locally available “lunar simulants” available here on Earth – notably certain types of volcanic dusts that have been shown to have very similar properties to the dry dust of the surface-covering lunar regolith on the Moon – to test potential options for base construction.
One of these I’ve again previously written about, is the idea of using regolith to effectively “3D print” a protective “shield” of regolith over the facilities of a lunar base to protect it against solar radiation. Referred to as “additive manufacture”, such a technique might be aided with a readily available source of water which can help mix the regolith into a cement-like form that can be “printed” over the structure of a base in layers. In addition, ESA is using a regolith simulant to make “bricks” which can be used to physically construct the walls, floors and ceilings of a base – a process that might again be easier with a supply of water for use in the process.
But it is in production of oxygen and hydrogen, as well as offering a source for liquid water, that the ice deposits offer the greatest potential benefit. Up until now, ideas for oxygen production on the Moon have focused on “cracking” the regolith to release the oxygen within it (thought to be around 40% by volume). This requires a lot of energy to achieve – more than is needed to melt and electrolyse ice to produce both oxygen and hydrogen.
However, it’s not all plain sailing for humans on the Moon. The dust comprising lunar regolith is extremely electro-statically charged, making it stick to just about anything – so keeping it out of a lunar habitat could prove difficult. Worse, it also presents a range of potential health hazards – up to and including major respiratory problems such as lung cancer. These risks have yet to be fully assessed, and countering them as far as possible must be a priority before there can be real talk of a long-term human presence on the Moon.
But in the meantime, Li’s study potentially adds important food for thought for those thinking about establishing research facilities on the Moon.