Oct 27 2020

Water on the Moon

Published by under Astronomy
Comments: 0

A new paper published in Nature Astronomy presents further evidence for significant water near the surface of the Moon. This is exciting news for the prospects of a lunar base, especially since NASA is planning on returning permanently to the Moon by 20204.

The Artemis program (Artemis is the twin sister of Apollo) plans to put the first woman and the next man on the lunar surface by 2024. Even if they don’t meet this ambitious timeframe, they will likely succeed sometime this decade. Unlike the “flags and footprint” mission design of Apollo, Artemis is designed for sustained exploration of the Moon. Artemis will use the space launch system, which will be the most powerful rocket in the world. In fact, the most powerful configuration of the SLS will be more powerful than the Saturn V rocket. This is because the SLS was designed no only to return to the Moon, but to be powerful enough to get to Mars, which is the ultimate goal.

On top of the SLS will be the Orion capsule, NASA’s deep space capsule. Orion can accommodate up to four astronauts, and is designed for multi-week missions. It will have exercise equipment, radiation shielding, and on board waste disposal. When they get to the Moon they will have a new lunar lander, currently in development. But unlike Apollo, NASA also plans on building the Gateway – a lunar orbiting platform for long term occupation and exploration of the Moon.

After the initial Artemis missions, NASA plans to create a basecamp near the south-pole of the Moon for long term occupation and exploration of the Moon. Why the south pole? In NASA-speak the poles, “may contain mission-enhancing volatiles.”  In addition “These sites may also offer long-duration access to sunlight, direct-to-Earth communication, surface slope and roughness that will be less challenging for landers and astronauts.”

By “mission-enhancing volatiles” they mostly mean water. It is expensive and difficult to bring stuff to the Moon, and so the more local resources we can use the better. This is where this latest study comes in. Prior research has detected signals of possible water near the lunar poles. As the authors report:

Widespread hydration was detected on the lunar surface through observations of a characteristic absorption feature at 3 µm by three independent spacecraft. Whether the hydration is molecular water (H2O) or other hydroxyl (OH) compounds is unknown and there are no established methods to distinguish the two using the 3 µm band.

So they detected what might be water but also might be other chemicals containing OH. This could still be useful to have, but water would be better. The new study examined the lunar surface in the 6 µm band, which is capable if distinguishing molecular water from related OH compounds, and they found – lots of water, but only in the high latitudes (i.e. near the poles). How much water?

Speaking during a virtual teleconference, co-author Casey Honniball, postdoctoral fellow at Nasa’s Goddard Space Flight Center in Maryland, said: “The amount of water is roughly equivalent to a 12-ounce bottle of water in a cubic metre of lunar soil.”

The first few centimeters of lunar regolith is “desiccated” according to the study, but underneath there is lots of water. This water is trapped inside impact glass – glass formed when meteorites strike the lunar surface.  So it would have to be extracted, but that should not be difficult.

All this makes the poles really attractive as a sight of a long-term base on the Moon. The regolith might also be usable as a form of building material, so we can build structures and extract water as we go. Of course, while this is a significant amount of water it is not very much compared to what people need to live, especially if they are also growing plants for food. They would need to fairly efficiently recycle the water, which again should not be difficult in the closed environment of a lunar base.

It appears that the lunar poles, therefore, have everything for an optimal location for a permanent base on the Moon. However, there is one other feature that might be ideal for a permanent base – lava tubes. A lava tube is basically a cave under the lunar surface formed by ancient flows of lava up from the depth of the Moon to the surface. The heat melted the rock into a solid wall, and there may be sections which remain intact and secure. We can sometimes see on the surface of the Moon places where the roof of a lava tube collapsed near the surface, potentially providing access to the tube.

One possible lava tube was found near the North pole of the Moon, but I have not seen any reports of such tubes near the South pole. A polar lava tube could be the ideal location for a Moon base. The reason a lava tube would be useful is because the Moon has no significant magnetic field or atmosphere to protect the surface from radiation or micro-meteors. Any base would have to be shielded to protect the astronauts within. A lava tube is deep underground, providing natural shielding. Because of the Moon’s low gravity they are also huge. Some estimates are that lunar lava tubes could be kilometers across, big enough to hold entire cities.

It seems pretty clear that “volatiles” are going to be critical to the long term survivability of any lunar residence, whether a research base or ultimately lunar settlements. Water and oxygen will be critical. At first these will have to be brought to the Moon from Earth, but that is a long and expensive supply chain. If there is significant water on the surface of the Moon, even if only at the poles, that could make the viability of such a base much higher. But I wonder how practical this will be, and if it will provide enough water for a large presence. We will likely still need to transport lots of water to the Moon. We may also ultimately mine asteroids for volatiles and bring them to the Moon from there. That may ultimately be cheaper, as you won’t have to lift them out of the gravity well of the Earth (which is what uses most of the energy).

Either way, the presence of significant amounts of water near the surface of the lunar poles is an exciting discovery, and does bode well for the prospects of a lunar base.

No responses yet