Water on the Moon - We are the Aliens
Over the past week NASA teased us this big press release - and today they announced that astronomers had found water on the Moon. But if you've been paying attention to science news for a few years you'll know that the presence of water ice on our satellite is not a new discovery [1].
So what is the big deal?
In my opinion, the answer lies less with science than it does with marketing and business, but before I share my (potentially controversial) two-cent, here is what you need to know about the discoveries.
Disclaimer: I do not speak for NASA or my institute. I am just an opinionated astronomer.
The Science
The press release actually concerned two Nature Astronomy publications: The first by Honnibal et al. presented smoking-gun evidence of water in the exosphere (a.k.a very thin atmosphere) of the Moon based on observation taken with the SOFIA telescope. In case you’re not aware, the coolest things about this telescope is that it is literally on a plane. Anyways, using the data they obtained, the authors estimated the abundances of molecular water to be between 100 and 400 part per million. In the publication a few potential traps for Moon water are mentioned:
Impact glasses: rocks that are formed following an asteroid impact as the molten lunar surface cools rapidly.
Shielded locations (from the Sun’s harsh radiation) between lunar grains
Overall they suggest that the most likely reservoir is the impact glasses. Yup, turns out water can be trapped in rocks - if I'm honest I was as surprised as you are. All in all, this could be a great opportunity for water mines.
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The Hayne et al paper is a little different - it focuses on identifying Micro-cold traps: that is, areas of the Moon that are permanently shielded from solar radiation and whose temperature doesn't exceed 110 K (roughly - 160 C). Now, it's important to note that they are not claiming there is water ice in all of those traps. These are just opportune locations for ice to settle. The main finding in this study is that small traps ~1m to 1cm in size are the most numerous. Although this is cool, because volume goes with distance cubed, even if most of your cold traps are small, the volume of water ice will be dominated by the large ones - here is a concrete example:
A 1cm x 1cm x 1cm ice cube contains 1 gram. In contrast, an ice cube of dimensions 1m x 1m x 1m will weigh one MILLION grams .
Increasing the sides by a factor of 100 increases the volume by a factor of 1 million.
Nevertheless, these micro-cold traps add another 10-20% to the total area of cold traps on the Moon according to their study. Another interesting point they highlight is a disparity between the Northern and the Southern hemisphere: the later has more cold traps larger than 10 km. If they’re filled with water ice, those could also be a great source for water mines.
By now you might be asking yourself why in hell I keep talking about water mines. We’re getting there, I promise.
The Implications
When we hear about astronomers finding water somewhere in our Solar System we often associate it with the possibility of extra-terrestrial life, because in our experience water is one of the key ingredients to all living things on Earth.
In the case of the Moon however we're not even remotely considering the possibility of Life. The Moon is not Mars - a whole planet with a history of plate tectonics [2] and even liquid water [3] [4]. The Moon is not Europa, a large satellite with a large ocean underneath its ice crust [5] which could potentially harbour niches similar to those where life began on Earth (hydrothermal vents [6]).
The Moon, in essence, is a big rock.
So why do we care about finding water on the Moon? So it's a wet rock now, what's the big deal? Well, you see, water is precious - in space even more so than on Earth. And water is very useful. Obviously it's a part of an astronaut's balanced diet and could be a handy resource if, say, we were to create some sort of outpost on the Moon. But we're actually pretty good at recycling water - the International Space Station is pretty much a closed system. Any water that you sweat, cry or piss out will be cleaned and made drinkable again. Still, extra water is nothing to spit on, and could even be used to grow plants and food.
But truly the most interesting thing you can make with that water is not food; it’s another kind of fuel:
Rocket Fuel
Yes, rocket fuel. You need but two ingredients: liquid hydrogen and liquid oxygen. H2O very conveniently provides both components. Now you might be wondering - why don't we just make that fuel on Earth rather than go mining the freaking Moon. Indeed a valid concern.
See, the Earth has a tremendous disadvantage over the Moon - its gravity (it's about 6 times greater). As it turns out, the most expensive (energy-wise) step of space travel is escaping the gravitational pull of our planet - so even if we can make a lot of fuel on Earth we also have to use a lot of it to get it off. For advanced space travel (e.g. going to Mars on the regular, or mining asteroids) it would be awfully convenient if we could make fuel off the planet, in a nearby outpost that is relatively easy to get to, maybe a satellite of some sort that also contains water reservoirs... *wink wink*
This probably sounds like science fiction…
But what if I told you that in May 2020 the US and 7 other countries signed the Artemis Accords [7] which, amongst other things, start outlining regulations on the mining of the Moon and asteroids - see Section 10.2. In essence it states that extracting resources is not a breach of the Outer Space Treaty [8]. And if you’re still not convinced, guess why, JPL has a bloody infographic to tell us exactly how that sort of back breaking work could be carried out [9]. Long story short, when you hear people getting excited about water on the Moon, don't think "Aliens", think "rocket fuel".
I guess in this case, we are the aliens. Let's just hope that we can share outer space better than we can share the World.
My opinion and worries
The next few decades are going to be interesting to say the least. Billionaires are already making space their playground and monetising the night sky. If you think Elon Musk made StarLink out of the kindness of his heart and not for profit, get off my website. Mining asteroids, a Moon base, all this may sound crazy today but if there is money to be made it could be the next target of the ultra-rich, pretend-Tony-Starks, of the world.
I wish that space travel was driven by curiosity and the pure love of science, but at the end of the day the great accomplishments of the space race in the 60s were driven by a pissing contest between two super-powers, so I wouldn't be surprised if the next leaps in humankind's space adventures were driven by greed and ego. My only hope is that the scientists will manage to gather data along the way and that whatever riches we find off-world will not work to exacerbate inequalities on our blue planet. And if we end up turning the Moon into a petrol station, please let us do it responsibly and not deplete non-renewable resources on other worlds the way we did to our own.
I’m going to be honest… I’m not very optimistic, but it might just be the 2020 talking.