In the detective business, the standard advice is: “Follow the money.” In human space exploration, perhaps somewhat similar advice applies: “Follow the water.” This needs debate, however there are some potent arguments in favor of the notion that human (as differentiated from robotic or probe) exploration of space should go where sources of water are available.

For one thing, people require water. After all, we humans are about 60% water by weight. (Crystalline life forms in a Star Trek Next Generation episode referred to humans as “Ugly bags of mostly water.”) Whenever humans venture into space, large quantities of water for a variety of uses must also travel along. Unfortunately, water is relatively heavy, and lifting it out of a gravity well – especially Earth’s – requires a lot of fuel. It’s also somewhat troublesome to store and maintain. Therefore water aboard spacecraft is very expensive.

For another thing, water, when split into two parts hydrogen and one part oxygen, can be used for (at least) two extremely valuable quantities: Oxygen, which can be used to make the air we breathe, and rocket fuel.

There are other more miscellaneous uses for water: Solvent, coolant, lubricant, hydrant (as in hydration of food).

For human space travel water is a necessity. It’s obvious that if water can be obtained other than from Earth (and its gravity well), there are big cost advantages.

New Sources of Water on the Moon

That’s why finding water on the Moon is such a big deal. Until recently it was assumed that the Moon was a very, very dry place. Drier by far than any desert on Earth. Now we believe there is water in minute quantities in the surface regolith most places on the Moon, and more importantly that there are ‘significant’ quantities of water in shadowed craters at the Moon’s poles. The bottoms of these craters have not seen the light of the sun in billions of years. They are ‘cold-traps’ with temperatures in the range of -220 degrees Centigrade (-370 degrees Fahrenheit). The water-ice in these craters is too cold to evaporate, and has been collecting there for a long time.

They key word is ‘significant.’ While some water molecules are found on the surface of the Moon, extracting it from many tons of material (mostly very powdery and machine unfriendly dust) is probably an engineering nightmare, if not a fantasy. In contrast, the water in the polar craters may actually be in the form of ice, which requires little more than melting and cleaning. The interesting question, which should be answered by further research and probably additional Moon probes is: How much water? Water for human consumption doesn’t require vast quantities, but the supply has to be readily available. Water for rocket fuel is another matter. Even small rocketry would require many tens of thousands of liters.

The Moon has Competition

The Moon is not the only place in the solar system with water (ice). We know that Mars has water, a lot of it, possibly oceans of it. Europa, one of Jupiter’s large moons, quite possibly has a liquid water ocean underneath the surface ice. Enceladus in the Saturn system of moons is composed mostly of ice and some water. These and several other moons with water are potential destinations for human space travel, although they are very distant. The nearest, Mars, would require about six months (give or take) each way.

Another potential source of water are the asteroids, both those that are found in the Asteroid Belt (between Mars and Jupiter), and more practically in those that orbit into the inner solar system. Among these are the so-called Near Earth Objects (NEOs) that periodically pass through ‘the neighborhood’ of the Earth. Some of these objects are asteroids or comets known to have high water-ice content. Because they are small (no significant gravity well) and pass relatively near Earth, some NEOs would actually require less energy to visit than the Moon.

Water Beckons

While the presence of usable quantities of water is not the be-all-end-all of human space exploration (and has no direct relevance for non-human space exploration), it’s obviously convenient. The economics of using water for fuel are particularly attractive. As we’re coming to realize, all other motivations aside, it’s money that makes space exploration possible. So perhaps following the water is following the money.