Moon Water - Our Ticket to the Solar System!

Dr Jamie Love 12 March 1998 ©

I was a teenager during the Apollo years and I watched with excitement as the astronauts bounce around our first "alien world". The Apollo program ended prematurely nearly three decades ago and analysis of the rocks returned showed that the Moon was rich in minerals and metals, but it had no water. Although this was a disappointment it came as no surprise. Scientists had long speculated that the Moon would be dry.
This was based upon our understanding of how water should behave on the surface of the Moon.

Sunlight falling on molecules of water will heat them, causing them to wiggle violently and move rapidly. This is caused by the transfer of energy (sunlight) to the water molecules. It happens on Earth too, but on the Moon it happens to a much greater degree for three reasons.

First, there is no atmosphere on the Moon, so there is nothing to shield the water from the sun's powerful rays. Second, the lack of an atmosphere on the Moon means that water molecules will not be slowed down by bumping into other molecules so they are able to maintain their speed. Third, the Moon takes four weeks to rotate around its axis so its "daytime" lasts 14 (Earth) days, so there's plenty of time for the water on the Moon to be heated by the sun.

These three factors mean the sunlight will cause any water molecules on the Moon to move VERY rapidly.

Water molecules on the Moons' surface exposed to the rays of the sun for days on end will pick up so much energy and move so quickly that they will reach "escape velocity". Escape velocity is the velocity (speed) needed to escape the gravitational pull of a planet or moon.

No, that's not completely true. You never truly "escape" a planet's gravitational pull. Gravity extends throughout the universe, but its force drops quickly with distance so it's easy to think that after a certain distance you have "escaped" from it. When something reaches and maintains escape velocity the gravity from the planet (or moon) can no longer pull it back; although it is still pulling, at least a little. Because of this little bit of constant pulling, some physicists might argue that there is no such thing as "escape velocity", because you never completely escape the gravity of a planet. However, engineers who work with more practical definitions, explain that this little bit of tugging can be ignored, in most cases, so escape velocity is a real and useful value. If a molecule of water, or a rocketship, can achieve escape velocity and maintain it for long enough, it will "escape" from the planet or moon. Escape velocity is important to astronomers seeking molecules on other worlds and it's important to engineers designing rockets to get there! The Moon has much less gravity than the Earth, about 1/6th, because it is much smaller than Earth, so the Moon's escape velocity is much lower than the Earth's escape velocity. That means it takes less energy to launch water molecules or rockets from the Moon than from the Earth.

Another important difference between launches from the Earth or the Moon is that the Earth's atmosphere gets in the way. Atmosphere causes drag and drag slows things down. The drag caused by the Earth's atmosphere works against a rocket or a water molecule. That means it's harder to MAINTAIN escape velocity through the Earth's atmosphere. Atmospheric drag is a big problem for rocket engineers.

Rockets launched from the Earth are designed with smooth, streamline shapes in order to help push the atmosphere aside and let the rocket get through with as little drag as possible. Rockets launched from the Moon do not have to fight through an atmosphere. They experience no drag, so they can be any shape. The rocket that launched men from the Earth to the Moon (a Saturn V like the one on the left) was streamline. The rocket that launched men from the Moon to the Earth (the Lunar Excursion Module, or LEM, on the right) looked like it was built to stand still!

We will come back to this important difference between the Earth's and the Moon's launch requirements near the end of this article when I will tell you how the Moon will be used to launch Man's first serious space colonization efforts.

What about the water? It sounds like all water on the Moon should have reached escape velocity.

Yes, that's what you might expect. However, some space scientists (Watson, Murry and Brown way back in 1961) wondered if there might be water frozen in the permanent shadows on the Moon. To understand these permanent shadows requires some explanation and that starts with an understanding about the tilt of the Moon.

The Moon's axis is titled only 1.6^o from its orbital plane. By contrast, the Earth's axis is tilted 23.5^o from its orbital plane and that tilt is responsible for the Earth's seasons. Here on the Earth the length of each day's "daytime" (or "daylight" if you prefer) varies considerably from place to place and from one time of year to another. That's because of the Earth's excessive tilt. The tilt of a planet also affects the height the Sun can reach above the horizon. At the Earth's poles the Sun NEVER rises more than 23.5^o above the horizon because that is the angle of tilt of the Earth from its orbital plane. To create a place of permanent shadow at the Earth's poles you would need a deep, narrow crater (shaped like a well).

On the other hand, at the Moon's poles the Sun rises no more than 1.6^o above the horizon because that is the angle of tilt of the Moon from its orbital plane. You don't need a particularly deep or narrow hole to make a permanent shadow at the lunar poles.

Most craters near the Moon's poles have areas of permanent shadow. The crater's rim shields the bottom from the rays of the sun.

The poles of any world experience extremes of "daylight" because sunlight can barely reach them. Indeed, the surface temperature in the Moon's permanent shadows doesn't rise above -170^oC (or -280^oF if you use ancient temperature readings)! Here on Earth such extreme cold is never reached, even in the shadows at the poles, because the Earth's atmosphere circulates around moving heat into the shadows. The Moon has no atmosphere so it has extremes of temperature. Sunlight heats the Moon's sunlit surface to above the boiling point of water but, only a meter away in a shadow, the temperature is so low that water freezes into ice!

Much of the Earth's water has probably come from comets. Our solar system is full of comets and comets are full of water (ice). Comets have been smashing into the Moon and Earth for billions of years.

On the Earth the evidence of comet impact, the craters, is eventually destroyed by the weather but the watery contents of the comets remain. Luckily for us the Earth's higher gravity and atmosphere make it difficult for water molecules delivered by comets to reach the high escape velocity needed to escape from the Earth. Unluckily for the Moon, its lower gravity and lack of atmosphere make it easy for water molecules to be heated to lunar escape velocity by the sunlight.

The water at the bottom of a polar crater, hidden in its permanent shadow, stays put. As a matter of fact, these polar craters may actually capture water molecules as they pass by.

Imagine a comet hits the Moon - anywhere on the Moon. It explodes. Its water molecules get heated by the sun and they start to move around. Most of these molecules reach escape velocity and are lost from the Moon, but some slower moving water molecules wander over the Moon's surface, turning to ice when they fall into a temporary shadow and then back into steam when the shadow has moved on. These water molecules keep changing back and forth from ice to steam, ducking in and out of moving shadows, as they wander randomly over the surface of the Moon. Some of these migrating water molecules may eventually wander to a pole and become trapped in the permanent shadow of a polar crater! Then their migration stops. They are trapped in the bottom of the lunar crater "forever".

So, why didn't the Apollo astronauts find any water?

Because they never went to the poles. Instead, they explored the equatorial regions of the Moon because it was easier to get there, land there and go about their work with the Sun high overhead.

We might still be ignorant about the Moon's water if not for a satellite called Clementine.

Throughout the late 1980s the United States Department of Defense (DOD) was working on a variety of high-tech space projects which most people know by the nickname "Star Wars". Among the various plans was one to use remote-controlled satellites to track, and eventually collide with, targets in space. The military wanted to test their instruments and ideas but they were prevented by certain regulations regarding weapons in space. So they teamed up with NASA to find some common objectives that would have a more "civil" purpose. Space scientists were keen to get a vehicle close to some asteroids in order to collect data that might one day be used to mine them. NASA was happy to help the DOD spend some money on the joint project that was named Clementine (after an old American mining song) to emphasise the potential mining aspect of the project.

On the 24th of January 1994 Clementine was launched from Vandenburg Airforce Base (California, USA). The 140 kilogram satellite carried an array of instruments including a very good radar system. After a few weeks in Earth orbit Clementine was sent to the Moon. For two and half months Clementine circled the Moon in a highly inclined orbit, mapping the polar regions in very good detail. That had not been done before by any other satellite and it's impossible to do from Earth. During one particular orbit over the South Pole, Clementine used its radar to measure the reflectance of polarized radio waves. (It's a pretty complicated way to estimate the "texture" of a distant surface.) Data from that single orbit proved to be very interesting!

On the 3rd of May 1994 Clementine was ordered out of lunar orbit on its mission to rendezvous with an asteroid called Geographos. A computer software bug caused the satellite to lose control and it never achieved its mission object. Clementine never made it to Geographos but the data it collected from the Moon's poles was available for NASA scientists to study.

Some of the scientists interpreted Clementine's radar data as consistent with the possibility of water ice being in the permanently shadowed craters near the Moon's south pole in a place called the Aitken Basin. The Aitken Basin is a giant impact crater and it's the largest and deepest known crater in the Solar System! Calculations suggested that the total ice coverage was over 30 square miles, although it was scattered all around the basin. Other scientists pointed out that the radar data might be interpreted another way that meant there was no ice there at all. Clementine had not been designed to look for water on asteroids or the Moon so Clementine's data was open to different interpretations and arguments. The only thing that would settle the argument would be a special mission to observe the lunar poles with equipment specially designed to look for water.
That's what Lunar Prospector is all about.

Lunar Prospector is a 295 kilogram, graphite-epoxy, drum-shaped craft only 1.4 meters in diameter and 1.3 meters high. It has three masts sticking out of it, each 2.4 meters long, to which the sensory instruments are attached. The instruments were placed on the masts to avoid interference caused by signals from the body of the craft. The spacecraft is solar-powered and uses rechargeable nickel-hydrogen batteries when it isn't in the sunlight. Lunar Prospector, or simply "Prospector", is part of NASA's Discovery program to develop missions that are "faster, better, and cheaper". Prospector was created in just 22 months, so it certainly was "fast". Some of NASA's missions have had trouble because they used specially designed and manufactured equipment for each spacecraft. Prospector uses "off-the-shelf", flight-proven equipment, and it's designed to get the job done without getting fancy. That makes it "better". Prospector cost a "cheap" $63 million, a small price for almost any spacecraft and a real bargain for starting us on the road to colonizing space!

On January 11th Lunar Prospector went into a polar orbit 100 kilometers above the Moon. Next year it will be ordered into an orbit as low at 10 kilometers to give us even better information! The spacecraft carries five different scientific instruments designed to sense chemical and physical properties of the Moon.

The Magnometer measures both the strength and direction of the magnetic fields around the Moon. These magnetic fields are produced mostly from the Earth and Sun, but when they are subtracted from the data you are left with the magnetic field produced by the Moon. This information will help NASA geologists to map the location of magnetic deposits like iron.

The Electron Reflectometer measures electrons reflected (bounced) from the surface of the Moon. These electrons are reflected off of magnetic materials in a very specific way. (It has to do with some complex geometry.) This instrument will complement the Magnometer as NASA produces its "magnetic map" of the Moon.

The Gamma Ray Spectrometer measures gamma rays (obviously). Gamma rays are produced when certain radioactive materials undergo their natural decay, so this instrument will be able to map the locations and concentrations of radioactive materials on the Moon's surface like uranium and thorium. Perhaps one day these will be mined to provide nuclear power for missions into deep space where the use of solar energy would be impractical.
Gamma rays are also produced by nonradioactive elements when they are struck by powerful cosmic rays so, Prospector's Gamma Ray Spectrometer can be used to sense nonradioactive elements too. Cosmic rays are not rays at all (!), they are extremely high-speed, subatomic particles. Cosmic "rays" are common in space, falling onto the Moon (and Earth and everything else) from all directions, so they are constantly striking materials on the Moon's surface and producing gamma rays that Prospector can detect.
The interesting thing about a gamma ray, regardless of how it is produced, is that the energy of the gamma ray tells you what element emitted it. So this device will allow NASA scientists to map the location of uranium and thorium (directly by the gamma rays they emit as they decay) and iron, oxygen, silicon, aluminum, calcium, magnesium, and titanium (indirectly by the gamma rays they produce when hit by cosmic rays).

The Alpha Particle Spectrometer measures another product of radioactive decay. Alpha particles are the nuclei of a helium atom (two protons and two neutrons). Although not as versatile as the Gamma Ray Spectrometer, this instrument works in a similar way and will give us information about the small amounts of radioactive gases released from the Moon. Gases released from a planet are an important geological phenomenon, called outgassing. The Alpha Particle Spectrometer will provide more clues about the Moon's composition and evolution.

The Neutron Spectrometer measures neutrons and it is the most important instrument on Lunar Prospector because it's the gizmo that proves there is water on the Moon!

How? Neutrons are just neutral atomic particles. How can you sense neutrons?

Good question. You do it indirectly. Let me tell you how Prospector's Neutron Spectrometers detects neutrons.

First you should know that it isn't really one instrument but two almost identical instruments. They are both tiny canisters containing a special gas called helium-3 (or ³He to use the proper symbols). ³He is made of two protons and one neutron. The two protons give the atom its "elemental characteristics". That is, these atoms are helium atoms because they contain two protons in their nucleus. The neutron doesn't really influence any chemical properties so it's easy to think of it as just extra mass. (Which it is!) However, it gives ³He special nuclear properties.

When the 3He is hit by a neutron it exchanges one of its protons for the neutron. The result of this nuclear reaction is that the 3He is transformed into a new element (hydrogen-3 or 3H, an isotope of hydrogen called "tritium"). In the process a proton and lots of energy is released. The burst of energy is detected and counted.

OK, that's how Prospector detects neutrons, but what's the point of two different containers?

One container is coated with tin that allows all neutrons, even very slow moving ones, to enter. The other container is coated in cadmium, a metal that screens out the slow moving neutrons, so only fast (high energy) neutrons can get through. This means you can use the two containers, side by side, not only to detect a group of incoming neutrons, but also to tell if those neutrons are moving fast or slow. Together the two containers allow you to divide the population of neutrons into high energy and low energy. That's what a "spectrophotometer" is all about!

Separately you have two neutron detectors, one more sensitive than the other, but both are merely detectors because all they do is detect and count neutrons. Together you have a spectrophotometer because by using the two together you can determine the amount of both levels of energy in a shower of neutrons.

Imagine a group of neutrons hits Prospector's Neutron Spectrophotometer (both detectors). Suppose the tin detector, the more sensitive detector, counts 10 neutrons. (Actually the detector counts the burst of energy produced by the nuclear reaction described above, but you know what I mean.) Also, suppose the cadmium container counts only 8 neutrons. That means the 2 "missing" neutrons were too weak, too low in energy, to pass though the cadmium walls. By using the data from both containers you can say that the population of neutrons that hit Prospector's Neutron Spectrophotometer is composed of 80% high-energy and 20% low-energy neutrons. That's useful data!

So, what does this have to do with water?

Everything.

To put it all together you need to learn where the neutrons come from and how they behave when they hit something.

You'll recall that cosmic rays are all over the place and they constantly bombard the surface of the Moon producing gamma rays which Prospector's Gamma Ray Detector can use to map the location and concentration of elements that don't normally produce gamma rays (like iron, silicon, etc.). Well, that was only part of the story. When cosmic rays strike an atom they not only release gamma rays but also dislodge neutrons that go flying out of the atom at a very fast speed. We call these very fast neutrons "hot" neutrons. Most of them fly off into space but some of them will collide with materials in the Moon's surface and are slowed by the collisions. Because the collisions slow them down we say the neutrons have "cooled", or their speed has been "moderated". How much they are moderated (cooled) depends upon what they hit. This has to do with momentum and is best illustrated with marbles!

Think about how you play a game of marbles. Recall how a marble behaves when it hits a stationary marble. Both, being similar in mass, will fly off in opposite directions. The stationary marble will move away at half the speed of the striker, which moves away at half its original speed. On the other hand, if you rolled the marble against a bowling ball it would not budge, and the marble would fly off at pretty much the same speed it had to begin with. Imagine this "marble game" at the subatomic level with a neutron playing the part of the incoming marble. If a neutron hits an atom with a large nucleus the neutron will bounce off with only a slight loss in speed. Its speed will have been moderated only slightly. On the other hand, if the neutron hits a small nucleus it will be slowed down more because it will transfer more of its energy (momentum) to its target. When a neutron hits a nucleus with the same mass as that of the neutron the incoming neutron will bounce off at only half its incoming speed (just like when a marble hits another marble).

OK, last time! What does this have to do with water??!!!

Everything.

Water is made of one oxygen atom and two hydrogen atoms (H₂O). Hydrogen is the simplest atom in the universe because hydrogen is made of only a single proton. (OK, it can sometimes have a neutron or two but that's rare.) Protons and neutrons are identical in mass (almost). When a neutron hits a hydrogen nucleus (a proton) it bounces off at half its original speed. If it bounces off another hydrogen it loses half its speed again. The more hydrogen atoms in the neighborhood the more the neutron collides with them, and the slower or "cooler" it gets. Hydrogen in the water is a perfect neutron moderator!

Now is a good time to put all these thoughts together.

Neutrons bounced off any element other than hydrogen are moderated only slightly. Scientists call these medium energy neutrons "epithermal" neutrons and both detectors can sense them. Neutrons bounce off a hydrogen nucleus at half their original speed. The more water around them, the more the neutrons' speed is moderated. Scientists call these slow neutrons "thermal".

These slow, low energy, thermal neutrons cannot pass through the walls of the cadmium detector but they can make it though the walls of the tin detector.

When Prospector passes over a crater containing ice it will detect an increase in the number of thermal neutrons and a decrease in the number of epithermal neutrons, because the hydrogen in water causes the neutrons to become more moderated.
(Read that sentence again and make sure you understand it.)

Wait a minute. Water isn't the only thing that contains hydrogen.

That's right. Here on Earth we find hydrogen in lots of different things, especially living things, but hydrogen doesn't combine well with materials like rocks. On the surface of the Moon there is very little that hydrogen can bind to except oxygen. So water is the most likely source of the hydrogen signal.
Note: the "solar wind" can also "stick" hydrogen to the surface of the Moon by different means, but this hydrogen doesn't amount to much.

Prospector's Neutron Spectrometer is a very sensitive device and it's able to detect water hidden slightly below the surface (about half a meter down). That's because the cosmic rays that produce the neutrons can penetrate pretty deep and the neutrons they produce can bounce around a lot before making their way to the surface. NASA scientists estimate that Prospector's Neutron Spectrometer can sense a cup of water distributed in a cubic meter of lunar "soil".

The vertical axis is the number of medium energy (epithermal) neutrons detected. The horizontal axis shows the location (latitude) at which Prospector collected those neutrons. Notice that more epithermal neutrons were detected along the Moon's equator ("EQ" or Latitude 180) than at the North Pole (latitude 90 degrees) or South Pole (latitude 270 degrees). Recall that cosmic rays hit the Moon from all directions so neutrons must be produced at the same rate all over the Moon. Prospector's detector counted fewer medium energy neutrons at the poles because something there is slowing down the neutrons, moderating them. Water hydrogen is the most likely explanation for this moderation of neutrons.

Notice that there are dips at both poles. Clementine's data suggested that there was water only at the South Pole (Aitken Basin) but Prospector proves there is water at both poles. Also, notice that the dip in the number of neutrons is about the same in both poles (reaching a low of about 585 neutrons) but the dip is more pronounced at the North Pole than at the South Pole. NASA scientists estimate that there is about 50% more water at the North Pole than at the South Pole.

Note: NASA has been able to use Lunar Prospector's Gamma Ray Spectrometer to add to the epithermal neutron data because it has a "shield-detector" (which I won't go into) allowing it to detect epithermal neutrons. So Prospector has TWO ways to measure epithermal neutrons.

Another hidden feature in the data is that the amount of fast (hot) neutrons detected indicates the "mixing ratio" of the ice in the "soil". In other words, it lets you know if there are solid chunks or tiny crystals of ice. Data from Prospector (not shown here) indicate that the water is in a very low mixing ratio, between 0.3% to 1.0%. That means most of the water is not chunks of ice but tiny crystals dispersed over a large area. To put it another way, the ice in the permanent shade is not ice puddles but a "permafrost"! That might make it more difficult to collect but at least we now know what to expect.

By carefully measuring the amount of "missing" epithermal neutrons, using much more data then shown in the above graph, NASA estimate the amount of water on the Moon at 10 to 300 million cubic meters (or 2.6 to 26 billion gallons, if you're old fashioned). Over the next few months NASA will collect more data and be able to give a more accurate estimate of the amount of water on the Moon. Next year, when Prospector is ordered into a lower orbit, NASA scientists will be able to make more detailed maps of the Moon's water resources and more accurately estimate the amounts. Prospector has certainly shown there's a lot of water on the Moon and over the next year the spacecraft will provide more useful data for our colonization of the Moon.

Why is all this so important?

We have known for decades that the Moon is rich in minerals but the apparent lack of water had been a disappointment. Water can be used to make oxygen for the colonists to breathe and rocket fuel to launch spacecraft to all parts of the solar system.

The first lunar colonists will be equipped with specially designed water-mining machines that will collect the wet, frozen lunar materials from areas of permanent shade and extract the water from it. The water will then undergo a simple electrochemical process called "electrolysis".

Electrolysis uses electricity to break up molecules. The electrolysis of water is a well-known process and it's easy to perform.

When an electric current is passed through water the molecules break into ions of oxygen (O=) and hydrogen (H+). The hydrogen cation (H+) migrates to the negative electrode (called the cathode) where there's an abundance of electrons produced by the electricity. At the cathode each hydrogen cation picks up an electron and shares it with another hydrogen cation which does the same. This creates a molecule of hydrogen gas (H2), held together by the sharing of two electrons. (That's called a covalent bond.) Oxygen anions (O=) migrate to the opposite electrode (called the anode) which has a positive charge because the electrical circuit has been set up to make that electrode deficient in electrons. At this electrode the oxygen anions give up their extra electrons and create molecules of oxygen gas (O2) held together by sharing the electrons they haven't given away.

On the Moon the electricity will be produced by huge solar arrays situated on top of towers. The geometry that causes the bottoms of lunar polar craters to have permanent shade also causes polar peaks to have permanent sunshine! If your solar array is situated more than 1.6^o above the horizon it will always have sunlight falling on it. The array will need to track the Sun as it circles around the polar horizon. The Moon has no wind and only 1/6 as much gravity so lunar solar arrays can be very big and pick up a lot of sunlight.

When you make hydrogen and oxygen gas from water you put energy into the reaction in the form of electricity. Electrolysis is a quiet, even peaceful, reaction. However, when oxygen (O₂) and hydrogen (H₂) recombine they release all that energy in a powerful explosion.

It makes great rocket fuel! Space vehicles will (carefully) fill their tanks with the oxygen and hydrogen gas produced by electrolysis of lunar water. They will then launch the spaceships from the Moon by mixing and igniting these two gases, producing water and a powerful thrust that will hurl them off the Moon and on their way to other parts of the solar system.

Why can't we do this on Earth?

We can and we do.

Electrolysis of water can be used to make plenty of hydrogen and oxygen. When hydrogen is burned by combining with the oxygen in air the energy released can be used to power engines, including cars. Water is the only waste product. It's an environmentally friendly way to make energy but it costs a lot to do the electrolysis. Electricity doesn't come free. Even solar powered electrolysis costs too much because the solar arrays that produce the electricity are costly. However, one day this may change.

On the Moon the economics are a bit different. There are no cloudy days on the Moon and no nights if you place the solar arrays more than 1.6^o above the polar horizon. More importantly, the oxygen and hydrogen gas produced on the Moon will be easily available to space travelers because the Moon is a MUCH better place to "fill up" a spaceship's fuel tanks. That's because of the Moon's better "launch requirements".

I promised at the beginning of this article that we would come back to "launch requirements". You will recall that the Earth is a lousy planet for launching space vehicles. The Earth's atmosphere causes much drag and complications like bad weather. The Earth's gravity is also an important factor. Space scientists like to say that the Earth is at the bottom of a "gravity well" of its own making. To launch a spaceship from the Earth the ship must climb out of Earth's gravity well using a great deal of energy and all that energy must be provided by the rocket's thrust. And it must fight the Earth's atmosphere as it goes through it.

The Moon, on the other hand, has a very shallow gravity well and no atmosphere so it's a lot easier to launch from the Moon than from the Earth.

People familiar with space travel like to use "delta-V" diagrams to illustrate how much speed, and therefore how much energy, is needed to get from place to place. The word "delta" is a Greek letter used to represent "change" and the "V" stands for "velocity". Here's a diagram showing some of the velocity changes need to get around. The length of each line represents the velocity change to move a spaceship from place to place. (It is NOT the distance to get there.)

The bigger the delta-V the more energy you need. You can use diagrams such as these to get an idea of the best ways to move around the Earth-Moon system. Note: these values don't take into account the drag caused by the Earth's atmosphere. You can see immediately that it is easier to leave the Moon than leave the Earth. The Moon's escape velocity is only 2.38 kilometers per second. To escape from the Earth requires a velocity almost five times as fast (11.2 kilometers per second). That's a lot of energy and we haven't even taken into account the drag. I've also drawn in the delta-Vs for some orbits. Let's take a closer look at them. First you will see that it takes 2.2 kilometers per second to reach lunar orbit from the surface of the Moon. Just a little more delta-V (0.18 km/s) and you could go from lunar orbit to complete lunar escape (2.38 km/s)! That means once you reach lunar orbit it's a simple matter to go to other parts of the solar system. Compare that with the delta-Vs from the surface of the Earth to a low Earth orbit. The Space Shuttle achieves these low Earth orbits and the Space Station will be parked in a low Earth orbit too. You could get a payload up to the Station in the Shuttle but it takes a delta-V of 8.6 kilometers per second. Once the payload is there it needs an additional 2.6 kilometers per second to escape completely from the Earth on an interplanetary mission. Clearly it takes less energy to launch an interplanetary expedition from the Moon than from the Earth. For a real surprise, let's look at the delta-Vs to get to a low Earth orbit. It takes 2.2 kilometers per second to achieve lunar orbit and another 4.1 kilometers to move on to the low Earth orbit. That's a total delta-V of 6.3 kilometers per second. (Just add them up.) Compare that to the delta-V to achieve the same orbit from the Earth's surface - 8.6 kilometers per second. That means it takes LESS energy to go from the surface of the Moon to the Station than to get there from the Earth!

Remember, the lower the delta-V the lower the energy needed. In the next century, people living in a low Earth orbit will probably drink water mined on the Moon because it is easier to transport Moon water than Earth water to an Earth orbiting space station! Indeed, most of the structure of a space station could be made on the Moon and then launched to a low Earth orbit.

It would make sense to use the Moon to supply all the fuel (produced by the electrolysis of lunar water) and perhaps even the "bulk" of an interplanetary ship itself. All you need from Earth would be the people and equipment. Eventually even they would be best when "made on the Moon"! Launching vehicles from the Moon does not harm any ecosystems, doesn't get delayed by the weather and, of course, you don't have to worry about drag.

Colonizing the Moon will launch our species on its greatest adventure. Once you climb out of the Earth's gravity well, there's not much of a reason to turn back!

Who owns the Moon's water?

In 1966 many of the United Nations, including the USA, signed the "Treaty on Outer Space". Basically it says that the resources in space do not belong to anyone because they belong to everyone. According to the treaty no country can own the Moon and therefore no country can own the water on it. This treaty, like many of the UN's international treaties, is really nothing more than a "gentlemen's agreement". It explains that the Moon can be used only for peaceful purposes. Like Antarctica, the Moon is meant to be nothing more than a research post. However, also like Antarctica, we may be compelled by economics to harvest the resources.
It would be awful if we are not "allowed" to utilise lunar resources to colonise space.

Indeed, as we approach the next millennium it makes sense that we evaluate our future and discuss our intentions about lunar colonization and development. If the 1966 Treaty and its negotiations are anything to go by, underdeveloped nations will argue that they have a right to as much of the lunar resources as the rich nations and will demand compensation or inclusion in any plans to mine it. If international "reality" is anything to go by, the Moon will be developed by the rich nations who will use it to move into space.

The 21st century will see mankind move to the Moon and further into the universe.

We will do this as a single worldwide initiative, a cohort of just the space-faring nations or maybe as a conglomerate of private industries.

Who knows?

What about building the lunar colony? Is this really "doable"?

Yes, it is "doable"!
For decades there have been plans on the drawing boards to build colonies on the Moon. These plans include details of how to mine the Moon for aluminum, iron and titanium as well as the manufacturing methods to make glass and steel. Apollo discovered plenty of minerals on the Moon, enough to build plenty of structures using solar (or nuclear) power to forge them.

Closed ecosystems have been developed, and continue to be developed, from which we can learn how to grow crops on the Moon and recycle the lunar colonies' atmosphere, water and other resources. Sadly, Apollo found very little nitrogen on the Moon so this element might have to be imported from Earth until a more convenient source can be found. On the other hand, maybe there's some frozen ammonia (NH₃) in the permanently shaded regions. Why not? Comets have ammonia as well as water and Prospector's sensors detect hydrogen. Hmm? I wonder how much of that hydrogen is frozen ammonia!

Certainly our first step will be to send a lander (probably a robot) to at least one pole in order to get more information and test some of our ideas about how to best mine the water. Such a lunar lander might even include a sample return. From the information a lander provides we will be able to make more detailed plans about how and where to set up a lunar colony.

The discovery of water on the Moon could be the most important discovery since Man learned to use the winds to sail his ocean ships. It could open up new worlds, new adventures and new possibilities. We have the technology and the know-how to make it work.

All we need is strong political willpower to move us into space. We need a leader who will say "Make it so!"

If you have a comment or question about lunar water feel free to send a Letter to the Editor.
I can't promise to answer all your questions or address all your comments, but I'll post a few particularly good ones here.

Dr Jamie Love, the editor of this website and all of Science Explained, has written several self-study science courses specifically designed for home schoolers and other distance learners. These courses are "hypertextbooks" - delivered over the internet and read on your computer, just like web pages. To organize and distribute these hypertextbooks, Jamie created Merlin's Academy - a (non-accredited) "virtual school". Merlin's Academy sells self-paced, self-learning hypertextbooks that teach Alchemy (actually, Chemistry ), Astronomy and Genetics in a fun and unique way. Each course has computerized exams, unique features and a style best suited for teaching the subject. Principles of Alchemy (Chemistry) is for younger students (up to highschool), while Principles of Astronomy is for more advanced students (hobbyists & first-year university), and Principles of Genetics is most suitable for very advanced students (at university). However, every student is different and it would not be fair to generalize. So, visit Merlin's Academy where you can learn more about the courses, request free samples of each course (to download onto your computer) and enjoy the free online samples.

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