Earth has no business with a moon as large as Luna. Our Moon, in fact, is so large compared to its parent planet that some have considered calling the pair a double planet. Spaceflight between Earth and Moon is similar to interplanetary flight on a greatly reduced scale. The Moon is larger than Pluto, and almost as large as Mercury. It is currently some 240,000 miles away from Earth, but this was not always the case. It is receding at the rate of about 1 in. per year, so that by "running the clock" backward, scientists have deduced that the Moon originated much closer in. Some have even suggested that the Moon was born of our home world, mysteriously ejecting itself out of what is now the Pacific Basin long before the reign of the dinosaurs or the trilobites, or even the first unicellular organisms. They point to the volcanic "rim of fire" that still encircles the Pacific as proof of this thesis. But this is an outmoded idea, borne of the simple-minded notion that current trends - the Moon's incremental retreat - can be time-reversed and extrapolated back to a planetary fission. Using sophisticated computer-generated trajectory and collision analyses, the latest theory of the Moon's origin is that the proto-Earth was struck by a pre-Lunar body roughly the size of Mars early in the formation of the Solar System. This event is supposed to have occurred about 4'/2 billion years ago. The collision of the two planets caused a coagulation and redistribution of mass on a planet-rending scale, completely obliterating the smaller body, while simultaneously throwing into orbit a huge mass of debris that initially became a ring system. The young Earth, fuming molten red from this unexpected turn of events, would have looked like Saturn's little sister. Shortly - in a mere million years or so - the planetary ring system coalesced and became the Moon. This theory explains why the Moon does not orbit in the plane of Earth's equator, and might even help to explain why the Lunar core is so small. The Moon is composed mainly of mantlelike material ejected from the proto-Earth.
What does the Moon have to offer us? As mentioned above, the greatest gift is the potential the Moon has in helping mankind become a spacefaring species. The Moon, for a planet like Earth, provides the perfect base of operations for the future development of a space-based civilization. It promises to give us the sheer experience we will need to become masters of the Solar System, in the same way that Scandinavian geography made the Vikings masters of their northern realm. This is an intangible resource, but a physical one nonetheless, for the Moon is very real and very near. Beyond the practice in spaceflight operations we will gain in going to the Moon, there is also the nitty-gritty stuff that the Moon is actually made of. There are elements in the regolith that do not exist on Earth. There may be large quantities of ice lurking in the polar shadows. There could well be undiscovered caves harboring unsuspected treasures. Imagine finding an alien artifact, a crashed spaceship from some planet beyond the Solar System, or even an alien corpse. For the scientist, the Moon is a natural laboratory. For the geologist, it is a paradise. For the astronomer, the views of the heavens are unhampered. For the radio astronomer, the Lunar far side offers a "quiet" environment free of artificial Earth emissions. And for the biologist, it offers a harsh environment to test the survivability of various organisms. The botanist will practice perfecting plants that can survive - even thrive - through the 2-week-long Lunar night. The rocket scientist will synthesize energetic propellants directly from the Lunar soil, or electrolyze them from local ice deposits. Environmental engineers, too, will derive life-sustaining oxygen from the same sources. And the nuclear engineer will mine the Moon for the rare-Earth element helium-3, to be used as fuel in fusion reactors on the home world. These are just a few of the resources our good satellite has to offer, but we will need good spaceships to get us back and forth.
To sustain spaceflight operations between Moon and Earth, a Lunar source of rocket propellants would be a great boon. There are two obvious sources worth investigating: the polar regions and the ubiquitous regolith, or Lunar soil. The Clementine spacecraft detected evidence for water in 1995 at the Lunar poles. This could be interpreted as evidence for ice deposits in shaded areas where the Sun never shines. And Apollo astronauts brought back samples that reveal the abundance of helium-3, a heavy isotope of helium.2,3
Water, in the form of ice, is abundant in space. This may seem surprising, but it is borne out by the fact that the Solar System is full of icy bodies. The Kuiper Belt, that region inhabited by Pluto and other dim planetoids, might just as well be called the Ice Belt. Further out is the Oort Cloud, the vast repository of the comets. And these are icy bodies as well. Three of the large moons of Jupiter -Europa, Ganymede, and Callisto - have large quantities of ice. Europa is believed to have a liquid water ocean vaster by volume than the seven seas of our own world, permanently hidden beneath an ice crust. And Mars has huge quantities of ice at its poles and beneath its surface. All of this supports the expectation that water ice will be found on Luna as well. NASA's Lunar flight program is concentrating on the polar regions in hopes of finding ice deposits in permanently shaded craters. If such deposits do exist, then it will be possible for astronauts to "live off the land" by mining the Moon for ice. It can then be melted, purified, and used for a host of purposes. Among these are drinking water, rocket propel-lants, and oxygen for life support.
For 4/ billion years, the Moon has been absorbing particles from the Solar wind and imbedding them in the dusty regolith. Among these particles are atoms of helium-3, a specific isotope of that inert element first discovered in the spectrum of the Sun itself. Helium-3 occurs on Earth in tiny quantities only, but it exists in much greater abundance on the Moon. This isotope - or heavy version - of helium may one day power a nuclear fusion technology for the twenty-first century on Earth. And such a civilization would depend on the Moon for its supply of helium-3.
Mining the Lunar regolith for helium-3 could have unexpected benefits that pertain directly to space infrastructure. As this rare-Earth element is refined, several important by-products appear during the process. These include large amounts of hydrogen, as well as methane, carbon dioxide, and water. These compounds, or the elements they contain, are locked in the Lunar soil, and have obvious uses as pro-pellants and life-sustaining substances.4
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