Another giant leap

As if to tantalize researchers further, some scientists have posited that because the lunar surface is essentially pristine compared with Earth's, and because meteorites from Mars have been found on Earth, it may be possible to find relics from other inner planets strewn across the lunar surface.

Some 4 billion years ago, astronomers say, the inner planets endured what has become known as the Late Heavy Bombardment, which lasted roughly 200 million years. During this period, Earth, our moon, and other inner planets would have exchanged material as they took direct hits from asteroids or encountered collision debris from objects striking their inner-solar system counterparts.

On average, these planetary shards could amount to more than 22 tons of terrestrial material spread over each 38-square mile patch of lunar surface, estimates John Armstrong, a research professor at Weber State University in Ogden, Utah. More distant planets would have progressively less representation.

Other researchers calculate that the amount of material, if it exists at all, would be much less. Still, Dr. Armstrong suggests that these cosmic shards on the moonscape - particularly those from Earth - may yield unique clues to Earth's first billion years and perhaps hold geochemical evidence of early life.

Yet even as planetary scientists look forward to new opportunities to study

humankind's surrogate for other planets, others are looking long-term at commercial opportunities - ranging from supplying companies with data about the moon to building manufacturing

plants and power plants on the lunar surface.

Dr. Binder, who heads the nonprofit Lunar Research Institute and the for-profit Lunar Exploration, Inc., sees scientific gains and a great deal of money to be made from future lunar activities. In the short term, robotic exploration makes sense, he says. And the use of the moon as a place to learn to "live off the land" for future planetary exploration is also a logical approach.

Scientists and engineers have been devising ways to beam energy from solar-cell installations on the moon via microwaves to Earth. Former Apollo 17 astronaut Harrison Schmitt has been working with fusion-energy researchers at the University of Wisconsin who are devising reactors that use a heavy isotope of helium as fuel. The isotope is abundant on the moon.

There is also indirect evidence of possible water in the moon's polar craters. The Clementine and Lunar Prospector spacecraft detected large amounts of hydrogen there. Binder and others hold that if water is present, it's likely to be bound to dust grains as small particles, rather than blocks of ice. Yet even if water is not present, he says, the hydrogen can be "mined" and combined with oxygen - abundant in lunar minerals and soil - to make water.

The two mapping missions in the 1990s revealed deposits of other materials - such as silica, iron, titanium, magnesium, and aluminum. These could be used for a range of products manufactured on location.

"We have the raw materials for a civilization" to build the structures it needs on the moon, Binder says.

Beyond Earth's orbit

Here are some key flybys and landings in 40 years of space exploration:

Mercury: Mariner 10 flew past the planet in 1974-75 and shot photos of 45 percent of its surface.

Venus: Russian landings and Pioneer flybys in the mid to late '70s examined its sulfuric-acid rain and carbon-dioxide atmosphere. The Magellan mission in 1989-90 produced detailed maps of Venus.

The moon: Six Apollo landings from 1969 to 1972 represent the first - and only - times man has walked a surface beyond Earth.

Mars: Three decades before today's rovers, a Viking landing in 1976 helped scientists better understand the planet with photos of possible ancient rivers and lake beds.

Jupiter, Saturn, Uranus, Neptune: Launched in 1977, Voyager 1 and 2 flew by all four planets, as well as their rings, moons, and magnetic environments.

SOURCES: NASA, The Planetary Society

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