Stomping on the moon

FULL MOON By michael light Alfred A. Knopf, $50

Photos by astronauts of the Apollo program to commemorate first moon walk.

When Neil Armstrong took "one small step for man" July 20, 1969, he entered a desolate world. If that first moon walk, which he also called "one giant leap for mankind," were ever to lead to an international

moon base, scientists would have to assess the available lunar resources. Possible hidden water supplies top their wish list.

Thirty years later, the Lunar Prospector science team thinks it may be able to prove definitively that water ice does indeed exist in the bitterly cold, permanently shaded parts of craters around the moon's north and south poles.

As the final act of their mission, they plan to send the Prospector spacecraft, now orbiting the moon, crashing into the 30-mile-wide crater Mawson in the south polar zone July 31. Slamming the 650-pound drum-shaped spacecraft into Mawson at nearly 3,800 miles an hour should eject a cloud of debris. The team estimates it could throw some 40 pounds of water vapor high enough above the moon to be seen from Earth.

Team member David Goldstein from the University of Texas at Austin warns that "our proposed experiment is a high-stakes gamble." At a meeting of the American Geophysical Union in Boston in May, he told the press that "there are several ways to fail," including not hitting the target in a way to throw out the expected debris. Moreover, the water vapor will be hard to detect even if it is there. Therefore, he said, a negative result would mean nothing. Only a positive result will have meaning.

Definite proof of water on the moon would cap three decades of discovery. Six Apollo landings and three Russian robotic sample return missions gave scientists 849 pounds of rocks and soil to study. From these and data gathered by orbiting spacecraft, researchers concluded that the moon, like Earth, formed about 4.5 billion years ago.

Comparison of the lunar surface composition with that of Earth supports the "big whack" theory of the moon's origin. This holds that an object the size of Mars or larger knocked off part of the young Earth at that remote time. The moon coalesced from the debris. Volcanism and heavy bombardment by asteroids and meteorites then shaped the lunar surface. The action calmed down some 3 billion years ago.

Findings from the 1960s and 1970s gave scientists an overview of the moon's history and some insight into its surface composition and internal structure. But the data came mostly from the equatorial region.

That changed when the US Department of Defense sent its experimental Clementine satellite into lunar orbit in 1994. It mapped the entire moon. For 98 percent of the surface, its data produced charts accurate to within 500 meters (1,640 feet). What was most intriguing, Clementine radar found signs of water in polar craters. Then, in January 1998, came NASA's Lunar Prospector. Its instruments have mapped 11 key elements such as uranium, manganese, and iron. Gravity and magnetic measurements have confirmed that the moon has a small core containing about 2 percent of its mass.

One key element - hydrogen - shows up strongly in the shaded polar craters. Prospector team member William Feldman from the Los Alamos National Laboratory in New Mexico says, "We really feel very strongly it's a concentration" of hydrogen. It very likely "could be water," he adds, perhaps deposited by comets.

Prospector could prove that point when it ends its mission in a sacrificial crash. Meanwhile, the science team is eyeing some of the earth satellites. When their useful life ends, they may have enough fuel to reach the moon and crash into other craters.

Prospector's mission ends an epoch initiated by Apollo and begins a new era of robotic exploration. This time, the US and Russia are not alone. Japan joined the quest in 1990, when it launched the Hiten lunar orbiter mission. Hiten returned data on space navigation and meteoritic dust before finally crashing on the moon in 1993. That was a test flight. Now, Japan's Institute of Space and Astronautical Science (ISAS) is preparing a scientific follow-up. Called Lunar-A, it includes an orbiting mother ship that would drop two penetrators into the lunar surface. These would probe the interior by measuring heat flow and quakes.

Looking beyond this, planners at ISAS and the National Space and Development Agency have sketched out missions that include surface-roaming robots.

Thirty years ago, American astronauts left behind a plaque: "Here men from the planet Earth first set foot on the moon July 1969. We came in peace for all mankind." Now, more of human-kind wants to join the chorus.