NASA has not only been working at making its spacecraft for exploring other worlds "faster-better-cheaper," it has been showing a new kind of creativity. Back in July, the agency had squeezed just about everything it could out of one of its new breed of stripped-down instrument platforms. The Lunar Prospector had spent 19 months in a polar orbit around the moon, gathering information on its gravitational and magnetic fields and surface composition (until now most measurements had been made near the moon's equator).
The 354-pound spacecraft was reaching the end of its useful life. Nearly all the fuel used for maintaining the craft's orbit was gone. Perhaps, too, the thought of simply leaving the Prospector to crash unremarked into the moon offended people's sense of neatness or completeness. In any event, a team of scientists led by David Goldstein, of the University of Texas, had an idea. Some astronomers — including Goldstein — had speculated that there just might be water ice mixed in the soil at the bottoms of craters at the moon's poles, places where sunlight never penetrates. The ice would never have melted, frozen forever by temperatures as low as -280 degrees F.
There was more. The Lunar Prospector had found evidence for the existence of hydrogen at the poles, a signal that itself could have meant water ice was present. How to find out? Goldstein's team proposed deliberately crashing the Prospector into a polar crater and analyzing the resulting impact debris. NASA agreed in a remarkably short time, a crater was picked and calculations made. The Hubble Space Telescope and major observatories on the ground, including the Keck in Hawaii and the McDonald in Texas, would watch for a plume of debris.
NASA last talked to the Lunar Prospector in the early morning hours of July 31, instructing the spacecraft to fire its thrusters in such a way that it would slam into the moon in the chosen crater. It was programmed to come in at a low angle over the rim on one side of the crater, traveling at 3,800 miles per hour, and crash at the base of the other side at 5:52 a.m., Eastern Daylight Time. They guessed the resulting cloud of debris could contain as much as five gallons of water. The Prospector disappeared behind the moon, as it had done more than 6,800 times before. It never reemerged, so NASA assumes it crashed as planned. No one saw a debris plume. Astronomers were still analyzing the data as this column was written. NASA had no way of knowing for sure where the Prospector crashed. Future explorers will finish the story.
It was a creative idea, though, trying to get one more bit of information out of a piece of dying hardware. (What a bit of information it would have been! If there is water on the moon, it will be infinitely easier for people to live there, should that time come.)
NASA has more ideas about slamming things into celestial objects to see what they're made of. A team of astronomers led by Michael A'Hearn at the University of Maryland proposes to "shoot" a comet. In the original plan, a spacecraft would rendezvous with Comet Tempel 1, believed to be about four miles across, in 2005. It would fire a 1,100-pound copper "impactor" at 22,400 miles per hour into the sunlit side of the comet, making a crater predicted to be larger across than a football field and 80 feet deep. The depth is critical. The scientists hope to find out not only what the surface is composed of but also what lies inside. (The bullet is made of copper so that when it vaporizes on impact, its presence will not confuse the results. Copper is not believed to be a constituent of this type of comet.)
Instruments aboard the spacecraft would record what happens at both visual and infrared wavelengths. A high-resolution camera would provide detailed images while one with medium resolution would offer a view of the whole crater and the comet nucleus. Once again space and earthbound telescopes would be watching. The comet would appear to momentarily brighten. (The whole scenario is iffy because at the end of July, the House Appropriations Committee cut the funds for Deep Impact and other space-science missions.)
If and when Deep Impact goes forward, the world's oldest science will have added a new department. You could call it high-impact astronomy, but an even better name might be experimental astronomy, something until now considered impossible.
Amid the violence of this new branch of astronomy, there has also occurred an entirely different kind of accomplishment. The Lunar Prospector did something far grander than study the moon for all those orbits and then use its last gasp to try to discover if there is water ice deep in polar craters. It carried the remains of a human being, in the form of ashes, which crashed with it on the moon, the first person to come to rest on a celestial body other than earth. Nowadays when a baseball player hits a home run, broadcasters sometimes say: "[Jones] has left the building." It's fun. But a man named Eugene Shoemaker really has left the planet.
The late Krafft A. Ehricke, a rocket designer, proposed that the most important events in the history of earth occurred when plants started to metabolize sunlight and when human beings began to metabolize information. The third, he wrote in 1985, would happen when human beings evaded the restrictions of living on a finite world by colonizing other worlds. This "extraterrestrial imperative" was crucial, he believed, and would happen in three steps: space industrialization, space urbanization and, finally, "extraterrestrialization," a mouthful meaning the inevitable divergence of people living on the moon, Mars and other planets and moons. In a symbolic way, in the form of one man's ashes, the migration has begun.
Shoemaker was a geologist who worked for the U.S. Geological Survey most of his life. He almost single-handedly founded the field of astrogeology, starting when scientists could not agree on whether most of the moon's craters resulted from impacts or volcanism. By showing conclusively that the 4,000-foot-wide crater near Winslow, Arizona, was formed by the impact of a meteorite, he catapulted forward the study of lunar craters. (Most are now believed to be the result of impacts.) The hole in the ground in Arizona is today known as Meteor Crater.
Shoemaker was interested in anything that could hit a planet or a moon. He surveyed the near-earth objects. In the process, he and his wife, Carolyn, discovered a number of comets, including the fragmented one named for them and David Levy that crashed into Jupiter in 1994 (Smithsonian, June 1994 and January 1995). He died in 1997 in an automobile accident in Australia, where he was — what else? — studying impact craters.
He was unassuming, easygoing, smiling in conversation. At science meetings, he was infinitely patient with the press. From the first time he answered my questions at meetings of the American Association for the Advancement of Science in the 1960s to the last time at the Seattle meeting in 1997, he made me feel more at ease in my ignorance than almost any other scientist I've ever met. I hardly knew the man, but when he died, I felt I had lost a friend. I had. We all had.
More than anything else, he had wanted to go to the moon but a medical problem kept him out of the astronaut corps. Now he's there. For all those people all over the world who have ever wanted to trudge those gray sands and look back at the earth, but will never be astronauts, it's nice to know that one of us made it.