A lunar geologist would have to know something about the holes on the moon. In the late 1940s, prevailing opinion said that these holes had been made by volcanoes. Gene taught himself explosive volcanism. The earth’s surface concealed many enormous, ringlike features known as crypto-volcanic structures—believed to be the remains of superexplosive volcanic eruptions. He studied cryptovolcanoes. He also walked around Meteor Crater, a hole in the ground nearly a mile across, outside Flagstaff. Despite its name, “the majority of geologists,” Gene said, “were equivocal—skeptical, perhaps—that it was of impact origin.” Some thought that Meteor Crater might be a collapsed salt dome or a hole left by a volcanic steam explosion. Not many professional geologists accepted a theory first proposed by Daniel Moreau Barringer in 1906, that a nickel-iron meteorite had exploded on impact there. Gene set out to make a geologic map of Meteor Crater for his Ph.D. thesis. Barringer had drilled a series of holes in the floor of the crater, hoping to find a nickel-iron asteroid under the crater, which he never found. Gene examined Barringer’s old core samples and discovered they contained a lot of shattered rock, which was full of microscopic droplets of quartz glass saturated with particles of meteoritic iron. Around the lip of the crater Gene found layers of sedimentary rock peeled back from the rim, “like the petals of a flower blossoming.” He discovered that these layers of ejected rock had been deposited in reverse order. No volcano would lay down ejected debris in such an orderly fashion. For comparison he mapped craters formed by nuclear bombs in the Nevada desert—the Jangle U crater and the Teapot Ess. There he found thumb-sized blebs of shock-melted glasses blown into deeply shattered rocks, and sediments peeled back like flower petals from the lip of the crater, laid down in reverse order. The resemblance between nuclear and meteor craters seemed eerie to him. The evidence came to this: Meteor Crater had been made by an asteroid.
He stayed with the Geological Survey after receiving his degree. In 1960, Gene, Edward Chao, and Beth Madsen, all of the Geological Survey, discovered a natural mineral that they named coesite, found in the rocks of Meteor Crater. Coesite is a polymorph of silica that can form under shock—a wave of extreme pressure must rip through the rock, crushing the silica’s molecular lattice into coesite. No known event at the surface of the earth other than the impact of a giant meteorite could do that. As Gene would later say, “We had discovered a fingerprint for impact.” That brought him to Germany.
The Ries Basin is a circular depression seventeen miles across, north of the city of Augsburg, on the western border of Bavaria. Most geologists had assumed it to be an old volcano. “My German wasn’t good,” Gene said, “but the more I read about the Ries Basin, the more I became convinced it was an impact crater.” He believed that with the coesite fingerprint test he could prove it. On July 27, 1960—six days after the discovery of coesite was first published—he and Carolyn drove into the Ries in a new Volkswagen bus. Around sunset they found a quarry—it belonged to a cement factory, and the workers had gone home—and climbed down inside. Gene broke a few pieces of rock with his hammer and looked at them in the fading light. At that moment, a scientific field, impact geology, came of age.
“The rock was shocked, melted, crushed,” he said, “full of blobs of dark glass. I just knew instantly there was coesite in it.” During the following days Gene and Carolyn explored the Ries. Gene walked through villages in a daze, with a rock hammer dangling from his hand. He found blasted, shocked rock everywhere, even cut into blocks and built into walls and houses. The Ries was a tremendous impact crater, populated with farms and towns. Near the center of the Ries they came across St. George’s Church, in the town of Nördlingen, built of the Ries rock—a shattered and sintered granite speckled with oozy droplets of black glass. The medieval stonecutters had unknowingly put up a church to the God of the Apocalypse. Fifteen million years ago, during Miocene times, something had come in from space and exploded on impact. Crustal rocks had offered this object the resistance that a tub of lard would give to a concussion grenade. Rock blown from the lip of the Ries Basin had soared or slithered for miles across Bavaria. The Ries amounted to a Kepler or a Tycho—essentially a lunar crater in Europe.
That was the first proof that a giant impact crater existed on the earth. Gene’s discovery opened the question of just how many impact craters the earth conceals, and it also opened the question of whether many of the so-called crypto-volcanic structures might actually be the eroded roots of impact craters. At last count, geologists have identified more than one hundred likely impact structures, including the sacred Lake Bosumtwi in Ghana; Lake Manicouagan in Quebec; dozens of eroded craters in the United States, including structures called Crooked Creek, Decaturville, Flynn Creek, Upheaval Dome, and the Manson Structure; the Serra de Cangalha in Brazil; the Rouchechouart in France; and Gosses Bluff in Australia. Gene thinks that perhaps as many as a thousand impact craters will eventually turn up, “provided we don’t cover the earth with nuclear craters first.” In 1960, when he walked into the Ries, the debate over whether the moon craters had been made by volcanoes still lingered; but if a big impact crater could be found on the earth, then those holes and rings in the moon would be impact craters too. Galileo had seen them the first time he looked through a telescope, but to show that they were made by asteroids and comets, and that the earth was pockmarked with similar rings, took three more centuries and Gene Shoemaker with a hammer.
He founded the United States Geological Survey’s Branch of Astrogeology, now located in Flagstaff, dedicated to the geologic study of other worlds. He grew to prominence in the American space program, working first on the Ranger lunar probes, then as Principal Investigator for the imaging cameras on the Surveyor lunar lander, and finally as the Principal Investigator in charge of the geological fieldwork done during the Apollo manned lunar landings. But he never achieved escape velocity; he never left the earth. The adrenal glands on his kidneys progressively failed in 1962, killing forever his chances of going into space. “The irony of it,” he said, “is that I chaired the committee that recommended the names of the first astronaut candidates to NASA.” He would never forget the night launch of Apollo 17—the last of the manned lunar missions. He and Carolyn watched enthralled at Cape Canaveral as their friend and colleague from the Geological Survey, the geologist Harrison H. Schmitt, pulled away from the earth riding on a Saturn V rocket, which brightened and dimmed as it cut through cloud decks, a machine as tall as a thirty-story office building and already going at supersonic speed as it leaned to begin its roll downrange, while Gene studied, with the detachment of a scientist, the pain of the unfulfilled hope that had started that summer in 1948, in Paradox Valley, and which had delivered him to an open field in Florida, witnessing the launch of the first and last geologist to walk on the moon.
He would eventually leave the Apollo space program for other things, but he could not keep his eyes on the ground. Ever since Meteor Crater and the Ries, he had been wondering about rocks that fall from the sky. How many of them are out there? If you went looking for them with a telescope, what would you find? Could finding rocks in space give you a better estimate of how often the earth takes a hit? In 1972, when he began seriously thinking about a program to search for earth-crossing asteroids, the orbits of only three earth-crossers were accurately known: Icarus, Geographos, and Toro. Apollo had been lost. Hermes, the asteroid that had ambushed the earth in 1937, had also been lost (it still is). Astronomers had shown more interest in looking for exploding galaxies than loose cannonballs near the earth. Yet the bombardment of the earth was quite obviously a continuing natural process.
He began working with a geophysicist from Caltech’s Jet Propulsion Laboratory, Eleanor Helin. Like Gene, Eleanor had begun to suspect that the number of earth-crossers might be enormous. She probed the Caltech archives looking for sightings of lost minor planets. She traveled to Germany to decipher the logbooks of dead astronomers—of Max Wolf and Karl Reinmuth—trying to recover the orbits of vanished earth-cro
ssers. In 1973, Shoemaker and Helin founded the Palomar Planet-Crossing Asteroid Survey. She carried on the bulk of the telescopic work during the program’s early years, spending long nights on the eighteen-inch and the forty-eight-inch Schmidt telescopes on Palomar. They endured gambler’s luck. Right at the beginning, a huge Apollo object swept by, 1973 NA, now lost. “I said, ‘Hot damn! We are on to something!’ ” Gene recalled. But then came a long dry spell with no discoveries. Then a burst of discoveries. Then another dry spell. “There were times when I was almost ready to give it up, but Eleanor Helin just would not quit.”
She discovered Aten and Aristaeus, and codiscovered Ra-Shalom, all earth-crossers. She also discovered a large number of asteroids known as Amors, on unstable orbits near Mars—objects that could either hit Mars or be flipped into earth-crossing orbits in the future. Shoemaker and Helin defined three classes of earth-crossers. The Aten objects spend most of their time inside the earth’s orbit. The Amor objects spend most of their time out around Mars, moving inward to brush the earth’s orbit once in a while. The Apollo objects slash deeply back and forth. Gene has estimated that there are a total of about two thousand big Apollos, Atens, and Amors out there—asteroids able to collide with the earth now or at some time in the future—two thousand drunken mountains driving the freeways, most of which we have never seen. Smaller objects—the size of the Great Pyramid at Giza, for example—are exceedingly more numerous but exceedingly difficult to find. The odds are slim that something large might hit the earth during a human lifetime. From the human perspective, major impacts are rare. “Human civilization,” Gene said, “is essentially instantaneous.” From an astronomical perspective, hypervelocity planetoids slam into the earth rather frequently. We live in an asteroid swarm.
Shoemaker and Helin eventually decided to divide their program. Helin founded the International Near-Earth Asteroid Survey—a program to coordinate sightings of earth-crossers all over the world. Shoemaker opted for a small but intense program on the Little Eye. Having neither the time nor the patience to scan films for asteroids, he needed an assistant.
It had not taken Gene long to propose marriage to Carolyn, but after they had been married, it had taken Gene about two years to work up his courage to tell her that he intended to go to the moon. She was frightened. She wondered if her husband was unstable. On second thought, that did not seem too bad, considering that she had always wanted to go to the moon herself, since those summer nights in Chico during her childhood; and so their hope became a mutual affair. She would explain that during the 1960s, “I thought that travel to the moon would become so common that even someone like me would be able to go.” Neither of them had made it into space, but at least there was no harm in going up on a mountain each moonless part of the month between September and May, to photograph a dome of jewels out of reach and to swear at a telescope.
The eighteen-inch Palomar Schmidt telescope was a wide-field telescope; it yielded virtually a panoramic view. In one snapshot the Little Eye could photograph an area of sky larger than the bowl of the Big Dipper. The Little Eye contained two pieces of glass—a twenty-six-inch mirror and an eighteen-inch corrector glass at the nose. (Schmidt telescopes are rated in size according to the diameter of the corrector glass, not the mirror.) The Little Eye was one of the smallest professional telescopes in use anywhere in the world, and it bulldozed the sky. The Hale Telescope, on the other hand, drilled thin holes into lookback time. Even using electronic cameras, the Hale Telescope would require more than a human lifetime to make an overlapping mosaic of pictures of the northern sky. The Little Eye surveyed the entire northern sky more than once a year. The Big Eye had never caught an unknown asteroid cruising near the earth. “The eighteen-inch,” Gene said, “is the fastest gun in the west.” He felt, however, that small telescopes did not attract government funding or the attention of private donors. The Shoemakers’ search for asteroids that could hit the earth was costing six thousand dollars a year. That was apart from Gene’s salary, which the Geological Survey covered when he was on the mountain. Much of the six grand went to pay for rolls of film. “The cookies,” Gene said, “are two dollars a throw.” The Shoemakers had been trying to raise some grant money to cover a salary for Carolyn, without luck. The Geological Survey would have been happy to cover her salary, but federal rules on nepotism prevented that. She had no choice but to value her time at nothing. She found earth-crossers for free. Gene said, “We’re getting too much of a bang for these bucks.” Dents on the Little Eye’s tube suggested that it had been getting more bangs than bucks for a long time.
Bernhard Schmidt, the inventor of the Schmidt telescope, was born in 1879 on an island off the coast of Estonia called Nais Saar, which means The Island of Women—a whaleback of fields and forests in the Baltic Sea, five miles long, with a lighthouse at one end. The islanders dressed in the old costume and took their Lutheran religion seriously. Bernhard was a troublesome boy with a scientific bent who took bombs seriously, and he began designing and building them for fun. One Sunday morning, at the age of eleven, he skipped church and went into the fields to set off a pipe bomb of his own design. The material inside the pipe detonated unexpectedly, yielding a blast that must have rattled the windows of every church on Nais Saar. The blast also took off the sleeve of his Sunday suit, which unluckily had contained his right arm, which was also gone. He washed the bloody stump in a brook and waited in the woods for the churches to let out, and then ran home, afraid he would be punished for drenching his suit with blood.
After losing his arm, Bernhard Schmidt turned to the science of light. He began to grind lenses as a hobby, and when he grew up, he left the Island of Women. Around the turn of the century Schmidt landed in the town of Mittweida, in Germany. There he set up a workshop in an abandoned bowling alley, where he ground mirrors for amateur astronomers and lived on the small amounts of money that he got for his polished glass.
The difficulty in making astronomical mirrors lies in grinding a concave surface that will gather starlight and bring it into sharp focus. An astronomical mirror is a light scoop designed to pour a large quantity of light into a tiny area, and the wider and deeper the scoop, the more light it can deliver rapidly to the film. In the language of optics, a mirror that can gather faint light quickly is said to be a “fast” mirror. The use of a fast mirror allows for brief exposures on film, thereby speeding up the astronomer’s work. A fast mirror is a steeply curved mirror. The curve known as a paraboloid is particularly good at gathering faint light, except that parabolic mirrors suffer from an unavoidable optical defect: only a tiny area at the center of a photograph taken with a parabolic mirror contains stars in good focus. Toward the edge of the photograph, the stars smear into commas. Astronomers avoid this defect by restricting the size of the film to a small area in the center of the field of view. In the Hale Telescope, for example, the area of good focus is about three-eighths of an inch square at the focal plane—an area the size of one’s little fingernail. Parabolic mirrors are terrible for searching large areas of sky.
Bernhard Schmidt became a master at shaping fast parabolic mirrors with his left hand. He kept himself going on brandy, cigars, coffee, and sweet cakes. With a fishtail of cigar stuck to his lip, Schmidt paced over his mirrors in the bowling alley all night, touching them a little with a polishing tool held in his left hand, keeping his empty right sleeve pinned up to prevent it from dragging on the glass. To get into the bowling alley he had to walk through the Lindengarten Restaurant. He told the proprietress, Frau Bretschneider, “Put out a good bottle of brandy for me, and if as I go by I pour myself some, then I’ll make a mark on the beer mat.” Schmidt kept his telescopes in an empty lot across the street from the Lindengarten Restaurant. On cold winter nights, when he was observing stars and simultaneously polishing glass, he kept rushing back and forth through the Lindengarten Restaurant, each time having a shot of brandy. The brandy got Schmidt coming and going, and by the end of a night the beer mat was covered with
marks. “We used to make out very well with him,” Frau Bretschneider remembered.
Schmidt’s telescopes appeared to be screwed together out of scrap lumber and vegetable crates. One of them, a solar telescope, had a heliostat mirror that tracked the sun by means of a dripping water clock. He was shy and aloof; he never married. There is no evidence that he liked women. He may have been homosexual, except that there is no evidence that he liked anybody, much. He was a frank pacifist. “Only one man alone is worth anything,” Schmidt once said. “Put two men together and they quarrel. A hundred of them make a rabble, and if there are a thousand or more, they’ll start a war.” So they did, in 1914. The German police began to watch him. They had no idea what was going on with the mirrors and the water clock, but they knew he was a pacifist, and since he was an Estonian, they concluded that he was an Estonian traitor flashing signals to Russian aircraft. They put him in a prison camp, where he suffered terribly. When the war ended, he returned to his bowling alley to continue grinding lenses.
In the years following the First World War, Schmidt’s work came to the attention of professional astronomers in Germany. Professor Richard Schorr, director of the Hamburg Observatory, at the risk of getting himself into trouble with the police, managed to extract Schmidt from his bowling alley and install him in a single-men’s dormitory at the observatory’s branch in the town of Bergedorf, outside Hamburg. There Schmidt lived for the rest of his life, a volunteer member of the staff and a chronic alcoholic, making mirrors for the observatory whenever he felt like it. They called him der Optiker B. Schmidt—The Optician B. Schmidt.
First Light: The Search for the Edge of the Universe Page 13