“When I married Gene,” Carolyn said, under the telescope, “the one thing that I hadn’t quite figured on was what a workaholic he is.”
“Ha, ha! Carolyn’s pretty competitive herself,” Gene said from the control desk.
“What’s my time, Gene?”
“You have forty-five seconds.”
She had tried teaching junior high school, hated it, and had gotten pregnant just in time to save herself from feral ninth-graders. “I spent many years having a family,” she said. “I enjoyed that. But I found I could get pretty restless. Then I sort of eased into minor planets. Once you start finding them, it’s so much fun that you can’t stop.”
“Ten seconds …”
“Now I really cannot stop finding them.”
“Five …”
“Sometimes I so much do wish I could stop finding them.”
“Close.” Gene said the word quietly, with an unmistakable satisfaction at another capture of photons.
Carolyn Shoemaker was a watcher on the masthead, and she let out the first cry when an asteroid or comet came over the horizon. She could tell from an object’s motion if it was something unusual. She would report such things immediately to an astronomer named Brian Marsden, who is the director of the Minor Planet Center in Cambridge, Massachusetts. Marsden would calculate the object’s orbit on a computer. If the object turned out to be an earth-approaching asteroid, the Minor Planet Center would send out an international announcement of the discovery, thereby enabling other astronomers to perform detailed studies of the object as it passed by the earth. Carolyn had discovered (in addition to six comets) six earth-crossing or earth-approaching asteroids—1983 RB, 1984 KB, 1984 KD, 1985 TB, Nefertiti, and Mera (“a nymph, one of the lovers of Jupiter”). She had found these asteroids so recently that four of them had yet to be named. She had also discovered asteroids of various other classes (asteroids are often classified according to their types of orbits). She had discovered ten asteroids in the Hungaria class and fourteen in the Phocaea class. She had discovered the Trojan planet Paris, and also a giant asteroid out near Jupiter that she and Gene had named Caltech. She had also reported sightings of more than three hundred nameless Main Belt asteroids. She had, however, discovered and named quite a few Main Belt asteroids. Although these were not dramatic asteroids, like earth-crossers, they were perfectly decent minor planets, suitable for naming. One Christmas Eve, she and Gene put framed photographs of star fields under the Christmas tree. Each photograph displayed a streak traced by a moving asteroid. Gene and Carolyn had named several asteroids for their children and other family members.
“I was just blown away,” said their son-in-law, Fred Salazar, who received a minor planet permanently named Salazar, with the blessing of the International Astronomical Union, which oversees the naming of celestial objects. Fred’s wife, Linda (who is Gene and Carolyn’s youngest daughter), got the planet Linda Susan. Gene’s mother got the planet Muriel. Gene and Carolyn’s daughter Christy got Christy Carol, and their son, Patrick Gene, got Patrick Gene. Patrick’s wife, Paula Kempchinsky, got the minor planet Kempchinsky. One of Paula’s friends said to her, “My mom never gave me a planet for Christmas. All I get are pillowcases.”
In 1801, Giuseppe Piazzi, a Sicilian astronomer, discovered a small planet in the empty region between Mars and Jupiter. Astronomers were not surprised. A wide gap between the orbits of Mars and Jupiter had intimated that that region might hold a planet. Piazzi named his planet Ceres Ferdinandea, in honor of King Ferdinand III of Sicily, which shocked other astronomers, because they felt that planets should be named after gods. So they shortened the name to Ceres. The next year, Heinrich Olbers discovered a second planet in the same area. He named it Pallas, for the goddess of wisdom. By 1807, Juno and Vesta had been found. Astronomers called these planets “asteroids,” Greek for “starlike,” because they were just points of light in a telescope. Many years went by without a new planet. In 1845, a postmaster named Hencke found the fifth asteroid, Astraea, thereby earning himself a pension from the king of Prussia. The land rush began. Before long, minor planets were turning up at the rate of five a year. One celebrated discoverer of asteroids was a German painter living in Paris named Goldschmidt, who had an apartment above the Café Procope. Goldschmidt aimed his telescopes out the apartment window at night. He bagged fourteen planets.
A tradition of naming asteroids for goddesses was soon firmly established, but by the time that astronomers got to Dynamene and Gerda the daughter of Gimer, they realized that they were running out of goddesses. They began naming planets after their wives, daughters, and female friends—Bertha, Edna, Rosa, Henrietta, Alice. During the 1890s, photography increased the discovery rate of asteroids to twenty a year, and the names veered away from the ladies. A Boston minister discovered Winchester, an exclusive suburb of Boston, in the Main Belt. An Austrian named a planet the Philagoria, for his Vienna club. Karl Reinmuth, the discoverer of Apollo and Hermes, also found Azalea, Geranium, Petunia, Chicago, California, and Granule (this last planet he named to honor the pathologist Edward Gall, who discovered Gall’s Granule, a microscopic body inside white blood cells). A Russian discovered and named America. A Russian discovered and named Mark Twain. Russians also found Gogol, Chekhov, Jack London, and Rockwell Kent, not to mention Laputa, named after the floating island full of mad coprophilic scientists in Gulliver’s Travels; but when they named a planet Karl Marx, that caused an international flap, although nobody seemed to mind when the Americans named a planet The NORC to honor a computer.
Clyde Tombaugh, of the Lowell Observatory in Flagstaff, discovered the planet Pluto in 1930. It is said that he found the ninth planet. This is an understatement—he discovered the 1, 164th planet. Today, about 6,300 planets have numbers and known orbits. Another 65,800 planets have been seen once or twice, not often enough to have their orbits plotted with certainty and thus to be eligible for numbering. Newly numbered minor planets range in size anywhere from a few hundred yards across to a couple of miles across—or in the case of Trojans, fifty to eighty miles across. An explorer of the Main Belt named Edward Bowell is numbering a minor planet once every couple of weeks—using Clyde Tombaugh’s Pluto telescope. Bowell said, “I am constantly up against the problem of what to name these things.” He named a planet Barks, after his favorite comic-book illustrator, Carl Barks, who once sent Uncle Scrooge and the three little ducks on a voyage through the asteroid belt.
An asteroid is not nameable until its orbit is established, which requires three sightings on three separate trips around the sun. Then the asteroid receives a number and becomes eligible for naming. Asteroids are named according to the wish of the discoverer, provided that the name does not offend the International Astronomical Union. Up there (or down there, underfoot) drift the planets Kansas, Libya, Ohio, Pittsburghia, Atlantis, Utopia, Transylvania, and Paradise, the latter photographed for the first time by Schelte J. (“Bobby”) Bus on the thirteenth of February 1977, on Palomar Mountain, and named after the town of Paradise, California, where his parents live. For as long as interest in the Main Belt lasts, the names Michelle, Davida, Douglas, Jerome, Dorothea, Anna, Iva, Diana, Mimi, Mildred, Dolores, Priscilla, Birgit, Oliver, and Iolanda will grace the lips of asteroid specialists. Dr. Paul Wild, of Switzerland, discovered the planet Rumpelstilz. Dr. Wild discovered Swissair, which he named for his favorite airline. He found Ragazza (“the Italian word for girl,” as he explained in Minor Planet Circular No. 4,146, the international announcement of his discovery); Retsina (“in honor of the resined wine of Greece”); Cosícosí (“the Italian characterization of indifference”); and Bistro (“a small, cozy restaurant”). Three planets are named for Eva Peron: Evita, Descamisada, and Fanatica. Somewhere between Mars and Jupiter float the worlds of Fanny, Piccolo, Wu, Photographica, Requiem, O’Higgins, Lucifer, Tolkien, Echo, Zulu, d’Hotel, Fantasia, Limpopo, Valentine, Ultrajectum, Panacea, Geisha, Beethoven, Academia, Dudu, Felix, Bach, Chaucer, Einstein, Dali, Scabiosa, Nemo,
and Mr. Spock.
How these pieces of rock came into being is an interesting story. About 4,550 million years ago, inside an arm of the Milky Way, a star exploded in a supernova. A supernova is the hecatomb of a star. There are at least two kinds of supernovas. One variety (Type II) begins with an aging giant star—a star at least eight times as massive as the sun. As the star grows old, it uses up its nuclear fuel while manufacturing elements. All of the lighter elements in the periodic table up to iron were probably created inside giant stars during late stages of nuclear burning, except for hydrogen, helium, and some lithium, which are primordial elements that were formed during the Big Bang. A giant star burns helium in its core during the last half million years of its life, creating carbon. It burns carbon for six hundred years, creating neon. It burns neon and oxygen to make sulfur, for about six months. The star develops onion layers of elements, all burning and fusing into heavier elements. At the center of the star grows an iron core, surrounded by a mantle of silicon. The iron cannot undergo nuclear fusion; it cannot burn. During the last day of the star’s life, silicon at the boundary between the silicon mantle and the iron core burns rapidly. The silicon fuses into iron, which accumulates around the iron core. The iron core becomes too heavy to support itself. In a hundredth of a second the center of the core collapses. It implodes into a tiny ball of neutrons about the size of an asteroid—a neutron star. The onion-layered star is now a hollow shell. During the next three thousandths of a second the neutron star shrinks and rebounds. It snaps. That snap generates a shock wave that takes about a day to work its way up through the onion layers of the star, eventually blowing the star to kingdom come, generating a flash of light that can outshine a galaxy. The shock wave also ignites rapid nuclear synthesis in the fireball, yielding all the elements heavier than iron, such as silver, gold, and platinum, which join the star’s other materials in a journey outward in a billowing bubble of gas and dust. A gold wedding ring begins with the death of a star. Everything in the human body except hydrogen comes from stars—carbon, oxygen, nitrogen in proteins, potassium and calcium in bone, iron in hemoglobin. Plato was right: humanity originated in the stars.
Shortly before 4,550 million years ago, a certain nameless star exploded in a supernova. The expanding shock bubble drove through a cloud of gas and dust inside an arm of the Milky Way and seeded the cloud with metals, while compressing parts of the cloud. At places along the leading edge of the shock wave, the cloud started to collapse under gravitation. In one place a knot of gas and dust flattened and began to spin. It happens that one of physical matter’s more common habits on an astronomical scale is to collect into a rotating pancake of matter known as an accretion disk. The solar system began as an accretion disk. When the pressure and density at the center of the disk rose beyond a critical level, thermonuclear ignition occurred and the sun was born. The pancake flattened into a disk made of ice balls and rock balls. Called planetesimals, these were the ancestors of planets. The planetesimals collided and stuck together under mutual gravity, growing into planets. As the planetesimals orbited the sun, they separated into rings that probably looked like the rings around Saturn. Jupiter probably condensed first, from a thick ring, followed by the other planets, including the earth. When the planets fattened, their accretion rates slowed. They ate up their available planetesimals until only a few planetesimals were left.
Some planetesimals took their sweet time coming home. Gene Shoemaker’s studies of the cratering rate of the moon showed that even about one billion years after the formation of the earth and the moon, late-arriving planetesimals still continued to pound into the moon, their impacts creating the lunar maria—seas of lava that welled up like blood from wounds on the moon’s face. The earth must have suffered the same late heavy bombardment, and the earth must have once exhibited huge scars from impacts of late-arriving planetesimals, although weather erased these marks long ago. The late heavy bombardment has dwindled to almost nothing today. Almost. In Gene’s words: “The last stage of accretion is still going on.” The planets have never quite left off growing. The earth is now gaining about twenty tons a day, through a continual rain of dust from space. Every once in a while the earth gains two billion tons in one second.
Astronomers used to think that the asteroid belt might be the rubble of an exploded planet. Now they think it is the leftover material from a planet that never formed. Jupiter, the heaviest planet in the solar system, disturbed a ring of planetesimals in the region now occupied by the asteroids, preventing that ring from accreting into a planet. Jupiter’s gravity raked those planetesimals, mixed them up, tossed them around. They could not stick together. Every time two planetesimals collided, they broke into fragments, and Jupiter pulled the fragments everywhere, causing more collisions and the production of more fragments. The asteroids are shattered bits of planetesimals that never congealed into a world; they are the bones of an accretion disk. Jupiter is still churning the Main Belt; accidents still happen. Most asteroids appear to be pieces of broken objects. Hammered by repeated impacts, asteroids are covered with a layer of dust and rubble, and some may even be piles of bashed fragments barely clinging together under their own gravity. Jupiter has already thrown most of the mass of the asteroid belt off into deep space. “If you took all the asteroids in the Main Belt and wadded them up into a ball,” Gene said, “you would get something about a tenth of the mass of the moon. A spit in the bucket.” Jupiter is still gradually grinding up the Main Belt and throwing its fragments away.
While most Belt asteroids are on stable orbits that do not come near the earth, it seems pretty clear to scientists who trace the entanglements of orbits that the Belt must be pumping asteroids into earth-crossing orbits. The Main Belt is itself gathered into rings, separated by clear lanes called the Kirkwood Gaps. Jupiter sweeps those lanes clean. Any fragment that falls by chance into a Kirkwood Gap enters a resonating dance with Jupiter, which can flip the asteroid away. Nothing can remain for long inside a Kirkwood Gap. Orbital specialists believe that the Kirkwood Gaps, and other unstable areas in and around the Main Belt, are a source of many earth-crossing asteroids. For example, two asteroids can collide in the Belt. A fragment can drift into a Kirkwood Gap. Jupiter can pull the fragment from the Kirkwood Gap and throw it into an orbit near Mars. If the asteroid happens to have a close encounter with Mars during the next few million years or so, then Mars can throw the asteroid inward toward the earth. As a result, the supply of earth-crossers is constantly being renewed. Jupiter drags asteroids from the Kirkwood Gaps and hands them to Mars, and Mars hands them to the earth. Saturn can also pull an asteroid from a Kirkwood Gap and throw it directly at the earth.
“A lot of astronomers call asteroids the vermin of the skies,” Carolyn said.
Gene laughed, while his figure moved vaguely, outlined by a red reading lamp at the control desk.
“Gene and I,” Carolyn went on, “regard galaxies as the vermin of the skies.”
“There are far too damn many galaxies,” Gene said. “Carolyn has nearly reported galaxies to the Minor Planet Center.”
“They’re confusing,” she said. “The fainties can look like comets. I get so excited. Then I find out it’s only a galaxy.”
Gene’s father, George Shoemaker, bought a farm in the 1930s along the North Platte River in Wyoming, where he raised navy beans. Beans were a lucrative crop during the Depression, and George’s only problem was that his wife, Muriel, could not take farming beans. “My mother was gone like a shot,” Gene said. “I guess if she had been able to stand it, I would be a farmer right now.” Muriel Shoemaker left for Buffalo, New York, to teach school. Despite their differences over farming, George and Muriel stayed in love with each other and remained married. Gene would spend the winter in Buffalo and then take a train to Wyoming to spend the summer with Dad on the bean farm. Tiring of beans, his father went to Hollywood, where he eventually found work as a grip in a movie studio and where Muriel joined him again.
Gene
went to high school in Los Angeles, where he became interested in radioactive minerals. He majored in geology at Caltech during the years following World War II. “Caltech,” he said, “has always been a haven for space freaks.” The tendency, he said, began with the Hale Telescope. He liked to stand in the viewing gallery of the Caltech optical shop and watch Marcus Brown’s men, in white tennis shoes, work a polishing machine that traced Lissajous figures across the biggest piece of glass the world had ever seen. A few miles away, in Arroyo Seco, plumes of smoke occasionally erupted and a rumble shook the surrounding towns: Professor Theodore von Kármán and his students at the Jet Propulsion Laboratory were testing rocket motors. Then, during the summer of 1948, fresh out of Caltech, Gene found himself working for the United States Geological Survey, mapping uranium-bearing formations in the Paradox Valley of westernmost Colorado. The Geological Survey put him in a bunkhouse in a mining settlement. He would drive into the town of Naturita each day for breakfast, five miles on a dirt road through the Paradox Valley. One morning, when he was pounding along in a Jeep on the way to breakfast, a strange thought flooded over Gene. As he tells it, “I started thinking about von Kármán and those rocket motors. I also knew what was happening at the White Sands Proving Grounds. Wernher von Braun was down there, firing off a bunch of captured German V-2 rockets. All of a sudden I got this feeling in my bones. I said, By God, they are going to build a rocket—they are going to build a rocket and take men to the moon with it! What a thing! What an unbelievable thing! To be the first man on the moon! And what other person to explore the moon but a geologist? I decided right there that when they took applications, I was going to be standing at the head of the line.” He saw a flaw in his plan, which was, as he put it, “If you had told anybody in 1948 that you wanted to be a geologist walking around on the moon, they would have considered you a prime candidate for the lunatic asylum.” He swore an oath to do whatever he could to get himself to the moon but to keep his mouth shut about his ambition. At twenty years of age in Paradox Valley, something terrible happened to Gene Shoemaker. He became a geologist obsessed with the sky.