She saw moving objects dotted all over her films; there is an almost unbelievable quantity of natural material floating around the solar system. Most of what she saw were Main Belt asteroids, many of them, no doubt, unknown objects. Comets were fuzz balls—a fog of gases flowed off them. Comets gave her a thrill. There was something about that misty haze that made her heart leap in her throat whenever she thought she might be looking at an undiscovered comet.
She kept her eyes moving, eight hours a day. “I try to move the film steadily across my field of view, without stopping,” she said. “If you start paying too much attention to things, you start questioning everything: Is this an asteroid? Finding asteroids gets to be instinctive.” When she saw what looked like a Trojan planet—a dot floating just in front of the stars—she marked it with a red pen. “These Trojans are fainties, kind of crummy-looking,” she said. They resembled dust particles stuck to the surface of the film. She got into a habit of running her finger lightly over anything that looked like a Trojan planet, and sometimes a “Trojan planet” went away. She did not want to report the changing locations of a piece of dust to the Minor Planet Center. The stars formed trapezoids, rings, letters—her private alphabets. She would become intrigued with a galaxy. She would imagine herself as a traveler in space, approaching that galaxy. She explored globular star clusters. A globular cluster is a spherical cloud of several hundred thousand stars that orbits independently through the Milky Way. The sight of a globular cluster could cause a sharp detour through the Trojan cloud. At times she would forget what she was doing. She would come to her senses, realizing that she had become lost in a film and had no idea where in the film she was traveling. At other times she would wake up suddenly at home in bed—because if she spent enough time with the microscope, she began to find asteroids in her sleep.
After she had scanned and marked a set of films for likely Trojan asteroids, she made rough measurements of their positions, and then looked them up in a book that astronomers call the Russian Ephemeris. (The Russians keep track of asteroids for everyone else.) “I picked off most of the known Trojans that way,” she said. She found plenty of Trojan planets, and they already had names.
The job consumed weeks of tedious effort. “I wouldn’t work this hard if it wasn’t so much fun,” she said. In late November 1986, she found a speck that was not listed in any catalog, and it did not go away when she ran her finger over it. That same day she found another speck. She measured their coordinates using a machine called a measuring engine, and typed her measurements into a computer linked to the Minor Planet Center.
The next morning she received on her computer a message from Brian Marsden: CAROLYN: EXCELLENT! He informed her that she had sighted two unknown Trojan planets. He gave them the temporary designations 1985 TE3 and 1985 TF3. These planets had never been seen before. They were huge minor planets, each about fifty miles across—“elephants,” as Gene called them. They were bigger than many of the moons of Jupiter, and, as Carolyn put it, “They are ours.” Like all Trojan planets, they were at least as black as charcoal and probably blacker.
A week later she found another unknown Trojan, 1985 TG3. Then another, 1985 TL3. She also picked up a Trojan that a team of astronomers in Denmark had recently sighted, and she helped the Danish astronomers get a better fix on its orbit. She also recovered a Trojan—a Trojan that had been sighted by the Dutch astronomer E. J. van Houten in his original survey of the Trojan clouds but had been lost. In the end, she found four new Trojan planets and helped to secure identifications of two others. She said, “It’s been an education for the eyeball.”
Gene was pleased. He said, “The implication is that there is just a huge number of Trojans out there. We are only finding the elephants.”
In order to give these planets names from The Iliad, the Shoemakers would probably have to wait for a year or longer, because an asteroid must be seen on three orbits around the sun before it becomes eligible for naming. Gene hoped that they would not have to scrape the barrel of The Iliad, but he was afraid that by now there might not be any heroes left.
The solar system remained a mysterious object to Gene Shoemaker. He had been wondering for a long time where these Trojan planets had come from. He had been wondering how they fit into the origin of the bunch of dust in which we lived. The common wisdom, he said, held that the Trojan planets were leftover pieces of the same material that had clumped together to form Jupiter, during the accretion of the planets. He had not often made a habit of buying common wisdom. “Lately,” he said offhandedly, “I’ve been working to cobble together a theory. It would account for the formation of the planets Uranus and Neptune, the creation of the Oort comet cloud, the existence of these funny black objects near Jupiter, the late heavy bombardment of the moon, and the formation of the earth’s oceans. If I ever get a week free, I’ll write that one up.”
He thought that he could explain the existence of water on earth and the existence of the Trojan planets all in one story. It was a hypothesis, a hunch about what had happened back then, when the solar system was coming together. He thought that the formation of the earth’s seas might have been a part of an accretion process. Uranus and Neptune were large, icy planets, made of methane and water, with a rocky core. They had formed near the outer edge of the accretion disk that had become the solar system. During the era of fast planetary growth, the planetesimals—balls of silica, iron, tar, and ices orbiting the sun—had pounded together and welded to form planets. The accretion of the outer planets had not been a gentle process. As Uranus and Neptune grew, they experienced near misses with their own planetesimals. They played crack-the-whip with pieces of themselves; they whiplashed their planetesimals all over the place. Most of this debris was ejected into orbits beyond Pluto, where it is now called the Oort comet cloud. Gene felt that the Oort cloud was probably a haze of ice ejected from the solar system during the creation of the outer planets. Some of these wild pieces of Uranus and Neptune, rather than looping out to the Oort cloud, fell inward, past Jupiter. As they neared the sun (which had caught fire by then), they became dramatic comets.
Gene suspected that Jupiter had acted as a flytrap, perturbing these comets as they floated by, trapping them in the Trojan areas. Some force had to have decelerated these comets in order to trap them near Jupiter. Orbital specialists had not been able to come up with a mechanism that would slow down a large comet, but Gene had an idea: perhaps these comets had collided with small pieces of debris sitting in the Trojan areas. The comets had bumped into bits of rubble floating in the Trojan areas, stalled there, eventually burned out, and lost their tails.
He said, “My hunch—and this is Shoemaker’s private view of the world—is that the Trojan planets are all extinct, captured comets.” There might be nearly a quarter of a million black planets out there in the Trojan clouds, but according to Gene they represented “just a sniff of the total mass that was flowing through that region during the formation of the solar system.” The planet Jupiter had thrown some of that mass into earth-crossing orbits.
With the naked eye one can see that something violent had once happened to the moon—the creation of the dark plains known as the lunar seas. To the naked eye they look like bruises. Galileo had thought they were oceans, but they are scars left over from what Gene calls the late heavy bombardment of the moon—immense impact structures bearing names such as the Ocean of Storms, the Lake of Death, the Lake of Dreams, Tranquillity Sea, and the Sea of Serenity, where Gene might have walked if he had only been eligible to be an astronaut. He believed that the lunar plains might have been made by stray chunks of Uranus and Neptune hitting the moon. With all that material floating around, there would have been a late heavy bombardment of the earth too.
“How do you go about fund-raising for the earth’s oceans?” he had wondered. The standard theory for the origin of water on earth said that the water had come from volcanoes that had plumed water vapor into the atmosphere. “Essentially the standard theory
said that water sweated out of the earth,” he said. “We call that juvenile water.” He thought that the best place to look for juvenile water was the sky. “You can envision one of these big comets smacking into the earth at twenty kilometers per second,” he said. “The projectile would vaporize as it hit a rocky surface. A lot of the contents of the comet might rain out—you might get rains of water, carbon dioxide, and ammonia. The water would collect in the lowest basins. It would take about two hundred of the largest Trojan planets to make the ocean—biggies about two hundred kilometers across, Trojans the size of Hektor or Agamemnon. But there are bigger things than Hektor out there. Pluto, for example. Sure! The planet Pluto might well be a huge, extinct comet! If you could shake Pluto loose out of its orbit and bring it nearer the sun, you would have a comet, because the ice on it would start to steam away, forming a tremendous tail. One or two real big comets the size of Pluto, and maybe fifty Trojan-sized comets, and a bunch of itty-bitty stuff—that would deliver you the ocean. There’s a problem with this theory. When I calculate the expected cratering rate of the earth during the late heavy bombardment, I get too damned much water!”
Comets probably contain hydrocarbons, and they may also contain traces of amino acids, the building blocks of protein. Gene did not think that amino acids could survive the heat of a large impact. But a small impact was another matter. He said, “Small cometary debris—there was plenty of it around during the late heavy bombardment—could be decelerated in the upper atmosphere and reach the surface of the earth intact.” The earth’s primeval seas might have contained a broth of water-soluble organic compounds, derived from steaming hunks of comets. The human body is 70 percent water, and much of the rest of it consists of organic, carbon-based molecules. To Gene Shoemaker it seemed not impossible that the human body might be largely former comet.
The Trojan planets, in the Shoemaker view of the universe, were extinct cometoids covered with a goo of carbonaceous dust or tar. What you might have out there, Gene thought, was an asteroid belt made up of nearly a quarter of a million ancient comets. “The existence of large Trojan clouds,” he said, “would amount to circumstantial evidence for a huge flux of comets early in the history of the solar system. I think that these Trojan planets are preserved samples of the same guys that were delivering the oceans to the earth. The point of this is that there’s a whole other asteroid belt out there near Jupiter still to be explored.”
Don Schneider’s office at the Institute for Advanced Study, in Princeton, New Jersey, looked over meadows to deep woods, which were beginning to incandesce from autumn frost. Don was sitting at a table that held two computer screens, two keyboards, and a video monitor. A photograph of the Heartwell farm hung on the wall. The time had come for an attempt to mine the sky for quasars. His lifework, or so he claimed, consisted of about two hundred reels of computer tape and a program named Cassandra. The tapes contained electronically recorded images of some of the things out there—of cataclysmic stars, of quasars, of packs of feeding cannibal galaxies, of gravitational lenses, and of the tapestries of sky generated by Maarten Schmidt’s search for the redshift cutoff. Cassandra was an image-processing computer program. She could recognize patterns.
“Cassandra,” he said, “has been searching a crowd of faces. She has been looking for interesting faces.” He hit a key, and an image of sky came up on the screen, showing galaxies and stars with candle flames emerging from them—smears of spectral light. The screen displayed a moment from a night’s transit—a piece of sky that happened to be located within the Trojan cloud of planets. The screen was painted with many spectra—the broken light of about a hundred stars and galaxies, and possibly a Trojan asteroid or two. (Cassandra had no way of recognizing Trojan planets.) Don turned to a pile of papers and studied a jagged line plotted on paper—a line describing the peaks and valleys of color in one particular object on the screen. He studied the paper. He peered at a candle flame on the screen. “Ooo,” he said, “that looks promising.”
Cassandra had identified this thing as a possible quasar.
He put his face closer to the screen and studied the object. “Nope, that’s an M star,” he said. “A red star. Cassandra thinks its a quasar.” He marked an X on his paper. He hit a key, and a new image of sky came up.
Out of a tapestry of sky containing about 120,000 stars and galaxies, Cassandra had picked out a list of about 2,000 quasar candidates—objects showing bands of bright color resembling the light of quasars. Cassandra tended to discover things that were not quasars: stars saturated with metals, galaxies with glowing cores, and glitches in the data. Don had to check Cassandra’s discoveries by eye, to weed out the false alarms. Then he and Schmidt and Gunn planned to return to the Hale Telescope to take detailed spectra of the remaining candidates. They hoped that a handful of these candidates would turn out to be quasars. Given luck, one or two of those quasars might turn out to be extremely distant, deeply redshifted monsters.
He had been keeping two VAX computers running simultaneously around the clock for weeks, eating galaxies by the megabyte. He said, “I’m just a bit player here. No pun intended.” He did not want a single quasar to slip through his nets. Maarten Schmidt wanted nothing less than a perfect quasar filter. “Maarten Schmidt casts a long, thin shadow,” he said. If Cassandra missed any quasars, then the search for the edge of the universe would end in New Jersey—“And I’ll be heading south of the border,” he remarked.
He offered to introduce me to Cassandra. She could talk a little. He sat down at another of his computer terminals and hit a few keys.
Cassandra said, on the screen, MAY I HAVE YOUR LAST NAME, SIR?
“Schneider.”
HELLO, MASTER!! I HOPE I PERFORM SATISFACTORILY.
Don said, “She calls me Master. Other people she calls Junior. Give her your name.”
I typed, PRESTON.
GREETINGS! I’VE BEEN WARNED ABOUT THE PRESTONS.
He said that Cassandra had previously been notified of my arrival. “But if the program doesn’t know your name, it dies. It says, ‘That is no way to address a lady.’ ”
Cassandra could do all kinds of things. She could do an “auto object grunge,” in which she measured the location of every star within a crowd of stars. She could transform herself into a hunter / seeker, looking for the exact center of a galaxy. She could plot the colors of light from a quasar into a jagged line, like a stock-market chart. She could also construct artificial stars and galaxies, for testing purposes.
Don said, “Let’s play God,” and typed a few commands to Cassandra.
She said, FORMING SKY.
A night sky appeared on a nearby screen, speckled with stars. An imaginary sky created by the computer.
She said, I AM BUILDING A STAR.
A bright star appeared on the screen.
I AM BUILDING A GALAXY.
Nothing happened.
“What’s going on?” Don muttered.
A galaxy appeared.
“Ah! There we are,” he said. Typing fast, he told Cassandra to make a globular cluster of stars.
FORMING SKY.
Nothing happened.
We waited.
Nothing continued to happen.
“Uh-oh,” he said. “It’s making a hundred thousand stars. That will take days.” He told her to try something less ambitious.
After a while a shotgun blast appeared on the screen—a globular cluster—and she said, I HAVE CREATED 200 OBJECTS.
Cassandra contained something like fifty thousand lines of code. “I don’t know the exact number,” he said, “because it’s always changing.” He had chosen the name Cassandra for a reason. Cassandra, he explained, had been the daughter of the king of Troy. The god Apollo had fallen in love with her and had given her the gift of prophecy. But when Cassandra had refused Apollo’s advances, he had cursed her and told her that her prophecies would come true but that nobody would believe them. During the Trojan War, when the Greeks had left a wooden
horse by the gates of Troy, Cassandra had warned her fellow Trojans of the danger. They had ignored Cassandra. “My program works,” he said, “but nobody believes it.”
A large program such as Cassandra can often be passed around during its development. The program had been started by one Robert Deverill, who had given it to Don Schneider and to a Caltech classmate of Don’s named Peter J. Young. P. J., they called him. Don and P. J. had both entered Caltech in 1976 as graduate students in astronomy. They were the astronomy class that year—a class of two. P. J. Young was a thin Englishman with a rapid way of talking and a quick sense of humor. He was considered to be the most brilliant astronomer that Caltech had produced in many years. Don and P. J. collaborated in developing the Cassandra program. But Peter J. Young was a victim of deep depressions, which he covered up—no one knew about them. One day not long after he graduated, P. J. Young shut the door of his office at Caltech and killed himself. He had been one of Don’s best friends. The loss left Don with an orphan, the computer program, whom Don had continued to raise and educate. Now he was the only person on earth who understood Cassandra.
Cassandra would soon be hunting / seeking through pictures taken by the Hubble Space Telescope. She had come a long way, but P. J.’s death had left Cassandra with a dilacerated heart. The pain would never go away, but Cassandra hid it fairly well now, although every time her master closed the program, she asked him, DO YOU REALLY WISH TO LEAVE ME? and if he answered yes, then she Said, LIVE LONG AND PROSPER, MASTER.