It had traveled through the silent void for countless millennia, since the formation of the solar system. A gray and black lump, it was well in advance and to the side of the rest of the hurtling swarm, a forerunner of what was to come. The irregular mass of iron and rock entered the outer atmosphere somewhere over eastern Iran, quickly heating up to become a flaming streak across the tranquil summer evening.
It had companions--specks and chunks that briefly lit up in long fiery trails before they burned out, or were deflected by the thickening blanket of air, spinning back out into space to begin a new path. But the big one flamed on, deeper and deeper, angling downward.
The air slowed it, but it was still traveling at a tremendous velocity when it struck the earth at Biskra, near the Tunisian border. In an instant the meteor obliterated the rambling Arabian town. Where forty-six thousand people had lived moments before there was only smoke, a steaming crater whose bottom was a bubbling pool of sand and rock turned into lava, and death. In the suburbs, along the roads and trails, lay blackened bodies, children and animals and twisted burned things. Every building was leveled. Sand dunes were fused to molten glass or blown away to the bedrock. Brick, flesh, machines, dolls, the mosque, animals, everything: molten, vaporized, burned.
The immense ball of orange flame that was the death knell of Biskra was seen by a crop analyzer on Space Station Three. She stared, blinked, then reached for the emergency microphone. Earth had been struck by the largest meteor in modern times.
* * *
Zakir Shastri was normally calm, even placid, as befitted an astronomer, whose chief was patience. But now he bit nervously on his full lower lip, his dark eyes intent upon the words and numbers building in glowing lines upon the screen before him. He took a deep breath and exhaled it in a sigh. He glanced away from the phosphor dots, out the side port. Earth swung into view. Across the nightside, dotted with smudges of light, something suddenly scratched a long streak of orange light. Then it vanished. Soon, another. Then two dimmer ones. He sighed, closed his eyes to blank out the sight, and chewed nervously on his lip.
The Indian astronomer sat strapped into a chair bolted to the platform. He was at the sighting focus of the main telescope, where he could "eyeball" the precise fix he wanted. This was the place where he felt most at peace in the entire Orbital Astronomical Observatory. It was not vastly different from the famous cage at Palomar, where generations of astronomers had labored through the years in the biting cold of the California mountains. Now, pollution of the seeing conditions by the billion lights of the megalopolis below made Palomar a risky site for some kinds of observations, particularly for taking spectra of dim objects. And, of course, Palomar was the prime example of the basic limitation of all Earth-based telescopes: precision of resolution. Visitors to Palomar and other great observatories always thought the point of building such a giant telescope was to see more detail. In fact, Palomar couldn't "see" any better than a twenty-centimeter backyard telescope. The rippling air above any telescope scrambled light waves coming in, erasing any detail smaller than about a half-second of arc. Telescopes bigger than twenty centimeters were just buckets for catching more light; they couldn't make out any more detail than their smaller brethren. Only by putting telescopes in orbit could astronomers see any better. So the eighty-centimeter tube directly in front of Shastri represented a new dimension in peering at the universe. Without the obscuring blanket of air, this telescope could see fine features in the optical, ultraviolet, and infrared ranges. It would, in time, open a universe in a way the great Hubble could never have dreamed.
The lean astronomer bent over the eyepiece. Despite all the machinery and computers, sighting on a distant fleck of light was best done by the human eye and hand. He peered intently through the prime eyepiece, his long dark fingers on the knobs.
There: a muzzy patch of light. Dust and gas and pebbles. It was noticeably dimmer than the last time he looked. Soon the image would fade into the background. At the center of the pale white cloud was a pinpoint of light. The source of all the debris around it. An ancient rock, chipped over the aeons by small collisions. Shastri watched it drift sideways in the focus, declination increasing.
He estimated the are width and did the numbers in his head. His face contorted in a brief, bitter grimace.
Then he caught the dim dot, calibrated it, and set the exposure time electronically. A deep plate this time, to resolve as much structure as possible in the cloud. He thumbed the proper button and sat back. He had only to wait.
Later he could measure the plate, for precision. But for the moment the computer programs would reduce the data from them, on on-line tracking. He switched on the display again and watched the figures building on the screen in long luminous lines. He wiped his palms on the thighs of his gray jumper. Once again he checked the computations, laboring through each step to be certain, the greenish screen light and the dim red bulbs making his face strange.
Shastri sat back, his face grave. Much of the life had gone out of his expression.
After a little while, he unshielded the side port and gazed out. The telescope's spherical housing was attached to one end of the three-hundred-meter-long Orbital Astronomical Observatory, commonly called Station Three. The sphere containing the telescope counterrotated against the gravity spin of the station itself. Around Shastri was the tubular bulk of the main optical telescope, dimly lit in red, and on the platform was the computer support system that controlled it.
Shastri shifted beneath the white strap that held him to the aluminum chair, glanced again at the figures building on the screen in long luminous lines, and wiped his palms on the thighs of his gray jumper. Impatiently Shastri turned and studied the readout screen from Station Six.
A third away around the same Earth orbit was Six, with its immense five-kilometer radio telescope. Radio astronomy, he thought, was where all the action was these days. But he knew if he really needed it, one call would enlist that giant ear/eye.
Both Stations were in Band Five, the outer Terran orbit. Both were awkward, bulbous objects, with spheres on protruding columns, radio discs, telemetry masts and landing docks sticking out at what seemed like random angles. Station Three had accreted over the years, growing, adding, but rarely subtracting. Shastri recalled his surprise at finding, deep within the complex, the Apollo tank which had been the foundation rock upon which the entire complex had been constructed. It was now used only for luggage storage.
Shastri shifted his hooded eyes at the dull boom of an airlock opening. He heard the clatter of someone moving awkwardly into the weightless environment of the observatory sphere. In a few moments Fakhruddin Radhakrishnan, Shastri's lean and bearded young assistant, came wriggling through the tube passage. His eyes were wide and concerned, dark with dread. His white turban was hastily wrapped, its loose and floating in the air. He scrambled into the platform and secured the wandering cloth absently as he asked, "Is…is it true?"
Shastri indicated the large screen which was still printing out figures. "Starsearch is comparing the photographs now, and eliminating all the known and logged asteroids." Radhakrishnan pulled himself hand over hand to the console, twisted into a seat, and fastened the restraining strap. Then he peered anxiously at the screen.
"You backtracked on the trajectory?"
Shastri nodded. "Luckily it showed on a plate here, and at the Planetary Studies' scope at Six. It's an Apollo object. What it's doing in this area is…" He stopped talking when the printing creased coming on the screen. He leaned forward, muttering as he read the information.
"Ah, elliptical orbit…the long axis--the semimajor axis--of um, only zero point eighty-eight…um…nearest approach to the sun is zero point three astronomical units." Shastri sat back with a grunt, his eyes staring moodily at the screen.
Radhakrishnan pointed with a thin brown finger. "The orbit is tilted to the ecliptic plane." He looked at Shastri. "Most of the Apollo asteroids stay efficiently away from the orbits of the inner planes, don't they?"
Shastri nodded, his face shadowed. "Yes. Any other orbit and…well, most of them would have hit Mars and Venus--or Earth--long ago. And probably did."
Radhakrishnan frowned, staring at the screen. "The Apollo asteroids we know cross the ecliptic plane only at some intermediate point between the Earth and the sun, don't they?"
Shastri nodded, his lips drawn down. "Then…" Radhakrishnan swallowed hard, his eyes blinking as they stared at Shastri. "Then the swarm has been flattering its orbit, bit by bit…drawing closer to Earth as it…as it turns on its outer orbit, before…before returning toward the sun?"
Shastri did not answer. His fingers shifted the information on the screen into storage and then pecked out another set of instructions. The screen lit up with a computer simulation of the sun, the orbit of Earth, the moon, and the known Apollo objects. Then he added the orbits of the eccentric asteroids: Hildalgo, Adonis, Amor, Eros, Ceres, and Apollo. Then Hermes, Pallas, Juno, and Vesta.
"Just to be safe," Shastri murmured, adding tiny Hygeia, Eunomia, Psyche, Davida, Hebe, and Iris. Then other, still smaller "tagged" asteroids were put into the mix. The screen was a mass of elliptical ovals. Shastri hesitated, sighed. Then he took what was known of the orbit of the asteroid that had extinguished the Tunisian town and put it into the system. The glowing line, red against the white of the earlier computations, built up into the orbit of the meteor that had struck Earth. Quite plainly they saw the orbit flattening, tilting down into t...
