board. The new shift had arrived, and they were tiptoeing around, trying not to look curious. Ten minutes later, lights started blinking all over the board as the Mars computer fed data via radio into the Farside computer’s memory buffer register. The computer, consulting its hydrogen maser clock, corrected for transmission delay.
Before astronomers had set up shop on Mars, they had had to wait six months to measure parallax. You took a picture of your target star, and when the Earth had traveled halfway around the sun you took another picture on the same plate and measured the apparent shift. Now you could triangulate by taking sightings from the Moon and Mars simultaneously.
Ruiz watched the figures unreeling on the LED displays, his coffee forgotten. In his mind he translated them into a triangle with a base line that was 234 million miles wide. If the X-ray source was anywhere within a hundred light-years, he’d get reliable results.
Two glowing dots appeared on the viewplate against a background of stars; the computer had enough data now to attempt a preliminary visualization. Who had asked it to do that? He looked up—that technician, Maybury. She was efficient. That fool with the shaved chest was doing nothing except stand around looking important.
Ruiz looked back at the screen and blinked. The dots had stopped jiggling. They were impossibly far apart. The parallactic shift was … huge!
The damned thing was less than a light-year away!
He snatched the lightpad from a startled Mizz Maybury and made his own rough calculation. His answer approximated the computer’s average figure: a distance of about half a light-year. The Cygnus source was
Something soft nudged his arm: Mizz Maybury’s breast. She was leaning across him, thrusting a piece of paper in front of him, trying to get his attention.
“Dr. Ruiz!” she said urgently. “I thought you might want—that is—I asked the computer to pull out the most recent planetary data. The positions of the outer planets—I mean, there’s a discrepancy of several seconds in the longitude and declination of both Neptune and Pluto. It might turn out to be simple observational error, but—”
He waved her aside. “In a moment, Mizz Maybury.” He was staring intently at the screen that showed the values for the base angles. The computer was constantly updating them as it refined and reaveraged its data. They held steady up to the eighth decimal point, then jumped back and forth a good deal, but the trend of the figures was definitely higher.
The thing had to be moving
He heard a gasp behind him. Maybury was looking over his shoulder.
“That’s right,” he said. “It appears to be moving toward us at something more than ninety-eight percent of the speed of light.”
Over at the data screen the junior resident cleared his throat. He was perspiring, and the green ident disk on his chest was coming unstuck. “That means it’ll be in the vicinity of the solar system in about six months,” he said.
“At its present speed, yes,” Ruiz said.
He drummed his fingers on the arm of the chair. Finally he said, “I don’t suppose we’ll really have enough data till we’ve observed it for a few more days, but why don’t you have the computer generate a projection of the path of the Cygnus source through the solar system.”
Maybury and the young man got busy over at one of the consoles. Ruiz could hear them whispering together, having some kind of dispute, but he wasn’t paying attention. He was thinking about the trip to Earth he’d probably be making some time in the next twelve hours, dreading it. He glanced up and saw the junior resident, an angry flush on his face and chest, step away from the console and stare sulkily out the observation window. Maybury was hunched over, shoulders tense, her fingers flying over the lightboard, her bare toes twiddling in unconscious rhythm. At last she straightened up and turned in her chair.
A flat disk grew in the square darkness of the holo well. It looked something like a target, with the sun and the orbits of the inner planet crowded together to make a bull’s-eye. In the computer’s stylized representation, Pluto’s orbit was a tilted hoop intersecting the orbit of Neptune, which had briefly replaced it as the outermost planet beginning in 1987.
A yellow dotted line with an arrowhead represented the probable course of the Cygnus source. It wiggled back and forth a bit as the computer changed its mind, but it always intersected the plane of the ecliptic somewhere near the edge of the bull’s-eye.
Ruiz canted the image for better perspective and zoomed in so that Jupiter’s orbit was outermost. Now he could see the positions of the inner planets—colored beads strung on those glowing tracks, and necessarily out of scale. Six months hence, Mars would just have overtaken Jupiter, and Earth would be rounding the Sun to catch up.
That X-ray holocaust from Cygnus was going to penetrate the plane of the solar system somewhere between the orbits of Jupiter and Mars. It would pass within 4 A.U.s of Earth.
Ruiz rose out of his chair very carefully, like an old man, and walked over to the observation window. He took another long look at Cygnus, knowing it was futile. If the 500-inch telescope couldn’t see anything, he certainly wasn’t going to see anything with the naked eye. The duty tech made no attempt to follow him with her piece of paper. Even the junior resident had sense enough not to say anything.
Dr. Mackie arrived a few minutes later, still wearing his pressure suit, his helmet tucked under his arm and his turkey neck sticking out of the collar ring. He saw the look on Ruiz’s face. “What’s wrong?” he said.
Ruiz was a tough old bird. He had grown up in the squalor of a refugee camp on Long Island in the years after most of Manhattan had been rendered uninhabitable by the bomb, made of stolen reactor wastes, set off by the New England Separatists in 1998. He had clawed his way to the top on his own merits, despite the twin handicaps of poverty and a provisional ident. There wasn’t much that could unnerve him.
But now his face was gray as he turned to Mackie.
“I’m putting you in charge, Horace,” he said. “I’m going down to Earth to tell them that the human race has just been sentenced to death.”
Chapter 2
Tod Jameson flung up a gauntleted hand to protect his faceplate and yelled: “
He grabbed a startled Li Chen-yung by an air hose and spun him around. There was just enough time to plant both boots against Li’s quilted blue spacesuit and give him a mighty shove; then the flat, perforated pad of the landing leg went sailing past his head like a gigantic flyswatter. Its stately slow motion was deceptive. There was enough mass behind the pad to grind him into the hull like a bug. His spine crawling, Jameson saw it crunch its way through several honeycomb layers of the Callisto lander’s skin and embed itself there, trailing springs and broken struts.
He was drifting outward in a direction opposite to the shove he’d given Li. Earth filled the sky, a colossal backdrop of sparkling blue-and-white whorls. Against it was silhouetted the unfinished framework of the Jupiter ship, just a couple of miles off, a spidery wheel with a spear through the hub.
Li’s voice crackled in his helmet. “Thanks, buddy,” he said.
“
He located Li, a starfish shape floating in emptiness, pinwheeling crazily. As he watched, Li brought the spin under control and fired a short, economical burst from his suit jets that sent him back toward the squat bulk of the landing vehicle.
