Darvin sat down himself, the heels of his hands against his temples, and began to work his way through the notebook, trying to see where his colleague had gone astray. Every so often he turned to the calculating machine. Within an hour he was doing this so often that it clattered and rang like the till in a busy shop. Then it fell silent, and Darvin gazed in gloomy triumph at the notes.
He didn’t hear Orro arrive. A short noonday shadow fell across the page, and he looked up.
“I’ve found your problem,” Darvin said.
“You have?” said Orro. “Then I forgive the intrusion.”
Darvin jumped up and clapped Orro’s shoulder. Orro winced and put a hand to his head.
“Sorry,” said Darvin, pacing across the floor, and turning to pace back. “It’s very simple. You’ve assumed that the comet is outside the orbit of the Warrior.”
Orro shook his head, then clutched it again. “I haven’t assumed it. It is outside. Not far, but definitely outside.”
“It can’t be,” said Darvin. “That’s still too far away from the Sun for a comet to be visible, let alone as bright as it is.”
“Does the anomaly disappear when you recalculate on the other assumption?”
“I haven’t got that far,” Darvin admitted.
“I thought not,” said Orro. “In any case, you needn’t bother. That was where I started.” He reached for a shelf above the table, and pulled down another notebook. “Check that one too if you want. I found the anomaly, and then I realised it couldn’t be right, because the comet’s path is not perturbed by the gravitation of the Warrior, or of the Queen. My calculations on the assumption that it was much farther out — the ones you’ve been looking at — are my second attempt. And the anomaly of apparent deceleration is still there. Not only that, but you’ve just pointed out another one, the comet’s visibility and brightness. I tell you, it’s enough to drive a physicist to drink.”
Darvin laughed. “I underestimated you,” he said. “I thought you were missing something that would be obvious to an astronomer. You weren’t. This is good solid reckoning, Orro.”
“Very well,” said Orro. He looked relieved. He sat on the perch and caught the table edge with his toe-claws and leaned back. “Let’s spit the rind and chew the pith.” He closed his eyes for a moment, with a faint shudder. “Metaphorically. We have an anomalously bright celestial object, anomalously distant, anomalously decelerating. It is traversing the region of the Queen of Heaven’s Daughters, the green stars. What hypothesis springs to mind?”
“None,” said Darvin. “No celestial object decelerates on its way in towards the Sun.”
“No natural celestial object. Very well then. It must be an unnatural object, or rather, an artificial one.”
Darvin laughed. “An alien spaceship?”
Orro shrugged. “Call it that if you must. It may be something not conceived of even in engineering tales.” He pointed over his shoulder at the calculating machine. “I’ve sometimes speculated on what could be achieved by such a machine, given a few eights-of-eights of years of progress in the art… but leave that aside.”
“Yes, I should think aliens are quite enough to be going on with, leaving aside mechanical thinkers.” Darvin punched his friend’s shoulder. “Come on! This is quite unscientific! It’s always better to seek the simpler explanation.”
“You have one?”
“The glimmerings of one,” said Darvin. “Just as speculative as yours, I admit, but requiring fewer… supplementary hypotheses.”
“Give us it then.”
Darvin paced back and forth a few times before replying. In truth he was not as sceptical of aliens as he had sounded. The possibility was an old and respectable one in the astronomy of Seloh and Gevork; even in religion, the green tinge of the Queen had been associated with life, and the spectroscopy confirmed that. There had even been a delightful legend that the Queen of Heaven’s Daughters had been given life by the Queen, and while astronomers discounted that, they allowed that the green tinge of the Daughter stars might indicate the presence of life on any planets around them, while admitting they had no idea how such hypothetical life-bearing planets could filter the light from their suns. There was one outlandish, but established, suggestion that some kind of green plant could grow in space itself, perhaps from the surfaces of comets, but the difficulties of this idea were as obvious as the absence of imaginable alternatives to it.
“Suppose what we have here,” he said, “is a natural object, but one unknown to astronomy. A new kind of comet. We know that a comet’s tail consists of gas glowing in the Sun’s rays.”
“Yes,” said Orro.
“Now, the gas is given off as the comet warms up, on approaching the Sun. Now if, if there were a kind of comet or similar body that began to outgas much farther out from the sun, the flow of gases would — if aligned towards the Sun — slow down the comet and make it brighter than it would otherwise appear.”
Orro closed his eyes and tilted his head back. His lips moved. “That might just work,” he said at last. “It would require some damned ticklish and unlikely coincidences: mass, orientation, specific impulse… am I right in thinking that cometary outgassings don’t normally have any effect on their orbit?”
“You are,” said Darvin. “This would have to be, as you say, something quite different from outgassings as we understand them. The gases propelled outward by radioactive heating within, perhaps?”
“Radioactivity is a remarkably faint source of power,” said Orro. “Certainly in any concentrations found in nature, though there have been some experiments and calculations… all very speculative stuff, of course.”
Darvin had never heard of work along these lines. “In Gevork?”
Orro opened his eyes and stared at him; it seemed, through him. “Speculation.” It wasn’t clear to just what Orro applied the epithet. He waved a hand. “Ignore that. We can only describe what we incontestably have evidence for. So let us describe it.”
“How?”
Orro jumped off the perch, strode forward, and clasped Darvin’s hand. “A joint note to the journals? Or failing that, the physics wire? Does not ‘A Distant, Decelerating Celestial Object: Some Observations,’ by Darvin and Orro, of Five Ravines, have a certain ring to it?”
“It does,” said Darvin. He returned the handshake. “If only I didn’t suspect that we’ve both made some ghastly mistake, which some undergraduate will spot straight away, in which case it’s a title that’ll ring in our ears for the rest of our lives.”
They finished checking the calculations that evening. By midnight they had written the paper. It was brief, detailed, mostly mathematical, and included no speculation whatever about the nature of the decelerating object.
“You know,” Darvin said, glancing it over one last time, “I can’t help thinking this looks a bit trashy and sensational.”
Orro didn’t laugh. “When I close my eyes, I see its title as a screaming headline in large black type.”
“That’s fatigue,” said Darvin. He helped himself to some tea. “But yes, I do worry about the effect on public opinion. In engineering tales, the arrival of aliens is invariably followed by mass panic.”
“That’s fanciful,” said Orro. “It has never been tested.”
“Well, in the nature of things, no,” said Darvin. “However, there was one incident back in the Dawn Age, when the first observations of signs of life on the Queen were published. That led to, if I recall my history books, a stock market bubble, a subsequent collapse, and a brief frenzy of religious persecution.”
“That was the Dawn Age,” said Orro. “We are now in the Day.”
“So we like to believe. A day in which dirigibles almost too high to see patrol our skies above the Broad Channel. When the Broad Channel itself is patrolled by warships from both shores. A day in which war with Gevork is openly spoken of, and not just in engineering tales.”
“And a day in which many such as you and I cooperate like civilised men.”