Salo prompted, “And we are after Gershon because—”
“Planetary protection. He’s been threatening to do more than take a photograph at his target. Mining, maybe. We were appointed Prefects pro-tem, with the authority to go after him, and grab him, and clean up as necessary.”
Salo nodded. “If he does go beyond the Last Small Step parameters.”
“Stavros Gershon,” I said, my frozen brain slowly thawing, “believes he is descended from one of the first on Mars, so carrying on the family tradition. And his target—no name, I can never remember the catalogue number—”
“Actually, it has a name now. Gershon gave it one—or, he says, he rediscovered it.”
Which bit of oddness reminded me of what I’d been hearing when I woke up. “Why were you reading Gulliver’s Travels?”
He looked impressed. “Well recognised. Part III, chapter III. But it wasn’t me reading. It was a transmission from Gershon, on the Last Small Step. From beginning, unpause.”
On a wall screen, a smiling face appeared, framed by a standard lightweight pressure suit hood. A ship’s cabin. “Hello. I am Stavros Gershon...”
I sipped my soup, and wondered why I didn’t need to pee, and stared.
Stavros Gershon looked maybe fifty years old. He didn’t much resemble his famous ancestor, but then after the huge mixing of mankind during the decades of the Chaos, few of us looked much like our great-grandparents, probably. I had to admit his ship, the clunkily named Last Small Step, looked spacious, even comfortable, compared to our bare-bones Malenfant. Gershon must have been donated a lot of stipends by a lot of supporters.
“And I suppose, as I approach the minor planet Voga, that you are wondering why I am reading to you from a text first published in 1726, over five hundred and forty years ago...”
“Pause,” I said. “Voga?”
“I checked out the name,” Salo said. “Bounced it back to the Archives on Earth. It’s pretty obscure—a legend that may have its origin in fiction, even...”
“What legend?”
“Of a planet made of gold.”
I stared at him, and at Gershon. “Gold? That’s... insane.”
“Probably. But there’s a logic to it. I think.”
I was thinking too, but very slowly. “And it has something to do with Gulliver’s Travels?”
“You got it. Unpause.”
Gershon rattled through the passage I’d heard earlier, and read us some more: “They (that is, the astronomers of the flying island of Laputa) have likewise discovered two lesser stars, or satellites, which revolve about Mars; whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost, five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars; which evidently shows them to be governed by the same law of gravitation that influences the other heavenly bodies. They have observed ninety-three different comets, and settled their periods with great exactness...”
“And so on.” Gershon grinned into his monitor. “You see? It’s all in there. The clues to the treasure. Sitting in plain sight for five hundred years.”
“And you’re the genius who figured it out,” Salo muttered. “What treasure, though?”
I studied Gershon’s face. I’m more interested in people than Joe—an age difference thing, maybe. Gershon was grinning, but there was a kind of desperation there, I thought. As if he didn’t fully believe his own logic, as if there was something deeper driving him. Which is probably true of all of us. What are you doing out there, Gershon? What treasure? And what do you really want?
Meanwhile, memories were reassembling in my reluctantly waking brain like the pieces of a puzzle. Thud. Thud. “And this was why we were sent after him, in such a rush. Because, whatever the logic, if he gets there and starts taking samples that are more than scrapings for science, if he starts prospecting, or even mining—”
“It’s against Common Heritage law, and we need to bring him back, clean it up.”
Thud. “Right. And that’s why we aren’t going home again any time soon.”
“Correct. You remember there wasn’t the time to upgrade this Mars-run taxi cab to get us there and back. We haven’t the fuel. So we go to this ‘Voga’, deal with Gershon, and the three of us go into coldsleep until we are followed by a more capable ship in a few years.”
Thud.
“Shit,” I said, putting a lot of heft into the word.
“Seconded. So you want to get out of that coffin and get to work? The sooner I get back into coldsleep, the sooner this mission will be over for me...”
I STAYED AWAKE for a month, alone in trans-Neptunian space. That was the fourth month of our twenty-four-month mission.
Then we both slept away much of the rest of the featureless journey. All this was routine. You rotate in and out of coldsleep to save consumables and your own sanity, and focus on the interesting bits.
I was the first to be woken the next time, at the start of our twenty-first month—by which time we were just thirty-some astronomical units or so out from the target. From Voga, planet of gold.
I spent that twenty-first month checking out stuff, and puzzling over Gulliver’s Travels.
I went over the ship from bow to stern, even though I had every faith in our craft, a tried and trusted development of centuries-old technologies. The Reid Malenfant was like an arrow, with a fat blade and sprawling fletches, and a bunch of balloons stuck to the shaft. The “blade” was our living quarters, a roughly conical hab module containing us, our coldsleep pods, and assorted junk, that sat on top of a service module cum lander, which contained the infrastructure of the closed-loop life support system that kept us alive, as well as a propulsion stage and other essentials.
The arrow’s shaft contained our interplanetary propulsion engine, technically known as a magnetoplasma rocket. Our propellant was hydrogen, stored as a liquid in those balloon tanks along the shaft. We had a compact fusion reactor whose energies ionised the hydrogen to plasma using powerful radio blasts—the fletches at the rear of the arrow were radiator panels, dumping waste heat from this process—and the plasma, bearing an electrical charge, was then grabbed by a magnetic field and hurled out the back. The system was mature technology and ran smoothly, and gave us our cruise velocity of five hundred kilometres a second.
As I said, such a ship, with such a performance, purring along, would get you to Mars and back in a few days or weeks. Even the Jovian system, five astronomical units from the Sun, was within reasonably easy reach. But it would take us two years to get to Voga. To get there in a more sensible time, we would have needed a much more powerful drive—a propellant driven directly by a fusion reaction, maybe, or even by matter-antimatter annihilation. Once we had been developing such drives, but progress stalled when the Chaos came, and industry had to prioritise more urgent needs such as food printers—indeed the whole complex of industrial civilisation came close to collapsing altogether. When we came out of that, the will was gone. And that was why we were crawling out to the Kuiper Belt in an Earth-Mars transport.
And hence our enforced layover at Voga, once we got there. Our low exhaust velocity gave us significant problems with fuel loads. To slow down our twenty-six-tonne dry mass from our cruise speed would take nearly twice as much mass in hydrogen fuel. And to accelerate our dry mass plus our deceleration fuel up to our cruise velocity in the first place had taken nearly twice that total in fuel, again. (Talk to an Answerer about the rocket equation.) So we had left Earth orbit with a mighty load of a hundred and seventy tonnes of hydrogen fuel.
But it could have been worse. If we had tried to ship along enough fuel for the return trip too, the fuel load would have been something over a thousand tonnes. You could put together such a mission, though the structural challenge alone was monumental: where would you hang all
those balloon tanks? And indeed, a mission was being assembled right now back at Earth, to bring us home. But such was the urgency to get hold of Stavros Gershon before he did any harm out at Voga that we had had to be fired off on this one-way mission, before the retrieval option could be designed, let alone assembled.
Look, I’m not complaining.
While on the mission, and especially with our temporary status as Prefects, Joe and I had to follow certain protocols. We were volunteers, of course; we didn’t have to be there. You get your Heritage stipend whatever you do, even nothing at all. I wouldn’t have been there at all if I hadn’t basically enjoyed the routine of long-haul spaceflight.
Anyhow, I told myself, the first ocean-going ships to reach the Arctic and Antarctic had used sails. They’d been inadequate for their task too, but their crews had gone regardless. And they had to overwinter, just as we would, in a sense.
For sure, we’d have an anecdote to impress our grandkids.
The work I had to do on the ship was routine. Similarly, my personal needs for sleep, food, exercise were easily met. Eating alone always bores me.
Gulliver’s Travels and Gershon’s enigmatic remarks were a lot more fun to work on. I have always been a cerebral, solitary type. Lock me in a room with a good mystery to solve, a scientific puzzle maybe, and I was happy—and that was pretty much the situation I had landed in here.
And there was a human puzzle too, which would always attract me more than Joe. The puzzle being, of course, Stavros Gershon’s true motivation.
Most Last Small Step voyagers were happy to stick to the rules. They wanted their moment of fame—and it was enduring fame indeed, as once you are the first somewhere, you will be remembered as the first for all time. There were collector types who had been to as many worlds as they could. There had been a few highly publicised races. And so on.
But they stuck to the rules, which fitted the paradigm of our times. You went down, took your photographs, cleaned up, went home, leaving no more pollution than a flag. Not Gershon, though. I looked again at his message loop, at the need, yes, the desperation in his eyes. There was something more he wanted, and he wanted it badly. The trouble was, he wasn’t saying what that was, not yet.
So, a puzzle. I admit that when I had finally figured it out—or at least the Gulliver stuff, and most but not all of it, as it turned out—I couldn’t wait, and woke up Salo a whole day early to tell him about it.
“YOU SEE, I don’t think Swift was describing Mars’s moons at all. And I believe that’s the way Gershon is thinking too. You seem surprisingly grumpy, Joe.”
Salo, still in his soft sleepsuit, a survival blanket around his shoulders, sipping a tumbler of nutritious, nano-infested glop, glowered at me. “I wonder why,” he said. “Get on with it. Swift says they’re the satellites of Mars, doesn’t he? He wrote that book in...”
“1726.”
“And Mars’s two moons weren’t actually discovered until...”
“1877. By Asaph Hall—”
“I don’t care. I thought Swift had always been praised for a lucky guess, at least.”
“Well, I’ve been looking into that.”
“You would.”
“He probably followed a kind of mathematical logic. It was believed that Earth had one moon, and Jupiter four: the Galileans, all that could be seen with the telescopes of the time. So it was logical, in an orderly universe, for Mars, in between Earth and Jupiter, to have two moons. One, two, four.”
“But didn’t he get the periods about right too?”
“Not a bad guess. He has the inner moon orbit Mars in ten hours, whereas Phobos actually takes just under eight. The outer moon took twenty-one and a half hours, whereas Deimos takes thirty hours. The right order of magnitude. He got the distances from Mars more wrong, though: over twice the true distance for Phobos, nearly 50 percent too high for Deimos. Not that he used those names.”
“Will you ever get to a point, Chambers?”
“But,” I went on doggedly, “what Swift did get right was Kepler’s Law of planetary orbits. He understood Newton’s gravitation, you see. So the square of the orbital period of each of his moons is proportional to the cube of the radius of the orbit, just as it should be—”
“He was describing a plausible system, then.”
“Yes. But just not Mars, not the Mars as we know it. And the information he gives us is... selective. Which makes me think he was describing something else. Listen again.” I pulled up Swift’s words.
Satellites... whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost, five; the former revolves in the space of ten hours, and the latter in twenty-one and a half...
“Those are the only numbers he gives. He doesn’t give masses, or absolute sizes—such as the diameter of Mars, for instance. He just gives the timings, and the relative distances of the moons’ orbits and the planet. Which, if you think about it, is precisely the data you’d get from a basic telescopic observation, without any estimate of your absolute distance from the object. Just the size of one element, compared to another.”
He was waking up; he plodded after my conclusion slowly. “So are you saying that Swift is describing another body? Another system, not Mars and its moons? Something that was actually seen by some astronomer before 1726?”
“That’s possible, isn’t it? If such a system had existed, and was close enough—”
“But no such system does exist, or we’d see it now... Ah.”
I grinned. “You’re getting there. Suppose a rogue planet came wandering through the solar system. Sometime in the decades before Swift, when the followers of Galileo were mapping the sky. A one and only pass. You might see the planet, see its moons, measure times and relative distances. No time to get a fix on the true distance, or the diameter of this fake Mars, before it passed back into the dark, not with the technology of the time. Maybe the result was never published properly; the observation couldn’t be repeated, after all—and at the time there were a lot of unreliable sightings, of moons of Venus, a second Mercury...”
“It couldn’t have been too massive, or it would have perturbed the other planets.”
I shrugged. “Small and close would be visible but harmless.”
He nodded. “And so Swift gets hold of this sighting and weaves it into his fiction. He imagines Mars is like this... wanderer. Because, and it’s just a coincidence, the wanderer has two moons, as he thinks Mars must have.” He looked at me. “But now, here we are chasing Stavros Gershon out to some object two hundred AU from the Sun...” He slapped the side of his head. “My mental arithmetic is stuck. Curse you, sleep pod.”
“I worked it out,” I said evenly. “An object with perihelion close to the Sun, aphelion two hundred AU out, would have an orbital period of about a thousand years.”
He nodded. “It’s five hundred years since Swift. So this object, if it exists—”
“Should now be out near aphelion, its furthest distance from the Sun. Two hundred AU out. Just where Gershon has found his Voga.”
He stared at me. “I’d congratulate you on your logic, but I’m afraid I’ll throw up again. Okay, I can just about buy that. But what about all this crap about a golden world? All in Swift too, right?”
“Yes. If you look hard enough.” But I was on shakier ground, and I hurried on. “Look—I said Swift couldn’t give us the absolute sizes of his fake Mars and its moons’ orbits. But we have the orbit timings, and their relative sizes, scaled against the planet’s diameter. And from that you can work out one more number. The planet’s density. Not its mass, its density. Mass per unit volume...”
He was still dopy enough that I had to walk him through the logic.
This time it was about Newton’s theory of gravity, which built on Kepler’s observations. Newton predicted that the period of a moon’s orbit, squared, is proportional to the orbit’s radius, cubed—that was Kepler’s Law—but also inversely propor
tional to the planet’s mass. In this case the orbit radius was given in terms of multiples of the planet’s own radius—and the cube of that is proportional to the planet’s volume.
So in Newton’s equation you know the period, and you have the planet’s mass divided by the volume, which is its density...
You don’t have to follow all that. Working through the math is easier, actually. Go ask an Answerer. Salo didn’t follow it all, not at that moment. But he got the essence: the denser the central planet, the faster those orbiting moons would have to whip around it. And—
“And so we know the density of this Voga. Right?”
I just grinned.
“Well, tell me!”
“Comes out at twenty-four tonnes per cubic metre.”
He was still fuzzy. He growled, “So? Water is around one tonne per cubic metre. Iron is...”
“Nine tonnes per cubic metre.”
“Oh. Which is what rocky planets are mostly made of.”
“Right. Earth’s average density, for instance, is five tonnes per cubic metre. Iron and rock. Whereas gold is nineteen tonnes per cubic metre. Platinum twenty-one tonnes. Look, you can see that Gershon is onto something here. Something exotic.”
He rubbed his face. “Yeah, but what? It’s been a long time since Gulliver. We must know more about this object by now.”
“Sure. Or we wouldn’t be chasing Gershon out here. It was spotted visually by some deep space probe, decades ago. Just another Kuiper object, a sphere, away from the bulk of the Belt. It’s less than a thousand kilometres across. Which gives it the mass of Pluto, by the way, but it’s so massive it has a respectable gravity—about the same as Mars.”
Infinity's End Page 17
