Wednesday, April 6, 2011

Go Forth, Under the Open Sky

            The observatory, located at the hub of the ferris wheel-shaped ship, was one of Jase’s favorite places. The weightlessness was easy on his diseased bones and arthritic joints, and children were prohibited. Generation 1 members needed occasional sanctuary from the screaming antics of youth—after all, they had earned it.
            But mostly he enjoyed the observatory because of the view. It was the only room in the ship with windows. Although he had spent his entire life locked inside a ship, Jase longed for open spaces and long vistas. He often wondered what career he would have chosen had he been raised on earth. An explorer, maybe—did that profession even exist anymore?—or perhaps a forest ranger.
            There were two halves to the observatory, one on each side of the hub. The ship rotated about its axis to provide artificial gravity, but the two halves of the observatory did not share in the rotation, so the stars did not appear to move when viewed from it. This was useful for the deep-space equipment that required long exposure times, but it was also convenient for visitors.
            He strapped himself into a seat and rotated it so he was facing in the direction of travel. They were approaching their next planetary system, though Jase wondered whether he would live long enough to see it. Even so, this one was intriguing. The central star, Iasus, was by far the closest to Sol-normal they had encountered so far, and already eleven orbiting planets larger than Mercury had been discovered.
            Iasus was the fourth planetary system the seed ship had visited since leaving the earth system more than a thousand years earlier. For the first 750 years the ship cruised without any crew, carrying frozen embryos and seed stores across the light-years as it searched for a suitably earthlike home. When it found one, the ship began the vivification process that brought Generation 1 into existence.
            Jase had been twelve when they reached their first planetary system. Twelve years old—what a tender age to have to make the life-or-death decision they had confronted! The ship, they had gradually discovered, had made a mistake. Or rather, an error in judgment.
            Before the decision to begin the vivification process had been made, certain data from the still-distant star had been ambiguous. It seemed likely that the fifth-most distant planet would sustain life; in fact, the ship had estimated the probability to be about 97%. However, the chance of finding a more suitable star later before running out of fuel was also estimated at about 97%, making the choice a toss-up.
            The ship had delayed its decision as long as possible, hoping for a resolution, but the probability remained stubbornly at 97%. The longer the delay, the less mature the humans would be when they arrived, and the less capable of doing their part of the work of landing and colonizing. Unless something changed soon the ship would have to pass this system by.
            Then new data came in, bumping the probability up to 98%, just enough to make it worth the risk. The humans would be immature, yes, but if necessary they could bide their time in orbit until they were ready. The choice was made.
            Within a year, after it was too late to reconsider, new data dropped the probability below 75%. And it continued to get worse. When Jase was eleven the ship explained the dilemma to him and his shipmates. The chances now were in the single digits and not likely to change much more. The planet was a scalding, waterless wasteland. Life, if it were to exist at all, would resemble a terrarium in hell—covered, cramped, and heavily climate-controlled for many generations to come.
            When the children met to discuss their options, it had been Jase who pointed out that life on the planet would be much like life on the ship. He argued that he’d rather live out his life on the ship, which wasn’t so bad, really, rather than make a dangerous descent and start all over for the sake of something that, during their lifetimes, would be no better.
            The ship was horrified (or at least it made a great imitation of horror); what of future generations? Life on the ship was unsustainable in the long term. They had plenty of antimatter stores, it was true, and could survive many years in space on the food they could grow or synthesize, but eventually it would run out, and they would die.
            But Jase was persuasive. He argued relentlessly, convincing or wearing down his shipmates one by one, until at last only the ship itself held out. Did it regret waiting so long to begin the vivification process, Jase now wondered? It had volumes of information on childhood development and had apparently been convinced that by age twelve they could handle the decisions they would have to make. Perhaps it never conceived of the possibility that they would decline to stop at all, since that was clearly suicide. Nevertheless the codes by which the ship lived were clear: the choice was the humans’; the ship could only advise.

            “Sleeping again, Jase?” Jase started and looked up in the direction of the voice. Chloe was framed in the doorway, rotated relative to him by about 135°. He swiveled his seat awkwardly around two axes until he could look her straight in the eye, and then smiled.
            “As usual. Any insights today?”
            “Just reminiscing. As usual. What brings you here?”
            “I was looking for you, actually. It seems a potentially minable asteroid has been discovered, and your expertise is wanted.”
            “Humph. Haven’t I spent the last forty years teaching these so-called students what I know? When will they stop needing my expertise?” He unbuckled and launched himself slowly toward the entrance, pleased in spite of himself.

            When twelve-year-old Generation 1 finally made the decision not to land on the planet the ship had chosen for them, they had antimatter stores sufficient to last twenty years, or thirty if they were particularly thrifty. By forgoing the enormous energy expenditure of deceleration they bought themselves a lot of time. Although their speed at 0.4c was not sufficient to bring the stars much closer to them relativistically (distances were foreshortened by only about 8%), they could still reach a number of nearby systems before their fuel ran out. Unfortunately, as the ship repeatedly pointed out, none of those systems looked any better.
            They could improve their odds if they could somehow find a way to mine the system they were passing through for energy. A solar windmill could be grown, for example, to capture the star’s radiant energy, and the ship rapidly came up with a workable design. But that would add only a tiny fraction to their current stores.
            Mining of asteroids could only be done if they decelerated to match the asteroids’ orbits, but that would deplete them of most of their fuel. If there weren’t sufficient raw materials, then that, too, would be a suicide mission. It began to seem as though their only choice was how to die.
            Fortunately the planetary system had a healthy asteroid belt, and spectroscopic analysis indicated a favorable composition. So they set to work identifying an asteroid that met all the needs for a mining operation: appropriate composition, solid rather than a loose aggregate, small enough to have a negligible gravity well, but large enough to be worthwhile.
            The children’s course of study was abruptly changed from planetary ecology to the geology of mining and the physics of producing and containing antimatter fuel. Jase’s interest was in the geology, rather than the physics. He imagined roving far and wide over the surface, exploring deep caves, making discoveries. He also wondered how high he could jump on an asteroid. Could he jump himself into orbit? He was disappointed when simulations showed that no matter how he jumped he would always either drift back to the surface or escape altogether, rather than enter an orbit. Still, gravity so low that you could jump halfway around a world before landing again set his imagination on fire.

            “...evidence of iron-rich veins which may well contain sufficient tungsten for use as an accelerator target. We plan to take additional long-exposure measurements as soon as we can get time on the astrospectrophotometer.” The speaker was Leona, a mining expert and one of Jase’s star students. Given the limited data that was available to them at their current distance of over two light-years, human intuition was as crucial as raw computing power for determining whether they were likely to find the raw materials they would need.
            Jase took a seat near the back, trying not to draw attention to himself. Back in artificial gravity again, his legs trembled as he lowered himself into the chair, and when his legs finally buckled he plopped down hard, wincing at the pain in his spine.
            Leona had evidently just finished presenting her findings on this system’s asteroid belt. Or rather, its outer belt; this system had two. She was now taking questions.
            “The compositional patterns you’ve shown here do not closely resemble those of the previous systems we exploited,” pointed out a young, intense man Jase didn’t recognize. He had risen and was standing near the front of the room on the right side, facing everyone. “Given the great demand for the astrospectrophotometer for more, shall we say, conventional needs, how can you justify using it for your more speculative interests?”
            Leona, visibly angry, took a moment to control her emotions, and then answered calmly, “I justify it on the basis that we need more than one plan at this early stage. We learned from Generation 1 the perils of putting all one’s eggs in one basket, that basket being colonization. Though we all hope for colonization, we have not yet firmly established that Atalanta will fit the bill. When we begin deceleration we should have not one but two fully fleshed out options, because after that we will be irrevocably committed to this one system—it will be too late to think of moving on.”
            Atalanta, the target planet, so dubbed because of its close orbit and consequently great speed, was rated at 0.7-earth normal. It was hot and dry, though mercifully not tide-locked. It had somehow avoided a runaway greenhouse effect and had a full but not oppressive atmosphere consisting primarily of nitrogen. The polar regions contained most of the water so far detected and had a more tolerable climate, and consequently were the current focus for settlement.
            “I see Jase from Generation 1 has arrived,” Leona continued. “Would you care to weigh in on the question?”
            Remaining seated, Jase said, “I couldn’t have expressed it better than you already did.”
            “Everyone knows your bias, Jase,” countered the intense young man, still standing.
            “Excuse me, I don’t believe I know your name...?”
            “I’m Marius, lead botanist.” Like all of the crew he had only a single name. “Perhaps if you spent some time on the colonization effort you’d be more—“
            “I would be very pleased to spend some time with you, as soon as I’ve recovered from my latest round of chemo and I can tolerate gravity again. Thanks for the invitation.”
            “I’m sorry, I hadn’t heard...”
            “Forget it. Leona, I have a question.”
            “I came in late, and I wonder if you could characterize, in a general way, how this system’s asteroid composition appears to differ, as Marius has claimed, from that of previous systems?”
            “Well...that’s a little difficult. I don’t have the data at my fingertips just now...”
            “I don’t need data, in fact data would get in the way right now. Just a general characterization.”
            “Okay, I can try. As you know, we have had the most energy-harvesting success with substrates high in titanium and gold, which tend to be associated with iron-rich bodies. The few measurements we’ve been able to make so far indicate a more silica-rich composition. However, we’ve noticed higher chalcophile concentrations than we’ve seen in any previous system, suggesting some unique chemistry that we don’t have a good handle on yet.”
            “Thank you, excellent.” Jase was getting drawn in by the science, as he always did, and it took his mind momentarily off his discomfort. Higher chalcophile concentration, combined with a silica-rich substrate—what could that indicate? You would expect a higher chalcophile presence in an outer-belt body and a higher silica concentration in an inner-belt body. Could an inner-belt object be ejected from its orbit and collide with an outer-belt body, producing a hybrid? It was feasible, but it should be a rare event.
            “How many different outer-belt bodies have you analyzed so far?” Jase asked.
            “Two, but only one in detail.”
            “Did both of them display high chalcophile concentrations in a silica-rich substrate?”
            “Yes. That’s what we have trouble explaining. I hope you can provide some insight.”
            “I’d be happy to try. If you can set aside some time—give me an hour’s notice so I can medicate—I’ll help where I can.”
            Jase sat through two more presentations, occasionally dozing in his chair. At the break he got up stiffly and hobbled back to his module, popped a tranq, and sank into bed.

            The ship’s first stopover at an asteroid lasted fifteen years. Generation 1 grew up, Generation 2 vivification began as soon as they had dug in to their temporary home, and the first natural births occurred, getting Generation 3 off to a good start. By the eve of their departure their energy stores exceeded by several orders of magnitude what the ship had possessed when it had left earth all those hundreds of years earlier.
            Traveling through interstellar space with a live crew was a different proposition entirely than sending a cold, nearly dead shell across the light-years. The energy needs were split between fuel and life support, rather than going almost exclusively to fuel, hence their range was more limited. They would have to achieve much higher speeds if they were to have any realistic chance of reaching a livable world. Many ideas had been floated, but in the end they settled on a plan to accelerate up to 0.95c, allowing them to cover 150 light-years—half the distance they had already covered from earth—in just over fifty ship years. The energy cost was staggering, almost fifty times what it had cost them to leave earth’s solar system, but there seemed to be no other way to boost the probability of finding a suitable permanent home to acceptable levels.
            Jase knew otherwise. He had read the ship’s logs. For every system that contained even a vaguely earth-like planet there were ten with rich asteroid belts. A more conservative strategy would be to star-hop from system to system, replenishing their supplies at each stop. Such a process could be continued indefinitely, virtually assuring them of eventually finding a highly amenable world.
            The only problem was that none of them would be alive to see it.
            An even more conservative strategy was to stay, spreading out and colonizing the asteroid belt itself. Some found asteroid life not only tolerable but pleasant and argued they should stay. Depleted mining tunnels had been pressurized and converted to living quarters, affording more space and more privacy than had been available on the ship. But the majority voted to strike out again, hoping for a better planetary option.

            Leona finally got the astrospectrophotometer time she had been asking for and used it to scan five more large asteroids, the smaller ones being still too distant to yield much information. The results only added to the confusion, and she scheduled some time with Jase to try and understand them. They met in the observatory.
            “Thanks for coming, Jase. I know it’s difficult for you—“
            “No worries. I wouldn’t miss this; it’s the only thing that keeps me interested enough to forget about cancer for a while.”
            “Any change in the prognosis?” Leona was grateful to Jase for bringing up the subject himself.
            “Afraid not. I won’t know anything for a while, actually. I feel better anyway, now that the chemo’s done. Still some pain, but at least I’m not puking all the time.” The stiff way he moved revealed that his pain was in fact nearly debilitating. He could keep it at bay with medication, but he had kept it to a minimum for this meeting, needing all his mental faculties to be at their peak. Afterwards he could drop a tranq and crash for a while.
            Of the five new asteroids, three showed the same pattern of high chalcophile concentrations in a silica-rich substrate, while one showed a more typical outer-system pattern. The fifth was an inner-system asteroid, which also appeared typical.
            “So four out of six outer-system asteroids show the same anomalous pattern,” Jase observed, “while one shows a typical pattern and the other is ambiguous. Is that right?”
            “Right,” said Leona. “Any ideas?”
            “Several, but they’re all pretty crazy. What have you come up with?”
            Leona smiled. “Always the teacher, aren’t you? Well it appears that there has been a large-scale mixing of the two asteroid belts. One cause could be a close encounter with a rogue planet that mixed up the orbits on its way through the system.”
            “Good. Continue.”
            “The problem is that the asteroid belts are still mostly planar. That could only happen if the rogue planet entered the system along the same plane as the system itself, or else that it occurred so long ago that extra-planar motions were damped out by subsequent collisions.”
            “Which is possible, of course.”
            “True. We’re running simulations now to see whether that scenario would fit the data.”
            “What else have you come up with?”
            “Berek thinks an inner planetoid migrated outward and collided with an outer planetoid, creating the outer asteroid belt. It would take a strange initial configuration for that to happen—usually planets migrate together, and usually they migrate inward, not outward. But it’s not impossible.”
            “Go on.”
            “Then there’s the ‘periodic disrupter’ theory. That there’s a large mass in a highly eccentric orbit that periodically enters the inner region of the system and causes large numbers of inner belt asteroids to be flung outwards to collide with the outer belt.”
            “Good, good. Anything else?”
            “Lots. But those are the most reasonable scenarios we’ve come up with.”
            Jase sat back, steepling his fingers. “I’m not sure why you think my assistance is so important. Sounds like you’re doing good work.”
            “Thanks. But I just have this nagging feeling we’re missing something.”
            “Why do you say that?”
            “It’s just a feeling. You know how when the correct explanation for a phenomenon comes up it just feels right? Like it should have been obvious? I don’t have that. Not yet.”
            “I see. You always did have good instincts, which is something that can’t be taught. Let’s take it slowly. Which of the explanations you’ve given me so far seems most likely correct to you?”
            “The periodic disruptor.”
            “Okay. So what would be some other consequences if that were in fact the correct explanation?”
            Leona thought for a moment. “It would mean that the process is continuing today, so every planet should be pock-marked with craters, even the geologically active ones.”
            “Good. Do you have images of all the planets?”
            “Fuzzy ones. Some of them are shrouded in clouds. The ones we can see have lots of craters, but we don’t know much about their geological activity. Meleager appears to have an active volcano, complete with plume. With the others we can’t tell.”
            “And Meleager has craters?”
            “I...think so. I’d have to check.”
            “Do so. What other consequences would there be?”
            “Hmm. If the periodic disruptor has been in the system a long time it should have cleared out all orbits in resonance with it.”
            “Have you checked for any obvious gaps in the orbit space?”
            “No. It’s embarrassing, but no, you’re right, we should have looked for that.”
            Jase groaned. His back was killing him. He would like nothing more than to continue digging into the problem but the pain was growing too much to bear.
            “Are you okay?”
            “I’m sorry, but I think I have to take a break. This has been very interesting. I hope I’ve been of some help.”
            “You have, I assure you. Can I help you?”
            “If you could find my medicine kit here.” He handed her his bag. “It’s a small faux-leather purse in the top pocket...yes, that’s it. Thanks.” He opened the case and pulled out a pill bottle. “If you could open this...two pills...thank you.” He swallowed them dry, making a face. “I should be fine in fifteen minutes or so. You can go. I’m sure you’re busy...”
            But Leona stayed. She helped him reorient his chair to face their destination star, and he settled back and watched. It was decent of Leona to stick around, and he appreciated that she understood silence was best at the moment. Without the need to speak he could focus on pain management, a subject on which he was rapidly becoming an expert. He systematically explored the stars within his view, checked his pain level, then repeated. After four or five repetitions there was a noticeable diminution of pain, just enough to take the edge off, and he ventured another observation.
            “It might be interesting to find out the distribution of orbital eccentricity in the inner belt. A periodic disruptor should cause a large number of eccentric orbits; a rogue planet visitor, if it was far enough in the past, should not.”
            Leona turned toward him and smiled. “Even in pain you can’t stop thinking. I really admire that about you, Jase. If only...”
            If only he weren’t so frail and useless. If only he had not long since consigned himself to perpetual bachelorhood. If only he weren’t so...inadequate. What-ifs were poison; he thrust aside that line of thought.
            “Thinking is life. When I stop thinking, I die.”
            “I hope you live forever, Jase. Really.”

            The second planetary system the ship had visited was small. The star was only a tenth the size of Sol, and it had only three planets. Nineteen years had passed, and there was some disagreement about whether they should bother with such a tiny system, which, although it housed one potentially viable planet, seemed unlikely to provide a final home.
            In the debate it was the youth who prevailed. Some barely remembered the system they had left, but all were eager for something new, something different than the endless drifting through the cosmos that had characterized their entire lives up to that point. Generation 1 was now well into their forties and showing their age; Generation 2 was at the peak of their powers and, with Generation 3 on their side, had the numbers to carry the day.
            Halfway into deceleration it was abundantly clear that no final home was awaiting them in this system. The crew quickly adjusted to harvest mode, and found an asteroid that met their needs. This time it only took five years to replenish their energy stores, and then they moved on.

            Jase woke from his drug-induced slumber. It was the middle of the night, ship-time, and no one was about. He rose and ate perfunctorily, then took a pain pill and went through his stretching routine. By the time he finished he felt ready to move, so he took a few slow turns around the gerbil wheel and then made his way towards the observatory, which he was sure would be abandoned at this hour.
            He was troubled by Leona’s data. Something about it felt wrong. When she came back with answers to the questions that came up during their last meeting he might feel more certain, but for now he was left with an unsettling sense that they were all missing something obvious.
            A wave of pain overcame him, thrusting him into pain management mode. When it subsided he reviewed one more time the information Leona had related to him: two asteroid belts; mixed outer-belt composition as the rule, rather than the exception; planar orbits; cratered surfaces. What had they neglected to consider?
            Another wave of pain overtook him, doubling him over. Either it was getting worse or his tolerance for the pain medication was increasing. He popped another pill as soon as he was able, and kept himself as still as possible, trying not to trigger another episode. What kind of life was this, not even moving just to try to make it through? He popped one more pill. No life at all, that’s what kind. He counted slowly to one hundred, then two hundred, waiting for the next wave of pain to overtake him. Finally it came, but through a haze; the medicine was working. Now maybe he could think.
            He looked through the tiny windows, moving from one to the next to try to cover as much of the forward view as he could. The outer asteroid belt was just becoming visible to the naked eye as a fine misty arc just a few degrees separated from the star. Soon they would begin deceleration, assuming (as seemed likely) the decision was reached that this planetary system met their criteria for either settlement or refueling. If he could last that long, he would have a decision to make...
            If only he had the data on asteroid orbital eccentricity and gaps in the orbit space. But supposing he did, what would the answers tell him?
            Subconsciously he entered lecture mode. Suppose there were no gaps in the orbit space. What would that mean? For one thing it would impose limits on the orbit of the hypothesized periodic disruptor. For no gaps to be evident it would have to be either a recent addition to the eccentric orbit club, or it would have to have a particularly long period. Either case presented difficulties explaining the prevalence of chalcophilic materials in outer-belt asteroids, since the total number of inner-orbit visitations would be small.
            Okay, then. If there were gaps, no such problems arose. What would an orbital system look like that had a conventional series of roughly circular orbits, plus one large, reasonably close-in, highly eccentric orbit? Such a thing had never been seen before, according to the ship’s reference library. There were doubts as to whether such a system could be stable. Jase thought of running some simulations, but he had a strong suspicion that they would merely confirm what he already suspected: that either the periodic disruptor would be ejected from the system entirely, or that, over time, it would so scramble the orbits of the other bodies that it would look nothing like what they were seeing.
            That forced him to consider Leona’s alternative hypotheses. A one-time rogue planet? Somehow it seems unlikely that a single encounter, no matter how disruptive, could fling so much inner material outwards that a majority of the outer-belt asteroids had been impacted. Migration of a single inner planetoid? It had never been documented before and no simulations supported the idea.
            A diffuse, foggy wave of pain washed over him, demanding his attention but lacking any hard edges. A conviction overcame him that his time was nearly through; the chemo had failed and the countdown had begun. He wondered how long it would take. A week? A month? Maybe he could last a few months. He doubted he’d see his next birthday ten months from now. Call it an even six months to live; how should he spend it?
            He regretted never having left the ship to explore the asteroids they had stopped at. EVA suits were available, but he had been so busy he never found the time to venture out onto the surface and fulfill his twelve-year-old dreams of exploration. Now it was too late, it seemed.
            “Ship, how long until we reach the outer asteroid belt?”
            “We should reach it in roughly one point seven years.”
            Too long. He would never make it.

            The third system the ship had encountered looked promising from a distance of two light-years. Unfortunately, long after deceleration had commenced, the candidate planet was rejected once the ship got close enough to gather detailed data. One problem with a high-speed approach was that the decision to decelerate had to be made before detailed data on the planets could be obtained, and consequently the data was less complete and less compelling. They stopped for fuel and moved on.

            Deceleration had commenced. The ship’s rotation had stopped while it reconfigured itself in preparation. Jase appreciated not having to retreat to the observatory to experience weightlessness, and his bone and joint pain eased. The interior of the living quarters was rotated ninety degrees, anticipating “down” being towards their destination rather than away from the hub. Thousands of thrusters were grown, carpeting the ship’s leading surface as it sped toward its goal. When everything was bolted in place the thrusters were fired up, slowly at first, then gradually ramping up to one gee. The ship creaked and popped, but held together.
            Now there was no respite for Jase; the entire ship was under steady acceleration, and his moaning joints had to support his full weight wherever he went. He ramped up his medication and spent more and more of his time asleep.
            Atalanta was looking more promising. Significant ice deposits had been discovered at the poles, and weather patterns appeared relatively benign. Much of the crew was at work designing a local ecology or investigating terraformation potential for the long term. Leona and her team continued to investigate the two asteroid belts for energy mining.
            The good news for Jase was that, contrary to his expectations, the cancer had been beaten back by the latest round of chemo. Though far from cured, he now was expected to live at least another year, and perhaps much longer. He began to take more of an interest in Leona’s studies, when he felt up to it. She was now lobbying to send a probe to one of the asteroids to gather and return samples. The chemical composition remained mysterious, and Leona felt that some lab experiments were required to fully demonstrate the viability of the mining equipment modifications her team was proposing. It was a tough sell.
            On one of his good days Jase paid a visit to Leona. It had been a few weeks since his last update. There still was no good explanation of the anomalous asteroid composition, and Leona had stopped worrying about it, choosing instead to focus on how they could exploit what was there.
            “Jase, what a surprise. How are you feeling?” Leona beckoned him into her module and indicated an empty seat.
            “Much better today, thanks. If you don’t mind I’ll stand; that’s more comfortable for me.”
            “What can I do for you?”
            “I was wondering if you had any more insights about the asteroid composition.”
            “No, not really. You know that hasn’t really been our focus lately...”
            “Yes, I realize that. I don’t know why I can’t let it go myself, but I can’t. Has there been any additional data that might be related? Anything on orbital anomalies, for example?”
            “Not that I’m aware of. Other than the one the ship announced the other day.”
            “What? I didn’t hear about that.”
            “You didn’t? Well it’s simple enough: it seems our own trajectory has been a little difficult to understand. After taking into account perturbations from the largest planets there’s still a deviation that can’t be explained.”
            “What has been the speculation?”
            “It’s been all over the map. Undiscovered planets, an invisible companion, a giant transparent dust cloud, and even more exotic stuff. It’s probably something simple, though.”
            “Can the ship hear us here?”
            “Yeah. You want to bring it into the discussion?”
            “Yes. Ship,” he said, turning away from Leona and facing the center of the room, “what is the nature of the gravitational anomaly?”
            “The simplest way to describe it is that the star’s mass appears to be decreasing as we approach it.”
            “Which of course is absurd; so the alternative explanation is...”
            “That one or more as yet undetected gravitational sources are causing a net force to be generated along the direction of the star.”
            “And since the apparent force is decreasing as we approach the star—”
            “The mass or masses must be predominantly on the far side of the star from us.”
            “Hmm, that’s interesting. Can we detect any influence on the orbits of the major planets?”
            “Unfortunately we have not been in the system long enough to have observed sufficient planetary movement. The only influence that can be measured is that on ourselves.”
            “Suppose it were a single mass—what could you conclude about it, based on your observations?”
            “Recent measurements suggest that the effect is increasing slightly as we draw nearer the star. If confirmed, that would indicate a mass less than twice as far from the star as we are now.”
            “And we are, what, about 1.5 light-years away now?”
            “1.8 as measured in the star’s reference frame.”
            “Which would make this mass less than 3.6 light-years away.”
            “Any estimate on how great the mass would have to be?”
            “Not larger than 6% of the mass of the star. The closer the mass is, the smaller it would have to be.”
            “Still, 6% is huge! Much larger than any planet. Could this be a binary star system, with a dark companion?”
            “That would fit the data, yes.”
            “Please run some simulations to find out what possible orbits a companion star could have that fit all the data we currently know. Assume all the planets are in stable orbits, but don’t assume anything about the outer asteroid belt.”
            Jase stretched, groaned, and finally lowered himself gingerly into a chair. Turning to Leona he asked, “Is there anything else interesting going on? How is the asteroid mining plan coming?”
            “That depends on what you mean. If you mean, ‘are you making progress on the design?’ the answer is yes; if you mean, ‘are you getting the resources you need?’ the answer is definitely no.”
            “Still having trouble justifying the project?”
            “More than ever.”
            “I’ll see what I can do. I’m sorry I haven’t been more available. I’m told I have more time left than I thought—“
            “I heard! That’s great!”
            “Yes, I suppose it is. I was almost ready to check out, so rejoining life is taking a little adjustment, but I’m coming along. Anyway, as I was saying, I’ll see whether I have any clout left and try to steer some resources your way.”
            “Thanks. I’d sure appreciate it.”

            The long haul from their third stop to Iasus had taken its toll on Generation 1. As they reached their sixties and then their seventies their health began to fail, and many showed signs of dementia. The data was not clear, but it seemed likely that a lifetime of exposure to the radiation of space, despite aggressive shielding, caused cumulative cognitive damage. Some, like Jase, seemed unaffected, but many of the Generation 1 crew were now effectively in their dotage.
            A lifetime spent on the run; that’s how it seemed to Jase. Within his lifetime they were unlikely ever to settle on a planet and build a real home. His childhood fantasy of running through grass-covered fields under an open, welcoming sky would never come to pass. The simple joy of walking out in the open—even if it meant wearing an EVA—was destined never to be his. Unless he could change the terms.
            At age twelve Jase had argued for a different vision, a solution outside the range of anything that had been considered by their designers. With indefatigable argumentation and irrefutable logic he had won over his crewmates to his point of view, and had redefined their mission. He was older now, and the crew was much larger, but maybe he could do it again. Shortly before the Iasus system had been encountered he started arguing for permanent settlement among the asteroids.
            He pointed out that their first stop had demonstrated that life on an asteroid was possible. Furthermore, the ship’s data demonstrated that asteroid belts were abundant; they were sure to come across another within a decade or two. Since they were now a fully-developed community, rather than an assortment of frozen eggs, their interstellar range was diminished; it was unlikely they would find a livable planet within any of their lifetimes.
            Relentlessly he drove home his arguments, and he gained a number of converts. But a community of eighty spanning every age range was not the same as ten twelve-year-olds. Jase won over a substantial minority of the crew, but he was never able to convince the rest that humans did not have to live on an earth replica, but could thrive in the hostile but fertile environment of the asteroids. Once the star Iasus and its planet Atalanta were identified as the next candidate home, Jase’s movement disintegrated.

            Their speed had now slowed to the point where it was measured in kilometers per second, rather than as a fraction of light speed. They had crossed the outer asteroid belt and the orbits of the seven outermost planets and were now approaching the inner belt. Atalanta was visible to the naked eye from the observatory, and many paid a visit just to see it directly, unfiltered through electronic equipment.
            However, whether they would actually land on Atalanta was now in question. They had discovered that Iasus not only had a brown dwarf companion, but also a third companion that orbited them both at the outer reaches of the system, causing perturbations in the inner orbits that had masked any resonance effects in the asteroid belt. With every close approach the inner companion bumped enough asteroids into Atalanta-crossing orbits that a mini-bombardment period followed, adding fresh pock-marks to Atalanta’s surface every few thousand years. Many crewmembers now argued that this made the planet unsuitable for long-term habitation, however congenial it might be in the short term.
            In consequence, Leona’s “Plan B” was now fully funded. An asteroid probe had already been deployed and recovered from the outer asteroid belt, and another was scheduled in one week for the inner belt. Furthermore, the ship’s trajectory was modified to swing it into a circular orbit within the inner belt while the issue was debated, rather than matching Atalanta’s orbit, giving more time for Leona’s team to complete their studies.
            It had been over a year and a half since Jase’s last chemo treatment, and despite the continuing clean bill of health he felt worse. After a merciful respite, the same old aches and fatigue were returning. He was sure it would start to show in the tests before long. Their potentially final destination lay visible to the naked eye, but like Moses he knew he would never enter the Promised Land. It had been a good run, but someone else would have to finish it.
            He hobbled towards the observatory after sneaking out of yet another status meeting. He had begun to lose interest in the day-to-day activities of asteroid research. As Leona’s team expanded and the more challenging issues were dealt with, his participation was no longer so crucial, and his mind drifted while the discussions washed over him. In the observatory he could think and plan.
            He sat down and stared out into space. The bright blob of Atalanta was front and center, but he turned away from the planet and oriented his site along orbital swath of the inner asteroid belt. None could be seen with the naked eye, but his imagination filled in the details. The ship’s trajectory should take them to a close encounter with a small asteroid in about four weeks, and they were already decelerating to match its orbit.
            Jase looked up details on the asteroid. Long axis 8.2 km, short axis 4.6 km, composition estimate 45% silica, 35% iron oxides, 15% magnesium oxides, 10% other, surface gravity 4 mm/sec2. How high could he jump against a surface gravity of only 4 mm/sec2?
            Leona found him later, asleep in his chair. She roused him gently and, when he had difficulty standing up, offered him her elbow, a look of concern crossing her face. Jase smiled and waved off her unspoken question.
            “I’m fine—just stiff. Thanks.”
            “When did you sneak out? I didn’t notice you had gone until the Q&A session.”
            “Oh, an hour or so ago, I suppose. My mind was wandering, so I thought I might as well wander too.”
            “I can summarize it for you—“
            “Perhaps later. I believe I’ll take a nap now.” Declining her proffered elbow Jase shuffled off down the hall towards his module.

            The first deaths occurred during the interstellar journey between their third stopover and the Iasus system. An entire generation had lived out their lives without ever breathing natural air or walking in natural gravity. As the original ten slipped away one by one, Jase made peace with his fate. The diagnosis of cancer surprised him, a little, since the other members of his generation had suffered decline in different ways, but he learned to accept it, grateful that at least his reasoning abilities appeared undiminished.
            When it began to appear that he would not last long enough to reach another planetary system, he was thrown into a deep depression. An entire lifetime spent inside a metallic womb—what kind of life was that? He would not let it end that way, no matter what. He had to find some way out, even if it killed him.

            The asteroid now dominated one entire half of the observatory. The ship was still edging closer, passing by at a velocity not much greater than escape velocity. Its antimatter engines fired short bursts from time to time to counteract the feeble gravity of the asteroid. Jase spent more time in the observatory than ever.
            “We’re just about ready to launch the next probe,” Leona announced, startling him.
            “When do you expect it to happen?” Jase asked, swiveling around to face her. “I’d like to be there.”
            “Tomorrow, 7 a.m. We’re just finishing the final equipment tests today.”
            Jase nodded. “And what do you hope to find this time?” he asked, feigning interest.
            “Sample collection, obviously, but even more important is an on-the-ground survey. We’re finishing testing today on a rover that will traverse the surface over a period of two days. Since it can only cover a fraction of the surface we’ve programmed some smarts into it so it will follow the most promising paths as it roams and gathers data. Fascinating, really; you should see some of the simulations.”
            “I may stop by.” He paused, considering how much he could ask without raising suspicion. “Um...what else are you packing into this probe?”
            “There isn’t room for much else. Everything’s pretty much just attached to a structure housing the thruster. We’re depending on a soft landing, because otherwise everything will just break. There’s no padding and nothing’s enclosed.”
            “Sure, that makes sense. How long will it take the probe to reach the surface?”
            “Just a few hours. You can see for yourself how close it is!”
            “Yes, I can; all I’ve been doing lately is gazing at it.”
            “Gotta go, Jase. Stop by tomorrow and I’ll show you those simulations.”
            “Thanks, Leona, I just might do that.”

            The next morning Jase arose at five, ate a full breakfast, stuffed his pockets with food bars, and made his way to the launch pad. No one was up yet despite the impending launch. The word “launch” was a bit grandiose for the simple undocking operation it referred to. The probe would separate from the ship at a tiny speed of a few centimeters per second, not firing its thrusters until it was more than one kilometer out, and even then just in short bursts to keep it aimed at the landing target. The only interesting part of its flight was the landing, where even the feeble gravity of the asteroid was sufficient to cause damage if deceleration were not carefully controlled.
            Jase donned an EVA suit. Although he had never worn one, he had been practicing with the controls for the last month, whenever he could get a few undisturbed moments alone, and he felt confident he could control it. Its water packs were fully stocked. He checked his pockets for the third time that morning just to be sure the pills were still there. Then he slowly opened the hatch, clambered out onto the probe, closed the hatch behind him, and settled in.
            Even through his helmet the stars blazed in a way he had never seen before. He was in the ship’s shadow, sheltered from the direct glare of Iasus, and had a clear view of the asteroid. Its irregular shape shone with sharp edges and black crevasses, like an oversaturated photograph. He marveled at details: rubble visible in the narrow middle, evidence of impacts, deep shadows and brilliant reflective facets, details piled upon details, a fractal miracle unlike anything he had ever seen shipboard.
            Finally he felt the gentle nudge of dedocking. He wondered whether Leona had looked for him. If anyone bothered to check, his monitors would have confirmed that he had never left his module that morning and was likely still asleep. Eventually someone would discover his carefully planned deception; he hoped it would not be for a while yet.
            An hour passed, then two. He felt the occasional acceleration from the thrusters, though the asteroid appeared no closer. He was hidden from view of the ship, just in case someone tried to watch from the observatory, and consequently the ship was also hidden from his view. He dozed.
            When he woke, the asteroid was noticeably closer. He fantasized jumping to it—it seemed so close—but he knew the feeble gravity would still be sufficient to cause injury or death if he fell from this height. So he waited.
            As the surface drew nearer it slowly stopped looking like a rock just out of reach and started looking more like a barren, rocky landscape with a horizon. His anticipation grew as the rock drew closer, closer, almost close enough to touch—but no, it must be farther than it appeared since the probe had not commenced deceleration yet. He forced himself to be patient.
            At long last the thrusters fired up, seemingly just meters from the surface. Jase watched, enthralled, as the surface drew ever closer—impossible that they had not landed yet!—and still they continued to descend. Pebbles grew to rock size and then boulder size, until he lost all confidence in his ability to judge distance. Only when the thrusters threw dust up from the surface was he confident that he had finally arrived. Unable to resist any longer, he leapt free of the probe.
            Unaccustomed to microgravity, his leap carried him upward, away from the surface, and he started to tumble. He laughed in delight, realizing his error, and wondered how far his over-enthusiastic leap would carry him. He tumbled end-over-end five, six, seven times, before the surface drew near. His head hit the surface first and he bounced back up with reversed spin, completing three full rotations before brushing the surface again, this time with his feet. In all he touched down five times before managing to slide/roll to a stop, laughing the whole time.
            He paused for breath, took a drink of water, and looked around. No landscape in any movie resembled the scene before him. His leap had carried him far from the ship, which was now hidden from view, although dust raised from its landing shown in the light of Iasus above a low hill.
            How far could he leap, if he just sprang from where he stood? How high if he leapt straight up? How many hops would it take to circumnavigate the whole asteroid? He had some idea, having queried the computer (obliquely, so as not to divulge his plans); but he looked forward to trying it out.
            He took a tentative step, lifted off the ground, over-rotated, and landed on his belly fifteen meters away. It would take practice to learn how to navigate this surface, but he had time. He had the rest of his life.

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