Science fiction has long been fascinated with generation-ship stories in which colonists head for the stars in giant spaceships that will take thousands of years to complete their voyages: ships that become entire worlds to their crews. But maybe we don't need such spaceships. Maybe we don't need to go to the stars. Maybe everything we need is out in interstellar space, waiting for us to hitch a ride.
Or maybe these worlds are already teeming with aliens who've been so long aboard that they see no need for stars, or the dangers that go with them. And that's enough maybes for a whole suite of stories.
Meanwhile scientists are struggling to learn more about the Kuiper belt.
Happily, come July 2015, we'll get a trove of new data. That's when NASA's New Horizons spacecraft will give us our first close-up look at two Kuiper belt objects: the no-longer-planet Pluto and its moon Charon.
I'll write more about New Horizons and Pluto in a future article (including the case for why Pluto, and possibly rogue Plutos far between the stars, might have liquid water). For the moment, one thing New Horizons will do is allow astronomers to tally the numbers and sizes of craters on both worlds. That's important information about the types of objects that have battered them. If there are lots of small craters, then the Kuiper belt is full of kilometer-sized objects, even if we don't know why. If there are mostly giant impacts and a relative handful of small ones, that's further confirmation that the Kuiper belt's progenitor planetesimals were indeed large.
Pluto itself probably won't be all that useful for this because it has a tenuous nitrogen/methane atmosphere that likely produces frost deposits thick enough to wipe out evidence of old craters.
But Charon is too small for even a tenuous atmosphere. “Charon presumably has an ancient surface that's not really been much perturbed for the past 4.5 billion years,” Brown says. “So you can see the cratering record. I think that when you combine that with some of the more intensive studies we'll do between now and then, we'll know the basic outlines [of Kuiper belt history].”
And that, he says, could have broad implications, including shedding more light on our own planet's origins. “We could well be completely rewriting how planets form,” he says.
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About the author:
Richard A. Lovett wears several hats for Analog: not only is this his 37th fact article, but he's also written 35 science fiction stories, plus Biologs and a popular series of articles on fiction-writing.
Outside of the science fiction community, he writes for Nature, National Geographic News, Cosmos, and other general-audience science publications, as well as for an analytical chemists’ magazine. He also writes for running magazines and coaches distance runners, including two women (and possibly a third by the time this article prints) who've qualified to run in the U.S. Olympic Team Marathon Trials.
A former law professor, he also holds a degree in astrophysics and a Ph.D. in economics, and spent years as a food-safety writer and chemical engineering consultant (not at the same time). Find him on the web at richardalovett.com.
Copyright (C) 2012 Richard A. Lovett
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1 en.wikipedia.org/wiki/GerardKuiper.
2 An exact tally is surprisingly hard to find. I've based this estimate on a scatter diagram on Wikipedia: en.wikipedia.org/wiki/File:TheTransneptunians73AU.svg. For our purposes, the point is simply that there a lot of members in each group.
3 An astronomical unit is the distance from the Earth to the Sun, approximately 93 million miles.
4 If this sounds a bit odd, that's because our knowledge of orbital physics has changed in the last few years. That's because, while Newton's laws do indeed predict planetary motion, they do not lead to tidy solutions in a universe with more than two gravitationally attracting objects. (There are a few exceptions for the “three-body problem,” producing stable “Lagrangian” configurations, but these require special conditions.) Not all that long ago, it was the work of a lifetime to crunch the figures needed to track the interactions of just a few bodies, let alone thousands. Supercomputers changed that. What we've found is that the behavior of protoplanets is startlingly chaotic. Rather than orbiting sedately, they interact randomly and soon start flying in all directions—almost like what you'd get if you dropped a bucket of superballs. What this means is that orbits, especially in the early Solar System, are simply not stable. Even large planets can move: a startling result to people raised on an earlier generation of physics.
5 Brown, M., et al, “A collisional family of icy objects in the Kuiper belt,” Nature446, 294-296 (15 March 2007), doi:10.1038/nature05619.
6 Differentiation would occur if the object was large enough to generate enough internal heat to melt ice. Rock would then settle to the center, where it would remain when the ice refroze.
7 The same may also have applied to the asteroids. When we plot their diameters, we find a hard to explain “bump” or excess at diameters of about 100 kilometers. In a 2009 paper in Icarus, a team led by Morbidelli argued that reproducing this bump via asteroid formation models requires starting with planetesimals of at least 100 kilometers in diameter—and possibly bigger. See Morbidelli, A., et al, “Asteroids were born big,” Icarus 204 (2009) 558-573, doi:10.1016/j.icarus.2009.07.011, www.oca.eu/morby/papers/BIG.pdf.
8 Levison, H.F., and Morbidelli, A., “The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration. Nature426, 419-421 (27 November 2003), doi:10.1038/nature02120.
9 Sumi, T., et al, “Unbound or distant planetary mass population detected by gravitational microlensing,” Nature473, 349-352 (19 May 2011), doi:10.1038/nature10092.
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Short Story: A DELICATE BALANCE
by Kevin J. Anderson
Sometimes circumstances require absolute precision—but when humans are involved, precision doesn't come easy.
The test results came back positive. Birenda felt her life change in a cold instant, as if one of the colony airlock doors had burst open and sucked her out into the planet's poisonous atmosphere.
In another time and place, she would have felt great joy to learn that she was pregnant, but this was not old Earth; it wasn't even how the Antorra colony was supposed to be before the disasters happened.
Inside their private family quarters, her father, Walton Fleer, received the results with better grace than Birenda did. “We knew this would happen sooner or later.” The weight of administrative responsibility and the rigors of harsh colony life had aged him greatly, and everyone knew—statistically speaking—he wouldn't live to be an old man. “A new life comes, an old life must go. It's the way of the colony, the only way we can maintain the delicate balance.”
A new life comes, an old life must go. How Birenda hated those words.
“And my name is next on the list.” Walton gave a little shrug, pretending it didn't matter to him. “Only some of us survive, or none of us survive.”
She clung to her father as if clipping a lifeline to his belt. “I never meant to be the one.” Her voice hitched. “I'm sorry.” But she could apologize, and pray, the whole day cycle, and that wouldn't change the fact.
Walton sounded so stoic, as if he were giving a speech to the members of the colony. “This way, at least I'll know I have a new grandchild coming.”
“A grandchild you'll never see,” Birenda said, then clenched her jaw so tightly she thought her teeth might crack.
Pregnancy tests were rarely needed on the desperate colony, since everyone knew the consequences of population growth and took careful precautions. As the current head of the small colony, Walton Fleer had managed to purloin one of the kits from a locked med-center cabinet after Birenda whispered her fears to him. It was just the two of them, counting on each other. After she used the test strip, the older man waited dutifully beside her, kneading his fists together as they waited an agonizing five minutes for the chemicals to work their damning magic. Pregnant.
Walton did not rail against her for being stupid and careless; Birenda had done enough of that herself. Birth-control measures were available to all colonists, everyone knew how to use them, and everyone understood that “accidents” were not acceptable. Each new life was a miracle, a blessing not to be spurned, but for a colony existing on the razor edge of survival, pregnancies must be meticulously planned. When the others in the colony did find out, they would hate her for such irresponsibility, particularly those couples that had already petitioned the colony council to be next in line for having a child.
Her father tried to sound soothing. “You won't show for a few months, so we don't have to do anything yet. Nobody else needs to know. We can figure out what to do.”
Birenda bit her lower lip and nodded, cursing herself for her weakness. “That'll buy us a little time.”
She reached out to embrace her father. In a few months, she could always hope that a deadly accident might happen to someone else, and then there would be no need for drastic action to maintain the delicate population balance. Maybe she could pray for that.
* * * *
The Antorra Colony had started out so well, when measured by hopes and dreams. The original ship carrying two hundred first-wave colonists all bound together by common beliefs had been dispatched from Earth to one of a handful of planets that long-range probes had identified as suitable for Terran life. Although the ten-year voyage had seemed difficult enough, their vanguard ship was much faster than the huge main colony vessel that plodded along behind them. The initial vessel would arrive fifty years before the main group of colonists did.
As true pioneers on an untamed world, the first-wave colonists carried all the basic equipment, survival modules, prefab shelters, seed stock, and embryos they would need to establish a settlement and prepare the world for human habitation. The pioneers were expected to have a thriving colony ready-made by the time the rest of the settlers came. That was the plan.
Birenda had been born en route and was four years old when the vanguard ship reached Antorra. She'd been much too young to understand the miscalculation that doomed them, but she remembered the shockwaves of terror, dismay, and hopelessness as soon as they arrived.
The long-range scientific probes were wrong, miscalibrated somehow; vital measurements had been scrambled by cosmic rays during the transmission, or perhaps the analytical instruments were poorly engineered. Antorra was not fit for human life after all. Although other parameters were within Terran norms, the chlorine concentration in the air was far too high. Not even the hardiest Earth algae could gain a foothold and begin converting the atmosphere.
The pioneers had traveled in space for a decade, with no turning back, only to reach a place where they could not survive.
Captain Tyrson marshaled all the colony equipment and pulled his people together. The habitation domes were self-contained, and the colonists could huddle down and eke out an existence. Antorra would never be the bright new home the faithful pioneers had hoped for, but if they could last for half a century, then the main colony vessel would arrive with all the expansive domes, materials, and scientific experts required to create a rough, but viable colony.
First-wave engineers erected power arrays outside to gather energy from sunlight that filtered through the caustic greenish clouds, but the chlorine corroded the arrays, and they failed one by one. However, with certain austerity measures imposed, an emergency nuclear generator provided enough energy to meet their immediate requirements. For a while, it looked as if the colony just might survive.
Then the corrosive atmosphere ate through the seals in the greenhouse dome, killing seven workers and, worst of all, obliterating much of their seed stock, the only food they could hope for on Antorra. A death sentence.
All of the data had already been transmitted to the main colony vessel that was plodding its way across the interstellar gulf. Among the hundreds of scientists and terraforming specialists aboard the huge vessel, somebody would find a solution in the decades available before they arrived—but that wouldn't help the initial colonists survive in the meantime. . . .
The captain had sealed himself in his main quarters with the full inventory of all their tools, their food stock, their energy supplies, as well as a breakdown of their bare-minimum needs. He did the math, double-checked his results, and could not refute the cold equations.
Now, as Birenda brooded alone in her chamber for hours during the sleep period, she reviewed the analysis and grim rationale that Captain Tyrson had left behind in his video farewell. The recordings were required study for every one of the children who had been born and taught on the Antorra colony.
Captain Tyrson called a special meeting of handpicked individuals from among the colonists—himself and eighteen others. It was an eclectic mix of specialties, and no one could guess why they had been chosen. The tense and curious group gathered in the loading-dock module that contained the machinery, environment suits, and equipment needed for exploring the hostile planet.
Monitor cameras captured the captain's last speech. Birenda had watched it over and over, and it still brought tears to her eyes each time.
As he faced the eighteen men and women he had selected, Captain Tyrson said, “This colony's resources can support—at most—174 people. No matter how we tighten our belts, no matter how we conserve, there isn't enough to sustain more people than that. According to computer models, only 174 can survive until the main colony vessel arrives. The choice is hard: Only some of us will survive . . . or none of us will survive.”
Then he had opened the airlock and dumped the nineteen “extraneous personnel” into the deadly atmosphere, himself included. No one lasted out there longer than two minutes.
In a calm and detailed video message left in his quarters, Tyrson explained exactly why he had chosen those particular nineteen—because their skill sets, their health, their age made them the most dispensable. Birenda's mother was among them.
In the twelve years since Captain Tyrson's brutal decision, 174 had become a sacred number, rigidly controlled. Although the actual minimum number for survival could not be precise, due to individual weights, metabolic rates, or behavior patterns, the criterion had to be absolute so that it could be followed without question. It was the only way they could endure the grim necessity.
When leaving Earth with high hopes, the initial colonists had all expected to marry and have large families, to spread humanity across a verdant new planet. Now that was impossible.
Rigid birth-control measures were imposed and strictly enforced, but the colonists could not outlaw all births, because the Antorra colony needed a new generation, a turnover of personnel to stay alive for the next half-century until rescue arrived—there had to be children, had to be replacements. Each time a colonist died in an accident, one carefully selected couple was granted dispensation to have a child.
In Year 3, when a female chemical engineer developed abdominal cancer from radiation exposure, the colony doctor suggested she might recover with thorough treatment, but the treatment would render her sterile. By unanimous vote—Birenda was seven at the time—the Council decided to euthanize the woman, and she had accepted her fate for the good of the colony. Some of us survive, or none of us survive. After her death, one of the healthy young couples received approval to have a child.
Once the first such decision had been made, the rest became so much easier to accept.
In the following nine years, the Council developed several lists—waiting lists for couples who wanted to have children, and ranking lists of all Antorra settlers prioritized by age and value to the colony. Birenda's father had been an astute colony leader for the past two years, but he was now the oldest member, and his name was next on the mortality list.
It was a delicate balance—174. No more, no less.
And Birenda had gotten pregnant.
* * * *
“How could this happen?” Deputy Bill Orrick pretended to be horrified. “Do we
need to impose mandatory sterilization on all fertile young women except for those approved to breed?”
Her father tried to sound calm and reasonable. “This is our colony's first accidental pregnancy in a decade. Haven't we already taken enough extreme measures?”
Birenda could see the strange smile as the deputy considered the consequences and came to the obvious conclusion. Before she could answer him in front of the Council members, Orrick shot a glare at her father. “You know what this means, Administrator Fleer. I'm sorry, but the list cannot be changed. It's agreed upon by every member of the colony.”
“I know what it means,” said Walton Fleer. “I always knew this day was coming, and I'm content to know that I will get a new grandchild out of it.”
She and her father had kept the secret for as long as they could: Birenda hid her morning sickness and wore looser clothes so the swell of her abdomen didn't show, but it was only a temporary fix. Everything about Antorra Colony was only a temporary fix.
She had considered finding a way to abort the baby, researching techniques or drugs in the colony databases. She had told her father this was the only solution, but he was deeply upset. “I will not stay alive on those terms, at the price of an innocent child. We may have set aside many of our beliefs in order to survive here, but I will not ignore that one.”
Each day, during the dreadful waiting, she had watched engineering teams work outside in the hazardous environment trying to build a new habitation dome out of scrap materials. It was hazardous duty and accidents happened—frequently. A fatal mishap, or even a sufficiently grave injury that warranted euthanasia, would even the numbers, keep the 174, and her father wouldn't have to die so that she could have her baby. Then he could live for a little while longer, be a grandfather, hold his baby grandchild. With the colony's reality, Birenda knew it couldn't last, but everyone on Antorra clung to each day, grasped every moment.
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