Convergence, Part Three

3 11 2011

And so, the planetary systems of the two Main Sequence stars of Alpha Centauri came to settle into a tenuous equipoise. Proxima Centauri, Fram, Belgica and Maud, their moons, the asteroids of the inner system and dwarf planets and KBOs of the outer system, circled about Alpha Centauri A and B for four and a half billion years. So too did Alpha Centauri A and B circle about the Milky Way as the entire Galaxy spun like a pinwheel, its spiral arms trailing away from the direction of its rotation. And the Milky Way interacted with the Local Group, and was pulled with the accelerating expansion of the Universe.

It was a stasis of silent, sure, sweeping movements.

In that silence, a narrow and forever imperilled form of life emerged. The impact of comets and carbonaceous chondrite asteroids gave the moon that humans would one day call Amundsen a burgeoning atmosphere, and, with that carbon dioxide, carbon monoxide, methane and ammonia, deposited organic compounds, long-chain hydrocarbons and amino acids. While the planets and moons spun in mean motion resonances, these compounds evolved into a primitive life that consumed carbon dioxide and hydrogen and produced methane.

These methanogens, exceptional and precious and delicate though they were, would never look at the stars and give them names; would never write equations to explain the motion of the planets; would never manipulate the fundamental building blocks of the Universe and use that knowledge to propel themselves across the gulf between stars. For two billion years these methanogens evolved in complexity and function from those cometary hydrocarbons – and then their evolution plateaued, unable to expand from their niche. Fragile fronds caressed the thin air of Amundsen with neither mind nor purpose.

When Amundsen’s surface was shattered by a devastating impact, these methanogens rode debris to the surface of Fram, and, in the overabundance of Fram’s dense carbon dioxide atmosphere, thrived and exploded in numbers.

By contrast, the life that had evolved on Earth was diverse and abundant. It had likewise taken billions of years to evolve, but had done so in an environment of plentiful oxygen, which readily bound with the structural molecules of living organisms – carbohydrates, proteins – and, as an oxidiser, was an energetic component of cellular respiration. Fuelled by oxygen and liquid water, simple cells blossomed over almost four billion years into multi-cellular life; and, in a burst of less than half a billion years, arthropods, fish, plants, and insects appeared; and then, over another 150 million years, reptiles, mammals, birds. After a series of extinction events and periods of climatic change, humans appeared, roughly recognisable after 4.2 billion years of evolution, and certainly within the last 200,000 years as the species that would spread among the stars.

In the space between chords of the musica universalis, humans began to communicate and share knowledge, and to congregate in settlements and farm the lands around them; through agriculture they developed empires and republics and began to speculate about the Universe in which they had evolved. In a flicker of time imperceptible to the patient stars, humans spread across the face of and came to rapidly dominate their planet, first split and then fused the atom, walked on their Moon, developed radio telescopes and studied the stars. As they did so, humans imparted upon the Universe both mind and purpose.

They searched for other worlds like their own. At first they listened to the stars for radio messages, assuming that life had evolved elsewhere as humanity had, and that this life would communicate in the same way that humanity did. They then used increasingly sophisticated technology to monitor the brightness of stars, watching for the transit of planets across the face of those stars; measured the movements of those stars to determine the gravitational influence of large planets upon their star; and, with orbiting space observatories, developed telescopes that could eventually resolve individual planets light years away.

Despite their relative proximity to Sol, Fram and Belgica evaded easy detection. Both were small planets, and many of the methods were biased toward the detection of large gas giants. Belgica orbited close to Alpha Centauri A, and was, at a distance of over four light years, indistinguishable from the light of its parent star. And Fram’s slow, elliptical orbit did not frequently transit the face of Alpha Centauri B – and, when it did, it did so quickly, as Einstein had theorised of an object that moved deeper into the curvature of space-time created by a massive body.

Nonetheless, observations of other stars encouraged humans to believe that small, undetected worlds orbited their nearest neighbours. They sent sophisticated, robotic probes to the closest stars, even as they exploded in number and expanded from their damaged homeworld to colonise the nearest planets and moons of their solar system.

Thus, decelerating from nine-tenths light speed, a robotic mind appeared in the Alpha Centauri system, and reported to the distant minds that had evolved in nearby Sol. This probe noted Fram, noted also its atmosphere and magnetosphere, concluded that human settlement would be possible upon its surface, compiled a report detailing these conclusions to relay to Earth. And with the receipt of those conclusions, two separate star systems – which had, perhaps, in the distant past formed from the same molecular cloud, but which had developed in vastly divergent ways – enjoyed the beginnings of convergence.

Alpha Centauri A and B had not completed two orbits of their mutual barycentre in the time between the arrival of the first, primitive, crackling radio signals from Sol and the arrival of the first interstellar starship. Immediately, the colonists borne from Sol by that ship went to work making Alpha Centauri their home. Intelligence evolved of another star, but an intelligence nonetheless, came to explore and appreciate Fram. Philosophers among those colonists would ask whether Fram had even existed before colonisation, without a sentient, rational mind to observe its orbit, the movement of regolith across the duricrust, the disintegration of Amundsen.

And, then, the life which had come so recently to Alpha Centauri discovered the life that had in so limited a fashion evolved there. At that point, two divergent paths taken by the Universe toward the emergence of complexity, separated by five billion years and four light years, converged…





Panspermia

26 04 2011

Dozer

“The Remokon-90 “Dust Devil”, a quad-tracked pinnacle of autonomous microwave-grading technology, ushered about a new age in what had been previously been labour-intensive and dangerous expansion efforts by the colonists of Fram.  Fed telemetry and geological scans, the Dust Devil worked around the clock turned vast tracts of uneven lunar terrain in smooth, glass-like foundations.  The Remokon-90’s onboard computer could be accessed and remotely controlled, but due to its rugged performance and impeccable results, many of Fram’s large-scale terraforming become the realm of robotics.  Thanks to the Remokon-90, any project involving automated machinery was henceforth affectionately known as “the devil’s work”.

Chesney bounded across the surface of Amundsen in long, loping strides.

Both stars had set, but the light of half-illuminated Fram lit the surface of the moon. It was a strange, muted light, a light that evoked childhood memories in Chesney of the thick smoke of wildfires and the twilight of a sun choked by ash and soot.

To her right was Wisting Base and, beyond that, the straight shadow of a rille defined by its far horst. Rising over these was the crescent of Fram and, curving around the edge of the disc like the bow of a parenthesis, the highlighted arc of the planet’s ring.

As Chesney looked into the light cast from the ring and planet, the regolith which covered the visor of her helmet caught the light. She reached for the soft-bristled brush hooked to her belt; she could not easily brush the particles away with her glove without scratching away the visor’s protective coating.

Ahead of her was the Dust Devil, a ’bot the size of a tank, motionless and dark.

Chesney worked her way toward the Dust Devil parallel to the runway. There was little to this runway, yet – maybe a hundred meters of glazed regolith. This glossy, dark grey path stretched past Wisting Base and ended at a point beneath the Dust Devil. Chesney carefully loped around the recovery equipment for the CATOBAR system: the cylindrical shapes of friction brakes and several coiled arrestor cables. These lay assembled to the side of the runway, and some pits had been dug for the brakes and their motors; but the recovery system was not yet ready to be installed.

“What do you see, Chesney?”

Chesney winced. She looked over to Wisting Base, watched a rover move over the far rille toward the collection of pressurised cylinders, imagined her mission commander watching her on the monitors of the control room.

Martinet.

“I can’t see anything moving.”

Which wasn’t entirely accurate; regolith cast up by the Dust Devil was still settling on either side of the vehicle, falling in perfect, slow parabolas in the moon’s negligible gravity.

“I’ve tried remotely resetting the firmware,” the voice in Chesney’s earpiece stated. “Still getting the same error.”

As Chesney approached the Dust Devil, she saw that the grounding pitons had fired: at points along the length of the vehicle, wires had shot from the Dust Devil into the lunar surface.

“The electrostatic pitons have fired,” she reported back to control.

As the Dust Devil ploughed through the dry regolith it built up a significant tribolectric charge; insulted by the regolith and existing in a vacuum, this charge could not be easily grounded. When in standby mode the Dust Devil deployed these pitons to discharge the electrostatic build-up into the bedrock, where there was a higher proportion of conductive iron.

Nevertheless, as Chesney reached out to place gloved hand on the vehicle’s caterpillar track, there was a brief arc between her hand and the dusty track. She instinctively pulled back her hand.

It took a moment for her suit’s systems to respond, and, during this time, the mission commander’s voice was lost in a wash of static.

“I’m fine,” she said.

She ran her hand over the rear fantail, a bridge suspended between the larger rear caterpillar tracks in which were installed a series of magnetrons. Chesney pulled down a hatch that revealed a hibernating terminal; she awoke this terminal and established a wireless connection with her tablet. She immediately began to run diagnostics on the magnetrons.

“Start with the magnetrons,” the mission commander instructed. “Start with a series of diagnostics.”

Chesney rolled her eyes but held her tongue.

Three rows of magnetrons pointed downward from the Dust Devil’s fantail, and these fired microwave energy into the regolith beneath. At the right power and frequency, these microwaves sintered the regolith and fused it into a half-meter thick seam of lunar glass. This glass was like an artificial basalt, and would, once complete, provide a good foundation for Wisting’s landing strip.

The process relied upon the high level of iron in Amundsen’s otherwise silicate regolith. Deposited here by billions of years of micrometeorite impact, these nanometer-scale beads of pure iron efficiently concentrated the Dust Devil’s microwave energy and heated up the surrounding silica, sintering this loose dust into large clumps and, eventually, solid structures.

Where the Dust Devil had inexplicably halted its programmed sweep, the sintered regolith was thin and cracked easily beneath Chesney’s shifting feet.

“I’m getting nothing unusual from the magnetrons,” Chesney reported. “I’m leaving the system to run a clean-up, but the diagnostics showed nothing.” She clipped the hatch and precluded what she knew would be her commander’s next comment. “I’m heading forward to inspect the dozer and guidance systems.”

The Dust Devil had four large tracks arranged in two sets of two. Set between the forward tracks was a simple dozer blade that levelled and compressed the regolith before it was sintered by the microwaves. Above the dozer was an elevated fin that resembled the twin tailbooms of an aircraft; within this blade were the Dust Devil’s guidance systems: ground radar, forward-looking infrared cameras, electromagnetic and visual spectrum sensors, and path planning intelligence.

Here again Chesney ran a series of wireless diagnostics. She accessed the firmware’s log, and found the same error message as that relayed to the control room.

“Yes, that’s what I’ve got on this end,” the mission commander dryly noted.

“It’s like it’s gone into sleep mode.” Chesney placed her tablet delicately on the upper surface of the guidance fin. “Can you check the program logic from there? Under what criteria would the Dust Devil shut itself down?”

“Mmmhm. While I’m doing that, check the dozer blade.”

With some difficulty Chesney crouched on one knee, bracing herself against the caterpillar track so that she didn’t bounce off the regolith in the low gravity. Like a ship riding a bow wave, the angled dozer blade had ploughed deep into the regolith, and banks of dust had piled on either side. Within these piles there were a few larger, brecciated rocks, but none large enough to halt the Dust Devil.

Chesney absentmindedly picked up one of these larger rocks; saw that while it was fractured it was not a breccia at all; realised that it was striated, igneous basalt. She frowned. Intersecting the banded strata, however, Chesney noticed an imperfect but regular zig-zag; she held the rock up to Fram’s light and saw that these lines were impressed into the rock.

“Oh my God,” she whispered.

Chesney slipped the rock into a sample bag on the thigh of her suit, excitedly ran her fingers through the regolith around her. She found a number of striated basalt pieces, each with the same faint impressions. Chesney’s heart thumped. They looked like adpressions. Common plant fossils. And the shape of the fossils reminded her of the anaerobic methanogens on Fram.

“Those shutdown protocols,” she gushed excited into her mike, “do they include detecting something…biological?”





Not Because They Are Easy But Because They Are Hard, Part Two

9 02 2011

Spread across the ridge was Wisting Base: a handful of brightly coloured, connected cylinders huddled together on Amundsen’s surface. The main base was a muted grey, dusted in moondust. Separated from the modules were a collection of scientific stations; these were wrapped in reflective yellow foil that shone in the sunlight.

There was a habitat module, the largest feature of the base. After the module carried by Wurundjeri had descended to the surface, the crew disconnected the two ends and – using rovers – dragged those ends apart. In the space between was erected a thick, pressurised tent, girdled by ribs like a concertina. From the ribs, cables were fastened to pitons driven into the surface. Now the entire module was perhaps fifty meters long, and contained the living quarters, CLLS system, and workshop. A high-gain dish rose from one end and faced Fram.

At one end of the habitat was an airlock with a ramp leading down to the surface. Layered across the ramp was a sheet of moondust and, where the ramp met the surface, the thin regolith had been disturbed and the pale rock underneath exposed. Flanking the airlock were two smaller cargo pods, their caps painted yellow, solar panels atop their upper surface. Scattered seemingly at random around the habitat were a number of smaller modules, connected to the habitat by pressurised passageways. These smaller modules were crammed with supplies, equipment, instruments. Strips of solar panels again covered their upper surfaces, and small portholes studded their sides.

Several rovers were parked in the lee of one such equipment module; some pointed toward the habitat and others away, one was parked at a slight angle, and trails of lighter regolith snaked away from the parking lot. Scattered not far from the rovers were half a dozen prefabricated sheets, left over from the assembly of the base and discarded.

A hundred or so meters from Wisting Base was the Ascent/Descent Stage. Radial lines spread out from the landed stage, like the streaked ejecta of a ray crater – here the descent engine had blasted away the regolith. Two hemispheres of the payload shroud were abandoned on either side of the lander, and a generator was connected to the upper ascent stage. The airlock door remained open.

Fram dominated the sky above Wisting Base. The brown-grey northern hemisphere of Fram filled the sky, from the horizon to zenith. The surfaces of the two worlds were so incredibly close, and from the smaller Amundsen, it seemed another world was inverted and folded back to form a ceiling. Fram’s hemisphere visibly curved and dust storms moved elegantly across its face. The rising and setting light of Alpha A and B picked out the craters strung across Fram’s northern hemisphere, and at night the lights of the Colonies and Port Mayflower could be seen.

Rising from Amundsen’s horizon to meet Fram was the inner ring, separated into two bands by the Sverdrup Division. Occasionally, Sverdrup appeared and slowly worked its way across the sky; this was an illusion, for it was really Amundsen that lapped the slower Sverdrup.

And, every few hours, Wurundjeri swept across the sky – now composed solely of the spent FDS and the Greenglass, connected by the needle-thin central stack…

 





Not Because They Are Easy But Because They Are Hard, Part One

7 02 2011

Wurundjeri was assembled at the LFO Assembly Station in Fram orbit.

Her various stages were pieced together at Port Mayflower; like the legs of a spider spinning a lengthening lanyard, zero-gravity cranes connected each module with the next and the whole vessel extended from Wilbur. From Port Mayflower she was slipped into an elliptical orbit; around her were the various components and modules, pushed about by Grapes and orbiters, that constituted LFO Assembly Station.

It was a pencil-thin stack of components. Cylindrical modules ran the length of a core of scaffolding; some of these modules were connected at right angles to the central stack. Flaring from the flanks were the dragonfly wings of solar panels. Wurundjeri was an asymmetric, delicate, functional design.

Some of the modules were constructed on Fram’s surface, and were too large to send into orbit using the space elevator. These modules were launched using rockets: heavy lift vehicles adapted from those boosters we had used to send our orbiters into space before the arrival of Mayflower. The launches were spectacular, dreamy – voluminous, grey-white HLVs balanced on a tongue of fire and smoke subdued by the thick atmosphere of carbon dioxide. The Fram Departure Stage, Ascent and Descent Stages were lofted into orbit in this manner, in three separate launches over the space of six weeks.

The FDS was at the stern of Wurundjeri. This was a fifty ton, cylindrical module wrapped in solar panels that flared at its end to shield the ship from the engine exhaust. In its base were mounted three small drive nozzles, which drew upon forty tons of propellant stored within the FDS. At the other end of the module was the stage docking system, which connected to the central stack.

Clustered around the scaffolding that was the central stack were various mission modules. There were pressurised logistics modules, containing supplies and equipment for the lunar mission; habitat modules to form the core of a lunar base; and cargo landers to deploy these modules safely to the surface. These modules were arranged in two rows along each side of the central stack, nose to tail, their sides pressed up against the stack. Eight sets of solar panels were positioned perpendicular to these modules. These two groups of four panels formed the Y axis of the ship, like dorsal and ventral fins, while the mission modules formed the X axis.

Toward the bow of Wurundjeri were two more modules, each smaller than the various cargo and habitat modules. These were the combined ascent/descent stages, huddled together in a protective sheath, and the crew transportation vehicle. Both modules were set into the central stack along the X axis and thus in line with the rows of mission modules, but they were connected at a perpendicular angle, so that their noses nestled into the central scaffolding.

The Ascent/Descent Stages were simple vehicles, not essentially different in purpose and execution to the earliest of man’s lunar modules. The protective sheath was mounted high up on the descent stage, such that most of the descent stage was exposed. There was a single, throttleable engine at its base and a grid of manoeuvring thrusters around the cylinder. There were five legs mounted in a star around the circumference of the cylinder that would deploy prior to landing. Between these legs were solar arrays. Upon the power of this stage would the entire module make a controlled descent to the surface of Amundsen.

Sitting atop the descent stage was the ascent stage, a large, bulbous sphere. This sphere contained the crew cabin and a separate air lock from which the crew could egress to the surface. At the north pole of this sphere was a docking port, which connected with the central stack; at the south pole there were four, bell-shaped engines. Feeding these engines, mounted one atop the other, were spherical propellant tanks. While the Wurundjeri remained docked at Port Mayflower, the entire ascent stage was encapsulated beneath the chequered payload sheath.

The Crew Transportation Vehicle was the name given by mission control to the orbiter attached to the Wurundjeri, the David Greenglass. The CTV would ferry the crew to Wurundjeri, and remain in orbit with the central stack after the mission modules and A/DS descended to the surface.

It had taken almost two months to assemble Wurundjeri. As she prepared for her mission to Amundsen, her hull was painted in alternating bands of light grey and black, and the designation of each of her modules stencilled in white. The last equipment and propellant stores were shipped up from the Colonies, and the crew prepared to step onto Amundsen…





Emergence, Part Two

2 08 2010

And so, Alpha A and Alpha B grew from T Tauri stars into Main Sequence stars. Their stellar winds weakened. The gas and dust of the protoplanetary disc dispersed as these gentler winds scattered the remnants into interstellar space.

As the dusty veil was brushed aside, a crowded solar system was revealed. Planetesimals without number looped through the system. There were asteroids, small and dark, and planetary embryos, each the size of a small moon. The total matter of more than a dozen Fram masses existed in this period of planetary formation, swimming in eccentric orbits.

Some bodies were drawn together by their mutual gravities, and accreted into larger objects. But many others were accelerated by the revolving, twin stars, or by the weak influence of Proxima, or by interaction with the orbital resonances of larger embryos. When these hastened planetesimals collided, they shattered spectacularly. More planetesimals, laboriously accreted over millions of years, were torn apart by the competing gravities of Alpha Centauri A and Alpha Centauri B.

For tens of millions of years these bodies glided through the system, were agitated by their parent stars, were drawn together or smashed apart. It was chaotic, violent, an interplanetary melee – a dance of mathematics and mass and resonance. Humans would later lend this meaning and call it the musica universalis.

Fram and Belgica grew from this churned belt of debris. They were probably the largest of the planetesimals of the Alpha Centauri system, although they were neither unrivalled nor alone. During the latter part of the first 100 million years of planetary formation, while its orbit was still highly eccentric, Belgica smashed into one of its largest neighbours. The impact was cataclysmic, perhaps the most violent of the system: its outer envelope of mantle and crust was blasted from the core, and the young planet lost much of its mass.

Yet it was this collision which probably bound Belgica to Alpha A. Instead of forming into a moon the way that Amundsen had formed around Fram, the material ejected by the collision crowded about the core of Belgica and collected in the wake of its orbit. This area of dense, ejected material pulled at Belgica with a weak but growing gravity. Over many more millions of years, Belgica’s eccentric orbit was slowed, and it fell into a more circular orbit of Alpha A. After billions of years, this material accreted into the misshapen lump that we now called Maud – Belgica’s smaller twin, trailing sixty degrees behind Belgia’s orbit in the Alpha A-Belgica L5 point.

It was not likely that Fram and Belgica formed around the same star. There was probably insufficient protoplanetary material around each to account for the mass of both planets; moreover, their competing gravities would have profoundly affected the development of both. More likely, Fram formed around Alpha B, and for the first 100 million years it was pounded by impacts as its greater gravity drew in the smaller planetesimals around it.

But not every planetesimal interacted with Fram in such a way as to be drawn toward it. Fram scattered many smaller bodies inward of its orbit, and exchanged angular momentum with these scattered bodies such that its orbit, little by little, was cumulatively drawn outward from Alpha B. Fram’s already eccentric orbit grew into a lengthening parabola that became more pronounced as it scattered more and more objects. After hundreds of millions of years, Fram’s aphelion drew farther and farther from Alpha B, until it began to be affected by the gravity of Alpha A; the aphelion of Fram’s orbit was always drawn toward Alpha A as it too rotated about the system barycentre.

For the next four and a half billion years, Fram’s wobbling orbit scattered other objects orbiting Alpha B. Its gravity distributed thousands of asteroids, comets and planetesimals outward into a sparse scattered disc. It trapped nearby asteroids in its Lagrange points. And Fram captured Sverdrup and Nansen, bound these small asteroids to its gravity well, and made them its moons.

The captured moons became gravitationally tied to Amundsen, and were forced into mean motion resonances. It is not likely that every object captured by Fram’s gravity fell into these resonances; Fram probably once had many more moons, in disordered, elliptical, highly eccentric orbits, which were lost to the gravities of Alpha A and B when they did not fall into resonance with Amundsen.

From this multiplicity of simple interactions, an elegant yet complex pattern emerged.

Through interaction with and ejection by Fram’s gravity well, perhaps ninety percent of the mass remaining after the earliest period of planetary development was pitched outward from the inner system and formed into the scattered disc. Fram’s eccentric orbit oscillated and was smoothed through these interactions, as the system sought to conserve angular momentum. In the absence of gas giants like Jupiter, Fram acted to clear much of the Alpha Centauri system of the remnants of the protoplanetary disc.

Yet Fram was never alone. There was no peak period of bombardment as in the Sol system – impacts were ongoing, a geologically regular occurrence. Fram was weathered by constant bombardment, craters overlaid with craters, mountain systems formed not through tectonic movement but the terrific force of impactors. Carbonaceous chondrites, lost in trans-solar orbits, and cold scattered disc and Oort objects, disrupted from their lonely exile by the passage of Proxima: the impact of these bodies over billions of years gave Fram its thick atmosphere.

Most recent of the large impact events was the collision that created Fram’s ring system. The impact had fractured Amundsen’s crust and pushed the moon beyond its Roche limit. The moon had been disintegrating for millions of years, and would continue to disintegrate for millions more. Tidal stresses continued to break apart the moon and spread its debris into a thickening ring.

The Alpha Centauri system had been shaped for five billion years. Volatile bodies had been distributed into a distant, scattered disc. Silicate asteroids had fallen into Fram’s Lagrange points, or into orbital resonances that kept them far from the planet. The system had fallen into equilibrium, and was as stable as it would ever be; now it was the turn of its recent inhabitants to shape this star system…





Selenography

1 03 2010

We looked once more to the sky.

A team from Alpha-1 had made the elevator trip to Port Mayflower. From the observation deck they enjoyed the vertiginous view of Fram spread across the floor of space, and part of the ring slicing toward the horizon. They were looking west, and Amundsen had hours before risen from that horizon. Now it lay above the curve of Fram’s atmosphere, strung along the ring like a bead on a rust-red string.

Fram was a small world; only five and a half thousand kilometres across, not much more than forty percent the size of Earth. But like Earth, Fram had a relatively large moon. Amundsen’s irregular shape was about one thousand two hundred kilometres across, similar to the size of Quaoar or Charon. As Luna was to Earth, so Amundsen was approximately twenty percent the size of Fram. The entire Fram system, planet, ring and moons, would fit easily in the gulf between Earth and Moon.

The experts on Port Mayflower delicately pointed out that we had yet to visit any of the moons. Much of our knowledge of the satellites of Fram had been garnered from observation – by the probes which had visited the system before we had even left Sol, from the Quoqasi as we arrived, or by the orbiters since Planetfall. Some of our knowledge came from the ring system itself. The components of Fram’s ring were pieces of the disintegrating Amundsen, and we had spent weeks crawling over the surfaces of the larger pieces and moving them into safer orbits. There had been some room for science.

“The Fram ring was a good place to start our study of the three moons,” one selenographer explained, and then launched enthusiastically into an explanation.

It was a thin ring; it was about a meter thick, and it was not very opaque. The ring extended from a thousand to six thousand kilometres above Fram’s equator. Our orbiters had spent most of their time in the thousand kilometres beneath the inner ring, that part of the disk closest to Fram. The particles which composed the inner ring were no more than a meter in size, although there were some larger pieces, all of which had been tagged with transponders during the first three months after Planetfall. These larger pieces came from closer to the orbit of Amundsen.

The inner ring was divided from the outer ring by the Sverdrup Division, a sharply defined gap of around four hundred kilometres. The Division was caused by the orbit of Sverdrup, the closest of Fram’s moons, which orbited entirely within the Amundsen ring. Sverdrup was the first of Fram’s shepherd moons; as Sverdrup swam through the ring material on its orbit, its gravity cleared a path through the ring.  Material that drifted into this gap was deflected back into the ring by Sverdrup’s orbit, or accreted onto the mass of the moon.

The Sverdrup Division was not entirely empty. There was a thin, central ringlet which shared Sverdrup’s orbit. This ringlet was knotted by spiral density waves: short, horseshoe-shaped oscillations caused by the resonances of the orbits of Sverdrup and Amundsen.

The selenographer continued. “We really learned a lot about the composition of Amundsen while we were wrapping reflective blankets and installing rockets on the surfaces of the ring bodies.”

The pieces themselves were mostly silicates, a much higher proportion of silicate to iron than we had expected. What iron had been found was in the form of oxides, which explained the reddish colour of the ring. The ring possessed its own sparse atmosphere, only microns thick, of molecular oxygen, hydrogen and even hydroxide. The existence of this atmosphere suggested that the ring once contained quantities of water ice; ultraviolet light from the twin stars had broken down the water ice into its constituent elements.

“And that’s representative of Amundsen?”

“Yes and no.”

When we looked at Amundsen, much of its composition suggested an early bounty of water ice. Spectroscopic studies had shown a rather typical proportion of iron to silicate; moreover, the iron was contained within oxides. UV spectra showed more detail. There were hydrated silicates, which bore magnesium and iron; hydrogen sulphates; sodium sulphates; cyanogens; and carbon dioxide and sulphur dioxide, frozen onto the surface. But the only ices which now existed on Amundsen’s surface were carbon dioxide and volatile ammonia ices; the early water ices suggested by the ring and by the presence of so many sulphates and oxides had long since gone.

The selenographer explained how the water ice might have vanished. It really depended upon which model proved correct to explain the formation of Amundsen. If Amundsen had accreted in orbit of Fram, as the Galilean moons seem to have in the orbit of Jupiter, then it was possible that the surface water ice had simple sublimed under billions of years of ultraviolet light from Alphas A and B. Amundsen lacked any magnetosphere or atmosphere to protect the water ice from the stellar wind.

“There are a number of problems with this hypothesis,” the selenographer continued. “First, if the ice had sublimed, we’d expect to find traces of an atmosphere on Amundsen like we do in the rings. We don’t. A lot of it would escape into space, but not all. The presence of molecular hydrogen and oxygen in the rings suggests that we would find some evidence of the effect of this breakdown. Second, the fact that we find evidence of water ice in the rings suggests that there was water ice on Amundsen when it started to break-up. We think the impact which precipitated that break-up was relatively recent, only tens of millions of years.”

The program director from Alpha-1 nodded. “Not enough time for the ice on Amundsen’s surface to completely break down. I see.”

Another big problem with the accretion model, the selenographer clarified, is that it was highly unlikely a moon so relatively large and massive to the planet it orbited could accrete in so close an orbit. If it did, we would expect each body to share a mutual barycentre; that is, to rotate around a common point external to each body, like the dwarf planets Pluto and Charon. Amundsen was very large, relative to Fram, and orbited very closely, relative to their radii. The accretion model simply didn’t account for these facts.

“But Charon did not accrete around Pluto,” the director protested.

The selenographer winced. “A poorly chosen example. But we have only two star systems to draw upon for examples.”

The most likely model, perhaps unimaginatively, was the same which accounted for the formation of Earth’s moon: the giant impact theory. A large object had smashed into Fram in the distant past, spewing material into orbit. The remnants of this object accreted together with the displaced material from Fram, coalescing into Amundsen. Such an impact could explain the angular momentum of Fram and Amundsen; that they did not share a mutual barycentre, and that Fram should continue to rotate so quickly. In the absence of such an impact, Fram might well have become gravitationally locked to Amundsen. This had happened to Pluto and Charon: both dwarf planets kept the same face to each other.

There was other evidence supporting the impact model. Fram’s crust was highly anorthositic, and basalt sheets a common feature of the fractured bedrock; this suggested a catastrophic period of global magmatic activity, of a scale far out of proportion to Fram’s size and geological inactivity. It was likely that Amundsen had also once had a magma ocean; that evidence would only be found by a mission to the moon.

“Of course, if this model is proven, then Amundsen is a particularly unlucky celestial body,” the selenographer said.

Because it had been struck again, catastrophically, tens of millions of years ago. The most recent impact had been the one that shattered Amundsen’s crust, and probably accounted for the lack of water ice. It had been a traumatic experience for Amundsen – Fram’s ring demonstrated that – and while it had not led to the creation of another magma ocean, the impact would have melted away exposed water ice, then lost to space.

“But how did it get the ice, between the impact that formed it and the impact that destroyed it?”

The selenographer explained the benefits of having a moon so massive and close to Fram. It acted, in a local way, like Jupiter acted to the Solar System – is spun along its orbit and scooped up other nearby bodies, effectively protecting the inner system. In the billions of years between major events, Amundsen had been bombarded by asteroids and comets, the latter of which had deposited water and volatile ices on Amundsen’s surface. These deposits were built up laboriously over a period of some four billion years; what the suns stole through ultraviolet sublimation had been replenished by further impacts. Until the latest, most dramatic impact.

The selenographer explained that the break-up of Amundsen was probably not entirely a result of the impact; rather, that whatever hit the moon had fractured its crust and then pushed the moon beyond its Roche limit.

The farthest of the moons from Fram was Nansen. Like Sverdrup, Nansen was a small shepherd moon, regulating the ring which surrounded Fram. Nansen orbited at the far edge of the ring, defining its outer edge. At first we thought both Sverdrup and Nansen were larger pieces of Amundsen, but spectroscopic studies suggested otherwise. Both were captured asteroids, probably carbonaceous chondrites, caught up in the interacting gravities of Fram and Amundsen.

The selenographer pointed out Nansen to the team from Alpha-1. It was a small lump, highlighted by the suns, a grey potato tinted terracotta by the colour of the fuzzy ring. Nansen was the larger of the captured asteroids, just under fifty kilometres on its longest side. Both Nansen and Sverdrup were much larger than the chunks which made up the ring, and were easily distinguished from the surface.

“Far down the line,” the selenographer continued, “we want to capture a third body and use it to stabilise the inner ring, like Nansen stabilises the outer edge. Because Wilbur is far too small.”

But there would be problems. The three moons were already in a precise Laplace resonance: for every one orbit that Sverdrup completed, Amundsen completed two, and Nansen four. Moreover, any shepherd moon placed underneath the ring would be at risk of being pulled apart by the tidal forces of Fram. One solution to this would be to shape an orbit below the synchronous orbit radius. Such a fast orbit, faster than Fram’s own rotation, would stave off the risk of tidal deceleration – for a few million years, at least.

“And there are any number of asteroids out there,” the program director waved an arm in the microgravity out beyond the Fram system, “from which to choose.”

“Indeed. The moons first, however.”





Divergence, Part One

7 11 2007

Over five billion years ago, our neighbourhood within the Universe, on the inner rim of the Orion Arm, was filled with a diffuse mist of hydrogen. This hydrogen formed an immense molecular cloud, and light took dozens of our years to cross this cloud. It was a brilliant, beautiful, resplendent stellar nursery – intertwined vespers of gas were lit by the energetic emissions of nearby, second-generation stars, and highlighted by the glare of the nascent Galactic core.

Today we look into the skies and see such giant molecular clouds in the Orion, Carina and Eagle Nebulas.

The molecular cloud which composed our area of the Galaxy was spun by its orbit and by its density into structures: clumps, bubbles, sheets, and filaments of gas orbited with the Galactic disc. The density of the cloud and its low temperature allowed these structures to agglomerate. Slowly, on timescales incomprehensible to the mind of the intelligence which would eventually arise here, these irregularities condensed and the clumps grew. After less than ten million years, gravitational forces began to exceed the pressure pushing outward from the clumps.

We can think of several causes for the molecular cloud to collapse: the cloud could have hit another, equally-dense broth of hydrogen; or, it could have, in its orbit of the Galaxy, passed through a dense region of the spiral arms, crowded by brilliant young stars already blazing into the night. We know, instead, that one of these nearby stars exploded, and that the uneven force of such a shockwave was the catalyst for collapse. We know this because of the presence of heavy elements in the star systems humanity has visited, and studied – gold, uranium, iron, nickel, lithium, and, crucially, carbon; almost everything heavier than hydrogen and helium, the soup of the Big Bang.

It was probably a massive second-generation star, and its death would have been violent and brief. Heavy elements elements could only have been formed inside the nuclear reaction at the heart of this star, or through neutron absorption; in either case, these elements were scattered by the supernova which marked its death. The high-speed impact of this shocked matter into the molecular cloud caused it to lose stability, and it collapsed.

As it collapsed, it fragmented. Chunks of that filament, clumping together into irregular balls, began to separate and disperse. We now call this turbulent fragmentation. The non-uniform velocities within the molecular cloud compressed the gas in shocks as the whole cloud collapsed, forming objects of varying sizes and densities. As these collapsing clumps of matter distinguished themselves from one another, some became gravitationally unstable, and fragmented again, into two or, in the case of Alpha Centauri, three major parts.

From this fragmentation came the material which would compose Sol and its attendant stellar system, the cradle of mankind, and the matter which would form the Alpha Centauri system.

Although these protostars could not yet create nuclear reactions, they did become warmer and thus began to glow brighter. By collapsing and contracting, they converted gravitational energy into kinetic energy – the closer their constituent atoms fell toward the centre of contraction, the less their gravitational energy, which increased those atoms’ thermal kinetic energy. These clumps warmed; as the hydrogen molecules contracted and collided they became excited and emitted radiation in the microwave and infrared spectrums. Much of this burgeoning radiation escaped, in the beginning, but as the contraction continued the molecular density increased, which began to trap these emissions, and a runaway heating effect began.

The protostars grew hot, quickly, and began to glow a dull, cherry red.

Over a hundred million years, the protostars began to spin, flattening the material which surrounded them into a fat circumstellar disc. This material continued to accrete, and would eventually, in billions of years, become the companions to these stars as they orbited the Galaxy – planets, moons, asteroids, and comets. Then, as young stars, Alpha A and B poured out a strong stellar wind. This pushed back the gases of the disc, and matter stopped falling into the star itself.

Parts of the disc began to clump together as had the molecular cloud: no longer falling toward the protostar, the gravitational heating slowed and the disc cooled, and grains of silicates and ice condensed. The grains of metals, water, ammonia, and methane – that 2% of the mass of the disk planted by the detonation which began its collapse – stuck together electrostatically, and as these clumps ploughed through the disc, they slowly grew into planetesimals. Bound together by a static force and a growing, weak gravity, they swam through the hydrogen and helium gases, and distorted the homogeneity of the disc as they orbited the protostars.

In what we would eventually call the Alpha Centauri system, the interactions of the protostars and their circumstellar discs must have been complicated, as are the orbits of the bodies in the system today. The clumping of the disc around each protostar was influenced by the gravity of the other, causing radial lines to spread from each protostar toward their mutual barycentre. These interactions prohibited the formation of the massive Jovian gas giants which grace the Solar system. The beginnings of these gas giants were pulled apart by the competing gravities of the two stars, or were dissipated by their combined stellar winds, leaving only heavy, silicate planets like Fram to form.

Perhaps their discs merged at their edges, and material was swapped between the protostars and the lumps slowly building in their orbit. It is even possible that Alpha A and B were much closer, these billions of years ago, and swam like titans through a shared circumstellar disc, churning the glowing material about in complex tides.

Alpha A and B were spectacular sights, five billion years ago when they were T Tauri protostars. Their surface temperatures would have been similar to what they are now, though they would have been noticeably brighter, as their radii were smaller. Their discs would have glowed red-hot, and would have neatly bisected the stars themselves. From a distance, above or below the plane of the ecliptic, a dome sat at the centre of the disc – a hemisphere that was half a star, surrounded by a wall of slowly spinning matter. The light of the star would throw million kilometre shadows across the matter that was already clumping together in the disc, and ring systems would have developed in that disc as the interactions of the other star perturbed its orbit.

Across the sky, nearby stars were hot and young, filling space with violent stellar winds.

And then, probably within a million years of one another, and over two hundred million years before Sol, each of the twin stars of Alpha Centauri blazed to Main Sequence life.

Deuterium fusion ignition began, pouring out light, heat and radiation. This outflow slowed the collapse, and was channelled by the discs into bipolar streams. This flow imparted the angular momentum of the star to the material of the disc, just as the magnetic fields of their T Tauri stages had – forever, the planets which formed from the protoplanetary discs would orbit their parent stars on an equal plane of the ecliptic, at the equator of that star, and would match the star’s rotation.

Eventually the heat and mass of these stars would be enough to switch from fusing hydrogen to deuterium to fusing into helium instead. Very quickly, nuclear fusion found a balance where the energy exerted from the core balanced the weight of the collapsing matter which composed the star, and gravitational collapse ceased.

Alpha A accreted more mass than Sol, while Alpha B slightly less; Proxima, orbiting far from the barycentre, accreted about an eighth the mass of Sol. The lump of the molecular cloud from which Proxima developed was small, unstable; nuclear fusion in its heart was slow, fusing hydrogen into helium with much less efficiency than the furnaces at the hearts of Sol, Alpha A or Alpha B. It could not easily radiate photons from its core, an instead moved energy to its surface through convection.

Proxima was dim and isolated – it lacked its own circumstellar disc – and from the heart of the growing Alpha Centauri system, it was an insignificant, flaring bead, tracing an arc around the system thirteen thousand times as far away as Earth is from Sol.

Over a billion years, the clumps of silicates, metals, water, ammonia and methane began to build in size. Initially, they were carried by the turbulent motion of the gas disk itself, like debris carried by the swirling, seething motion of a whirlpool stirred by the two stars. When they collided with one another, they clung together, and grew. Soon they grew so large that they developed their own, shallow gravity wells, and attracted one another without the use of the currents foaming about them. Others formed by coalescing in the mid-plane of the disc, where the heavier material collected through the angular momentum of the disc’s rotation, and collapsed not unlike the molecular cloud had thousands of millions of years before.

Protoplanets kilometres across formed in these ways, and glided in languid orbits. And so began a period of intense violence: these planetesimals collided, smashed together, blasted one another apart, coalesced, and, eventually, formed a stellar system recognisable to us today. Close to the Alpha A and B, volatiles like water and methane could not form, and instead bodies of silicates and metals settled into orbits – we now call the largest of these Fram, Belgica and Maud. Both of these planets were created through countless impacts, which imparted mass to their subjects, and altered their orbits. Belgica and Maud found a comfortable orbits close to Alpha A; Fram, its satellites and rings, was hammered, pushed and pulled into a eccentric orbit around Alpha B.

Stellar winds forced the gaseous hydrogen and helium of the disc far from the stars, and icy volatiles which could not form close to the heat and energy of Alpha A and B found stability here also. Thus formed a massive Oort Cloud – trillions of inert lumps of dirty ice, slung from the warm heart of the system by their hyperbolic orbits, or coalesced from the cooled gas, gathered dozens of times further from the barycentre as was Proxima. The Oort Cloud of Alpha Centauri was of much greater mass and density than Sol’s, for here could be found that material of the circumstellar disc which had formed the cores of Jupiter and Saturn, and the entirety of Uranus, Neptune, and the Kuiper Belt around Sol. These objects, while the best source of water for light years, were also the greatest challenge for the Quoqasi to navigate as we decelerated from our interstellar slingshot, and arrived in Alpha Centauri…