8 02 2012

The effect of the gravities of two stars upon Fram’s orbit was quite pronounced.

Fram’s orbit was highly eccentric, meaning that it was a not a simple circle around Alpha B, but rather an elongated ellipse. Traced simply, Alpha B sat inside one end – called an apsis – of that ellipse, while the other apsis stretched away toward Alpha A. But neither Alpha A nor B were stationary, and themselves orbited a mutual barycentre. Their own orbit greatly complicated Fram’s orbit. The apsides changed with each orbit relative to the position of both stars. This was called apsidal precession. Each time Fram completed an orbit of Alpha B, Alpha A had moved relative to its binary partner, and its gravity tugged at Fram. As a result, each completed ellipse reorientated itself toward Alpha A.

Astronomers explained apsidal precession by tracing a complex spiral that represented Fram’s orbit. The lines of that spiral converged at periapsis – the apsis that coincided with perihelion, Fram’s closest approach to Alpha B – but diverged in wandering arcs near aphelion, as each orbit traced a different apoapsis. Fram was moving away from periapsis and, slowly, methodically, irrevocably, gliding toward apoapsis. Fram had only in the last week passed periapsis, and took roughly three Earth years to complete an orbit, meaning that the apoapsis of that orbit was about eighteen months away.

There were many concerns about the habitability of Fram, almost all of which had been foreseen and discussed long before the Quoqasi left Sol. Only one among these was its wandering orbit, which itself posed the major problem of exposure to ultraviolet light.

Alpha B was less of a concern than Alpha A. Alpha A was larger, hotter and brighter than Sol, while Alpha B was similarly smaller and cooler. We knew that hot objects preferentially emitted radiation at shorter wavelengths and higher frequencies. Wien’s displacement law described the relationship between temperature and peak frequency. The hotter the object, in this case a star, the shorter the wavelength at which it emitted radiation. This was why hot, A-type stars like Sirius tended to emit blue light in the visible spectrum, while cooler M-type stars like Proxima tended toward red light.

But visible light was only one component of the electromagnetic spectrum. Higher up the spectrum according to frequency were ultraviolet, x-rays and gamma rays. Hotter stars not only pumped out more light, but also preferentially emitted these higher frequency, shorter wavelength types of electromagnetic radiation.

Not only did Alpha A pump out more energy than both Sol and Alpha B, but it also preferred to emit more dangerous energy.

Humans had evolved while sheltered from most ultraviolet radiation by Earth’s ozone layer, a belt of the stratosphere where the interaction of molecular oxygen and solar ultraviolet light continuously interconverted oxygen from O2 to O3; the process also converted ultraviolet radiation into thermal energy. But Fram, of course, possessed no ozone layer. Almost all of the oxygen in Fram’s atmosphere was covalently bonded with a carbon atom to form carbon dioxide, which was not only poisonous to breath but offered no shelter from ultraviolet light.

From Earth, it was easy to miss some of the features of Fram that would challenge our early efforts, such as the damage that the regolith would pose to our vehicles and equipment. But it was comparatively simpler to understand the stellar system, and we were prepared for the worst of the ultraviolet light. Equipment at risk of UV degradation, like synthetic polymers, had been reinforced with stabilisers and absorbers – such as benzophenones, zinc oxide, and titanium dioxide. Moreover, the same lack of independent oxygen in the atmosphere that prevented the development of an ozone layer also suppressed the reaction between ultraviolet rays and free radicals that led to the worst of polymer degradation.

All of these measures would be tested at apoapsis, when Fram was suspended between the two stars and at its closest approach to the more threatening Alpha A. At that point there would be no real night, but rather a bright twilight, the sky dark blue and the terrain of the planet lit with a quality of light like the totality of a solar eclipse on Earth. Exposure to ultraviolet would be highest at apoapsis.

Some of the biologists noted the similarity of the colonisation of Fram to the emergence of life on Earth. Early prokaryotes approached the surface of Earth’s oceans billions of years ago, before Earth had developed an ozone layer, and, exposed to the worst UV light, promptly died out. Those that survived had developed the necessary enzymes, base excision repair enzymes, which identified and corrected the genetic damage caused by exposure to ultraviolet.

And so, as Fram continued gracefully along its complex orbit, we began to study how the methanogens had evolved to tolerate such intense ultraviolet light…


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…

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…


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.”

Proton Storm

12 02 2010

On the penultimate day of the +150 Conference, the magnetic field of Alpha B became in one place knotted, and then snapped back on itself – releasing a tremendous solar flare.

Ground-based observatories watched as an enormous prominence, aglow with plasma heated to tens of millions of kelvin, arced over the surface of Alpha B. Astronomers observed the tremendous forces of the star; the magnetic field of the photosphere had twisted and penetrated to the corona, allowing the corona to suddenly and violently release magnetic energy outward. In addition to photons and plasma, the flare vented electrons, protons, ions and gamma rays, and accelerated these to a significant proportion of the speed of light.

Port Mayflower was well inside Fram’s magnetic field, and most of the orbiters were currently docked to Wilbur. One orbiter, however – the Harry Gold – had been in a high orbit of Fram, just outside the outer edge of the ring system, when the solar flare erupted. The orbiter had been mapping the break-up of Amundsen and identifying new bodies which might disrupt the now-stable ring, or impact Fram itself.

There were a series of quick exchanges between the Harry Gold, capcom, and the observatories; these were almost useless, as the flare had been a particularly concentrated ejection, and the orbiter lacked the delta-vee to quickly slip inside the shadow of Fram or around the far side of Amundsen.

Thirty minutes after the first observation, the proton storm hit. Soft x-rays washed over the atmosphere, cutting communications with the Harry Gold. Auroras danced in the skies above the Colonies, lit green and pink at the edges. Then the hard stuff hit, a cascade of hard x-rays and gamma radiation slipping through the orbiter and its crew as if they weren’t even there.

Capcom re-established contact with Harry Gold an hour later. The six crew were still alive, but barely – dosimeters showed that they had taken a massive 850-900 rems of radiation. They were told that another orbiter would not reach them for a day; some said their goodbyes to comrades and loved ones over the choppy radio.

The tragic irony was that scientific study of Alpha A and B had not been included in the list of topics for the +150 Conference. Those who championed such a study had been told that only applied science was being seriously considered by the Conference. Purely scientific work could wait until the Colony was well-established and prospering, and until that point, only science with a practical value would be undertaken.

The study of the three stars in the solar system had become a very practical notion, if exploration of the solar system were to continue, and an expedition to the Kuiper Belt be launched…

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…

Rigel Kentaurus

13 05 2007

Our new home was a world named Fram. It orbited the dimmest of the close binary Alpha Centauri A and Alpha Centauri B. It was one of three planets we had found in the system. Maud and Belgica were small balls of iron that orbited close to Alpha Centauri A, while Fram orbited Alpha Centauri B alone.

Fram was a small world, no larger than Saturn’s moon Titan; Fram possessed a similarly thick atmosphere, although less exotic. An atmosphere of mostly carbon dioxide (65%) and hydrogen (15%), with lesser and trace gases (methane 8%, argon 7%, nitrogen 5%) enshrouded the planet.

The two stars orbited a mutual barycentre, and took just under eighty years to complete orbits of one another. Alpha A and Alpha B at their closest were 11.4 AUs apart, still farther than the distance from Sol to Saturn. At their farthest, they were 36 AUs apart, greater than the orbit of Neptune.

Fram was in a highly elliptical orbit of Alpha Centauri B, which at its perihelion was 0.75 AU from Alpha B; its orbit stretched away toward Alpha Centauri A with an aphelion of 1.3 AU. This looping orbit wobbled with each revolution, as its aphelion was tugged toward Alpha A by the competing gravities of the binary and the rotation of Alpha A around the barycentre. Fram completed an orbit of Alpha Centauri B every three years and five Earth months.

Even at its closest point to Alpha B, less than the distance between Earth and Sol, Fram only skirted the outer edge of Alpha B’s habitable zone. Fram was thus a cold world. When it grazed the HZ around perihelion, Fram’s surface temperature hovered between 5 and 15 degrees Celsius. At aphelion, methane would bond with water ices and would snow from the sky and settle into the craters that pockmarked Fram’s surface; thin sheets of methane and water ice were thus frozen beneath the regolith at the basins of many craters.

Alpha Centauri B was a dim main sequence, orange red dwarf, about eighty-six to ninety percent Sol’s diameter and mass, but only forty-two to fifty-two percent its luminosity. Because of Fram’s elliptical orbit, which was at its closest to the bright Alpha Centauri A when at aphelion to Alpha Centauri B, the planet was at its coldest when the two stars were at their brightest. From Fram, Alpha A appeared to brighten as the two stars approached and dimmed as they receded. Under our e-suits we would wear thermals and coats and scarves.

Much of the matter that, given the stable conditions of Sol, might had agglomerated into large planets had instead been scattered and distributed by the competing gravities of the binary stars; in the Alpha Centauri system there had formed no Jovians, no gas giants, no large terrestrial planets. The entire system was composed of comets and asteroids and lumps of planetesimals too small to form into spherical shapes under their own gravity, all churned about in complex orbits. Fram was the largest of these rich, metallic lumps; it had three satellites that we named Nansen, Sverdrup and Amundsen.

Fram had an extensive ring system, despite being a much smaller world than the magnificent, ringed giants of distant Sol. Its largest moon, Amundsen had been disintegrating for about six million years: struck directly by a planetesimal likely flung by Proxima, Amundsen had shattered and now swam through a complex ring system formed from the debris. It was likely that all of Fram’s ring system had, once, been a part of Amundsen. This ring would, as with the formation of the Moon around Earth, clear in a few billion years, as the deformed remains of Amundsen and the small shepherd moons Nansen and Sverdrup consumed the debris.

But not all of Amundsen had settled so easily into a new orbit. There were strings of fresh craters across the scarred face of Fram, and impact sites across the leading hemispheres of Nansen and Sverdrup. Alarmingly, in the twenty-five years since the first automated probes from Sol had shot through the system at relativistic speeds, a new and massive impact site had formed on Fram’s northern hemisphere.

Fram’s surface had been weathered as had Earth’s Moon by regular impacts for billions of years. But unlike the Moon, Fram had an atmosphere, through which small meteors quickly burned up, and wind and weather fronts and dust storms, which moved the dusty regolith around and disguised all but those enormous craters that had geologically altered the landscape.

Nonetheless, there had been no peak period of bombardment for any of the planets of the system, as there had been in distant Sol; rather, bombardment was a geologically regular occurrence. Impacts from comets had given Fram what little water ice there was on its surface and the lesser gases in its atmosphere.

Fram was a forbidding place. It was cold and dry and its atmosphere poisonous, and yet, a form of life was found here. In the deepest basins of craters and in rilles between uplifted basalt sheets there existed a kind of translucent vegetation – anaerobic methanogens, which sought out the volatile ices frozen here and converted these to methane. It was to these methanogens that Fram owed the methane in its atmosphere.

There was a certain desolate beauty to Fram. At perihelion, Alpha A would disappear for months at a time behind Alpha B, while at aphelion both stars would be opposite one another, and would banish night entirely. Proxima, a flare star, could dramatically brighten and in moments appear as bright as Jupiter from Earth. All three of Fram’s moons could go into eclipse simultaneously, a sight bisected by Fram’s elegant ring. The zodiacal light was bright and intense, even long past sunsets; aurorae filled the night sky, sometimes from two directions, varying in colour; the planet’s ring cast a band of light close to the horizon and divided the hemispheres; and asteroids looped about solar system, brighter than artificial satellites in low-orbit.

From Alpha Centauri, Sol was a bright yellow speck, maybe the magnitude of Capella seen from Earth, far away in the constellation Cassiopeia; and it transformed that constellation’s w shape into a less precise zig-zag…