A, G, U and X

19 02 2012

Ngan said to Lindenmeyr: “Let me show you what we’ve learned so far.”

He moved away from the trough of methanogens and retrieved a tablet from his workbench. The tablet awoke from hibernation, and, in the reflection on Ngan’s faceplate, Lindenmeyr saw a series of brightly coloured images, rotating in imitation of three dimensions.

“If you’ll indulge me,” Ngan began, “I might ask you a question. How do you imagine alien life? How do you imagine something entirely new?”

Lindenmeyr paused for a moment.

“Is this a philosophical question?”

“Oh yes,” Ngan replied. “Imagine, if you will, a new colour. A colour no one has even seen before. Or imagine a taste you’ve never tasted. Anything you imagine in your mind is based on what you know, what you’ve experienced, what is familiar.”

“Of course.”

“We can’t possibly imagine something entirely new and different. And if we saw it, we likely wouldn’t recognise it.”

Lindenmeyr cleared her throat. “Like Stanislaw Lem.”

“Exactly.” Ngan returned to the trough of methanogens with the tablet. “The likelihood that any kind of life that evolved away from Earth would be recognisable to us, much less look like humans with pointy ears, is infinitesimal.”

“And yet we recognise these methanogens.”

“Oh yes. And here we return to that philosophical question.”

Ngan explained that the basic building blocks of life as humans had experienced it were readily and widely available in the Universe. Organic compounds such as hydrocarbons and amino acids were found in comets along with methanol, formaldehyde, ethanol and ethane, even hydrogen cyanide. The emergence of life was not some religious miracle, but rather a simple matter of chemistry – the interaction of methane, water, ammonia, hydrogen and the creation of amino acids, the building blocks of proteins.

Astonishingly, more complex nucleobases could also be formed on meteorites, asteroids and comets. Together with amino acids, these nucleobases could under the right conditions evolve into complex proteins, nucleotides, DNA.

Ngan showed a series of slides to Lindenmeyr who, although not an expert in organic chemistry, recognised the association of molecules of hydrogen, nitrogen, carbon and oxygen into an amino acid.

“So we took it back to the beginning,” Ngan said. “Because the end product is so different, we go back to the building blocks that the methanogens must have started with.”

“Ah. Now I see the point of your question. Here is the experience we use to recognise the alien.”

Ngan nodded.

“To continue with the ‘building blocks’ analogy, we figured that all life starts with the same materials and then goes about building different shapes, forms, assemblies.”

He flipped to another slide that showed a complex structure of tangled lines branching from a single curved strand. Where the tangles were clustered they grew away from the thicker strand, and bunched together like fruit on the limb of a tree.

“What is it?” Lindenmeyr asked.

Ngan chuckled. “Oh, this is the only macromolecule that composes the methanogens.”

Ngan continued and grew more animated as he explained. When tested, the methanogens had not demonstrated chirality because they were composed of neither proteins nor DNA. But here, rotating in false colours, was their analogy for both.

“It is somewhat similar to RNA,” Ngan said. “Essential for all life on Earth. In fact, viruses use RNA for genetic material. But it’s not RNA. We don’t know what to call it. We liken it to RNA only because we need that anchor of familiarity. It is only similar to RNA in so far as both are single-stranded molecules with shorter chains of nucleobases, that in turn produce some quite complex three-dimensional structures.”

Lindenmeyr turned from the spinning macromolecule on the tablet screen to the methanogens arrayed in a line between her and Ngan.

“Wow,” she managed.

“Oh yes,” Ngan replied. “At the moment, we’re half-jokingly calling it FNA.”

“FNA?”

Ngan grinned. “Framnucleic acid.”

And, arrayed around that single-strand backbone, were many of the building blocks seeded throughout the Universe: the primary nucleobases of adenine, guanine, the A, and G from DNA-based life, along with uracil, the U found in RNA; and the modified purine bases xanthine and hypoxanthine. Of these four nucleobases, FNA clustered into groups of two, rather than the groups of three into which DNA clustered.

“Actually,” Ngan said, “the simplicity of FNA is more akin to very, very early precursors to DNA than RNA as we know it. Say, four billion years ago. The precursor used only two nucleobases and a handful of amino acids, and worked well long before life evolved the triplet code it uses now. These doublets seem to work well for such a simple lifeform.”

Conspicuously absent from the image of the FNA macromolecule were thymine and cytosine, two of the nucleobases of DNA. Lindenmeyr asked Ngan why C and T were missing from FNA.

“We have a theory about that,” he explained. “Thymine and cytosine bonds are most susceptible to damage from ultraviolet light; in fact, most skin cancers from exposure to ultraviolet are a result of a thymine dimer, where ultraviolet photons damage the bonds between nucleobases and distort the macromolecule. Because of the direct exposure to ultraviolet light, we think the methanogens have evolved without thymine and cytosine.”

“A clever adaptation to the environment,” Lindenmeyr ventured, “but it cripples their genetic complexity.”

“Oh yes. Unfortunately, the methanogens won’t teach us a new way to deal with ultraviolet light; they’ve simply evolved away that part of them damaged by UV.”

Ngan brushed through the next slides. The absence of proteins dramatically simplified the process of replication, he explained. The FNA in the methanogens did not appear to articulate with a Fram version of ribosomes, and so did not communicate instructions to assemble amino acids into proteins through protein biosynthesis.

But it was so much easier to describe what life on Fram didn’t do, rather than what it did do. This difficulty was related, Ngan said, to his earlier comments about conceptualising ideas through the familiar.

Nonetheless, early work suggested that the FNA contained some amount of genetic information, but rather than communicating that information to assemble cells, the FNA duplicated itself in a manner similar to a virus; it did so, however, without a host cell. This duplication was in part related to the complex structures that the single-strand backbone of FNA allowed. The form of that structure was repeated in each duplication – limiting the opportunity to evolve, but allowing for very durable structures once natural selection identified a viable arrangement of nucleobases.

“These methanogens don’t so much ‘grow’ as they ‘self-copy,’” Ngan concluded. “We still don’t know how FNA forms these fronds, in the absence of both proteins and cells.”

Lindenmeyr turned over the fronds in her hands.

“Is it life?”

Ngan paused. “Yes and no. They are subject to natural selection, as evidenced by the absence of thymine. They possess analogues of genes. But they grow through self-assembly, rather than cell division.”

“Life,” Lindenmeyr said again. “Wow, I don’t even know how to communicate what I’m trying to say. I mean, we’re life, you and I, and we evolved from amino acids and nucleobases, and we go out into the Universe and we find these methanogens, and we stand here in this room and…and life asks if life is life.”

Ngan chuckled.

“Oh yes. I think of it like this: spread around the Universe are kits containing all the parts to make something. But there are no sets of instructions, no recipes, in these kits; not even someone or something to assemble the parts.”

Lindenmeyr nodded. “That’s the magic, I think. As best they can…the kits assemble themselves.”

Ngan spread his hands.

“And here we are.”





Empire of the Setting Suns

8 02 2012

Like spray whipped from a wave, grains of regolith blew from the crest of the dune that stretched away to either side of Sze Leng and Ruslan. These shifting, shimmering sheets of dust were held aloft by the thick atmosphere and carried away by the wind, a force patiently shaping and rearranging the surface of Fram.

They sat in the lee of the dune, slightly beneath the crest. Sze Leng sat in front of Ruslan and her slender body was huddled up against him. Stretching away before them was a rippled surface, a sea of regolith wrinkled into dunes and gathered in parallel curves by katabatic winds. This was Fram’s softer landscape: kilometres of deep regolith uninterrupted by outcroppings of fractured bedrock or by the spalling of craters, although both underlay this basin, Ruslan knew, tens of meters below the surface.

Ruslan adjusted his faceplate by rubbing his chin against the top of Sze Leng’s head.

“Well worth the hike,” Sze Leng said.

Her voice was quiet, and Ruslan tapped the volume on his mike.

“We first noticed it in an areomagnetic survey,” Ruslan explained. “You can’t tell from the regolith, but this entire basin is pockmarked with craters that show up on the magnetometer. We think they’re quite ancient, based on the layering of regolith. The deeper layers have lithified into eolianite .”

“Oh.”

Alpha Centauri B was almost below the horizon. Its orange-yellow light illuminated the sky above its disc in a stunning stratum of incandescent orange through a fiery spectrum to vermillion. The ocean of dunes stretched off to the horizon. The setting suns lit the crests as darkness gathered in the troughs between dunes, creating alternating bands of gold and deep purple. Fram’s ring bisected the sunset, and cast an almost translucent shadow across the sky and landscape – offset from Alpha B by Fram’s marginal axial tilt.

Separated from Alpha B by an apparent distance of perhaps half the diameter of its disc was Alpha Centauri A, an intensely bright point a thousand times brighter than the full moon from Earth, but which could be entirely blocked out by a thumb held outstretched. Although higher in the sky than Alpha B, Alpha A was following B below the horizon.

“Tell me there’s nothing to mine out here,” Sze Leng said. “It would be such a shame.”

She turned her head over her right shoulder to face him and Ruslan sensed that she was grinning, but the gesture was lost in the glaring reflection of the sunsets in her faceplate.

“The underlying bedrock showed concentrations of magnetite and iron oxide. That’s how we detected the craters. But they’re not rich concentrations.”

Sze Leng’s head rolled lazily back into that comfortable space where Ruslan’s neck met his shoulder at the collarbone, and she stared upwards. The stars had begun to populate the darkening sky with glimmers of white, red and blue, flickering in the shifting atmosphere. Her eyes immediately sought familiarity: the trinity of stars that composed Orion’s Belt, and the brightening sparks of Rigel and Betelgeuse, a formation of lights unchanged by the distance from Home.

“Sometimes, when I’m out surveying,” Ruslan whispered, “I try to think of what will be here in a hundred, five hundred, a thousand years. We’re just starting out. Imagine a city that stretches from the Colonies out here to the Periphery, a great city, like those we left behind on Earth. Maybe someone will live here, eat here, sleep here, right where we are sitting, and will watch the suns set like us.”

Sze Leng smiled.

“Maybe.” she replied, dreamily. “Maybe, when we’ve warmed Fram and thinned the atmosphere, this plain will be a forest, filled with tall, spindly trees, creating soil and turning carbon dioxide into oxygen. And lovers will walk through the gardens, maybe even without suits, dreaming of some place called Earth.”

Sze Leng turned around so that she was facing Ruslan, and, without the tall reflection of the sunsets in her faceplate, Ruslan could see the look of wonder on her face.

Alpha B slipped beneath the dusty horizon, and the twilight deepened. Ruslan imagined Fram spinning, and the terminator line between light and dark crawling over its face. The sky above him grew blue-black, chasing the plum, vermillion and deep red toward the horizon. Amundsen was behind them, close to setting in the east; lit by both stars, it glowed brighter as the day dwindled away, turning the blackness around it into the colour of faded rubber.

The intoxicating majesty of the sunsets diminished, and Ruslan’s thoughts became darker.

“Maybe nations will rise and fall and fight over these dusty plains.”

Caught between day and night, framed by the light of both moon and star, Sze Leng stirred and asked,

“Should we head back?”





Ultraviolet

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…