Air Burst

7 04 2012

A high-pressure system had formed far to the north of the Colonies. Air warmed at the equator, upon which the Colonies straddled, had risen and drifted away toward the poles; short of twenty degrees north latitude, this mass of air descended to the surface and created a cool, slowly-moving ridge. That ridge pushed down toward the equator, weakening as it moved.

It was thus a clear, cold day as Mierhof and I stepped from the crawler and out onto Fram’s surface.

We were four hours’ north of the Colonies, just over two hundred kilometres from the Yom Kippur mining site. Here there was a clear plain, hundreds of kilometres wide, between two ranges of mountains formed by the uplifted ejecta of massive, ancient craters. The regolith was shallow and, with the bedrock, we made good speed on this relatively flat terrain.

There was a light wind stirring the regolith, and, due to Coriolis force, it came from the northeast. Mierhof swore.

“God damn it’s cold,” he said, tensing up against the wind and holding his body heat jealously. “Reminds me of winter back Home.”

The average atmospheric temperature had dropped as we moved away from perihelion. I tapped at my tablet with the stylus.

“Nine degrees,” I replied.

We both wore knit caps to cover our heads, the most exposed parts of our bodies. Mierhof wrapped a thick scarf around his neck; I enjoyed the bracing cold on my skin. I took a deep breath and pulled away my facemask. I exhaled slowly, watching the steam roll away from my mouth. My breath looked strange, stunted, suppressed as it was by the thick atmosphere. I smiled, and quickly replaced my mask.

“It’s not a Goldilocks world,” I said to Mierhof, “but we could have done a lot worse.”

To the west, the plain rose in a long but gentle incline, and the horizon was far above us. The parallel tracks of our crawler diminished into a point at the crest of that incline. The constancy of that incline belied the violence of its formation: we stood in the basin of a astoundingly large impact crater, so large and so old that it was almost unrecognisable to human eyes. This basin was almost a thousand kilometres across, a depression in Fram’s surface that had been weathered by three billion years of anabatic winds and pockmarked by thousands of younger craters. The force of the impact had punched the surrounding crust upwards, forming extensive highlands that planed away to the far hemisphere.

Mierhof and I unpacked the ground-penetrating radar system from the flatbed of the crawler. Mierhof was remarking at how long it had been since we had used the survey system. We cleared an area of regolith with snow shovels, creating a flat space to deploy the rig.

“You get on that side and get that plate locked down,” he said.

With a thumpthumpthump I hadn’t missed at all, we drilled a borehole and then inserted the GPR antenna into the shaft. I attached my tablet to the rig and brought up the radargram. The terrain at the edge of the basin was heterogeneous, composed of brecciated, smashed bedrock suspended in regolith. With the GPR we might penetrate fifty meters below the surface, far less than had we been working on basalt bedrock.

With Mierhof and I holding each side of the rig for stability, the A44 began to thump out subterranean radar pulses of ultra-high frequency microwave and radio energy. Immediately, reflections reached the rig’s sensors, creating a blurry radargram on my tablet that was clarified with each pulse.

“God damn,” Mierhof said. “They might have been right.”

“Fram!” I replied. “Let me see!”

There were a series of colours, moving like infrared from the warm surface down through yellows and greens to a deep blue. But those colours between red and blue were arranged in parallel bars, and from those bars I could see what was buried beneath me as though staring up at a cross-section of the strata.

There were half a dozen elliptical shapes, like the bow wakes of ships moving up the screen, that showed the presence of large bolides of basalt, and these shapes were suspended on strata lines at various depths. But most interesting was the bottom half of the image. The various stratigraphic layers of regolith and spalled bedrock, written in yellow and green, trailed away into featureless blue; beneath this area of ultrafine regolith there was a second section, an area of high reflectivity, a strata of green highlighted yellow and arrayed in a smooth, flat strata.

“Huh,” I managed.

“Clathrates,” Mierhof replied.

“Looks like it.”

Forty meters beneath my feet, it seemed, in the basin of this impact crater, was a layer of methane ice, a clathrate compound of methane trapped within a lattice of ice. This was a deep sedimentary structure, buried beneath a billion years of regolith. And this layer was thick: from this preliminary GPR pulse, possibly tens of meters thick.

We had found methane ices pooled in the basins of craters near the Colonies, but these had been thin sheets, preserved by the regolith that covered them, ices so thin that once exposed to the thick and warm atmosphere of Fram, sublimated away like magical vespers. But calculations had suggested that, assuming similar ices to be found in craters across Fram, the total amount of water ice was much higher than we had ever expected from the hydrogen and oxygen in the atmosphere.

The theory went that methane produced by the methanogens was trapped within water ices deposited by cometary impacts, and that, in the deep winter of aphelion, water and methane snowed from the skies. This snow was buried by the movement of regolith and, preserved in the depths of craters by the cold of that surface regolith, large reservoirs of methane clathrates might form in the oldest and deepest basins.

Aquifers of vital water and methane might exist across Fram’s surface, undetected and in unimaginable quantities. And so we looked to the largest and most ancient craters for proof.

“Imagine it,” Mierhof said. “All that water, there all the time, waiting to be mined.”

I smiled.

“Think of the energy! We could burn the ice for power and heat. Natural gas. God. Water – and a warmer world.”

That was when it happened.

I had just told Mierhof to get the equipment for a core sample when, from the corner of my eye, I saw a streak of blue-white light, arcing downwards toward the horizon in the north-east. As I turned, I saw that streak begin to fragment into pieces, and as I stared at that cone of smaller arcs of light, I immediately knew what I was looking at.

“Christ, get down!”

I jumped at Mierhof, and with both hands on his shoulders I pulled him to the ground. There was a flash of light. I closed my eyes and buried my face in the regolith, but still I could see the light, and the back of my neck grew hot.

After a moment, Mierhof stirred.

“’The Fram was that?”

We both got to our knees. I wiped away dust from my faceplate. Suspended on the horizon was a dirty column of brown and black, a thick stem of fire and dust balanced on an expanding cloud at its base. Separated from that firestorm were a series of geysers, high plumes of regolith shot up into the sky by dispersed impacts.

“Air burst,” I said at length.

“God damn,” Mierhof replied, rubbing one hand through his beard. “Look at all those impacts. Broke up in the air and shot all those fragments down like a shotgun.”

“What do you think, five or six kilotons?”

Mierhof laughed. “More like ten! My God, look at it.”

The base cloud continued to expand, driven by a pressure shock in the atmosphere. It engulfed the geysers of suspended material that surrounded the airburst cloud. That airburst cloud rose upwards as the heated column of air rose, drawing in cooler air around it; the rolling updraft slowly formed a sinister mushroom cloud. But the wind from the high-pressure front pushed the cloud south-east, and it began to disperse even as it was still rising, raining regolith and vapourised comet across the basin.

Then the sound wave rolled over us, a massive clap that trailed away into a low roar punctuated by the a series of crisp bangs that might have been the impact of the fractured pieces. With that roar came a ground tremor to announce the violent creation of Fram’s youngest crater.

“Here’s a scary thought,” I ventured. “That comet must have travelled billions and billions of kilometres. Imagine if it had fallen just twenty kilometres short.”

Mierhof looked at me with eyes that held little patience for cynicism.

“Here’s a nicer thought: imagine that much force hitting a clathrate deposit. All that methane and water vapour quickly dumped into the atmosphere. We might warm Fram in decades, not centuries…”

We watched the cloud disperse for half an hour before we began to drill the bore for the core sample.




One response

24 08 2012
Epilogue « Orbital Shipyards: Alpha Centauri System

[…] after the first Foundation Day, we discovered evidence of methane ice aquifers. The basic human need for water drove prospecting for purer sources of water ice, and technical […]

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