by Neil Clarke
It was as if the rolligon had dropped over a curb, but there was no curb. I was in the driving chair; Mike was asleep in the hammock. I told the AI to stop, and looked out through the canopy at the 180-degree panorama. The horizon was drawn closely all around. An ancient crater eroded by three billion years of micrometeorite bombardment dished it to the north and a few pockmarked boulders were sprinkled here and there, including a fractured block as big as a house. Something skittered in the corner of my eye—a little rock rolling down the gentle five degree slope we were climbing, plowing a meandering track in the dust. It ran out quite a way. The rolligon swayed gently, from side to side. I found I was gripping the padded arms of the chair so tightly my knuckles had turned white. Behind me, Mike stirred in the hammock and sleepily asked what was up; at the same moment, I saw the gas plume.
It was very faint, visible only because the dust it lofted caught the sunlight. Gas plumes were not uncommon on the Moon, caused by pockets of radon and other products of fission decay of unstable isotopes overpressuring the crevices where they collected. Earth-based astronomers sometimes glimpsed them when they temporarily obscured surface features while dissipating into vacuum. This, though, was different, more like a heat-driven geyser, venting steadily from a source below the horizon.
I told the AI to drive toward it. Mike leaned beside me, scratching himself through his suit of thermal underwear. He smelled strongly of old sweat;
we hadn’t bathed properly since the interlude with the Swedes. I had a sudden insight and said, “How hot is the black hole?”
“Oh, the smaller the black hole, the more fiercely it radiates. It’s a simple inverse relationship. It was pretty hot to begin with, but it’s been getting cooler as it accretes mass. Hmm.”
“Is it still hot enough to melt rock?”
Mike’s eyes refocused. “You know, I think it must have been much bigger than I first thought. Anyway, anything that gets close enough to it to melt is already falling toward the event horizon. That’s why there was no trace of melting or burning when it dropped out of the reaction chamber. But there’s also the heat generated by friction as stuff pours toward its gravity well.”
“Then it’s remelting the interior. Those anomalies in the seismology signals are melt caverns full of lava.”
Mike said thoughtfully, “I’m sure we’ll start picking up a weak magnetic field soon, when the iron core liquifies and starts circulating. Of course, the end will be pretty close by then. Wow. That thing out there is really big.”
The rolligon was climbing a long gentle slope toward the top of a curved ridge more than a kilometer high, the remnants of the rim of a crater which had been mostly buried by the fluid lava flow which had formed the Oceanus Procellarum. I told the AI to stop when I spotted the source of the plume. It was a huge fresh-looking crevice that ran out from a volcanic dome; gas was jetting out of the slumped side of the dome like steam from a boiling kettle. Dust fell straight down in sheets kilometers long. Already, an appreciable ray of brighter material was forming on the regolith beneath the plume.
“We should get closer,” Mike said. He was rocking back and forth in his chair like a delighted child.
“I don’t think so. There will be plenty of rocks lofted along with the gas and dust.”
We transmitted some pictures, then suited up and went outside to set up a seismology package. The sun was in the east, painting long shadows on the ground, which shook, ever so gently, under my boots. With no atmosphere to scatter the light, shadows were razor sharp, and color changed as I moved about. The dusty regolith was deep brown in my shadow, but a bright blinding white when I looked toward the sun, turning ashy gray to either side. The gas plume glittered and flashed against the black sky. I told Mike that it was probably from a source deep in the megaregolith; pressure increased in gas pockets with depth. A quake, probably at the interface between the megaregolith and the rigid crust, must have opened a path to the surface.
“There’ll be a lot more of these,” Mike said.
“It’ll blow itself out soon enough.”
But it was still venting strongly when we had finished our work, and we drove a long way north to skirt around it, with Mike scratching away on his slate, factoring this new evidence into his calculations.
We were out for another two weeks, ending our run in lunar night at the Big Array Station at Korolev. It was one of the biggest craters on the far side, with slumped terraced walls and hummocky rim deposits like ranges of low hills. Its floor was spattered with newer craters, including a dark-floored lava-flooded crater on its southern edge which was now the focus of a series of quakes of steadily increasing amplitude. Korolev Station, up on the rim, was being evacuated; the radio telescopes of the Big Array, scattered across the far side in a regular pattern, were to be kept running by remote link. Most of the personnel had already departed by shuttle, and although there were still large amounts of equipment to be taken out, the railway which linked Korolev with Clavius had been cut by a rock slide. After a couple of spooky days’ rest in the almost deserted yet fully functional station, Mike and I went out with a couple of other GLPs to supervise the robots which were clearing the slide and re-laying track.
It was a nice ride: the pressurized railcar had a big observational bubble, and I spent a lot of time up there, watching the heavily cratered highland plains flow past at two hundred kilometers an hour. The Orientale Basin dominated the west side of the Moon: a fissured basin of fractured blocks partly flooded with impact melt lava and ringed round with three immense scarps and an inner bench like ripples frozen in rock. The engineers had cut the railway through the rings of the Rook and Cordillera Mountains; the landslide had blocked the track where it passed close to one of the tall knobs of the Montes Rook Formation, a ten-kilometer-high piece of ejecta which had smashed down onto the surrounding plain—the impact really was very big.
A slide had run out from one of its steeply graded faces, covering more than a kilometer of track, and we were more than a week out there, helping the robots fix everything up. When we finally arrived at the station in Clavius, it was a day ahead of the Mendeleev eruption and the beginning of the evacuation of the Moon.
The whole floor of the Mendeleev Crater had fractured into blocks in the biggest quake ever recorded on the Moon, and lava had flooded up through dykes emplaced between the blocks. Lava vented from dykes beyond the crater rim, too, and flowed a long way, forming a new mare. Other vents appeared, setting off secondary quakes and long rock slides. The Moon shivered and shook uneasily, as if awakening from a long sleep.
Small teams were sent out to collect the old Rangers, Lunas, Surveyors, Lunokhods, and descent stages of Apollo LEMs from the first wave of Moon exploration. Mike and I went out for a last time, to Mare Tranquillitatis, to the site of the first manned lunar landing.
When a permanent scientific presence had first been established on the Moon, there was considerable debate about what to do with the sites of the Apollo landings and the various old robot probes and other debris scattered across the surface. There had been a serious proposal to dome the Apollo 11 site to protect it from damage by micrometeorites and to stop people from swiping souvenirs, but even without protection it would last for millions of years, and everyone on the Moon was tagged with a continuously monitored global positioning sensor so no one could go anywhere without it being logged, and in the end the site had been left open.
We arrived a few hours after dawn. It was a lonely place, not much visited despite its historic importance. A big squat carrier rocket had gone ahead, landing two kilometers to the north, and the robots were already waiting. There were four of us: a historian from the Museum of Air and Space in Washington, a photographer, and Mike and me. The site was ringed around with laser sensors. As we loped through the perimeter, an automatic beacon on the common band warned us that we were trespassing on a U.N. heritage site and started to recite the relevant penalties until the historian found it and turned it off. The angular
platform of the lunar module’s descent stage had been scorched by the rocket of the ascent stage; the gold foil which had wrapped it was torn and tattered, white paint beneath turned tan by exposure to the sun’s raw ultraviolet. One of its spidery legs had collapsed after a recent quake focused near new volcanic cones to the southeast. We lifted everything, working inward toward the ascent stage: the Passive Seismometer and the Laser Ranging Retroreflector; the flag, its ordinary fabric, stiffened by wires, faded and fragile; an assortment of discarded geology tools; human waste and food containers and wipes and other litter in crumbling jettison bags; the plaque with a message from a longdead president. Before the descent stage was lifted away, a robot sawed away a chunk of dirt beside its ladder, the spot where the first human footprint had been made on the Moon. There was some dispute about which print was actually the first, so two square meters were carefully lifted. And at last the descent stage was carried off to the cargo rocket, and there was only a litter of cleated footprints left, our own overlaying Armstrong’s and Aldrin’s.
It was time to go.
As the eruptions grew more frequent, even the skeleton crews of the various stations were evacuated, leaving a host of robot surveyors in close orbit or crawling about the troubled surface to monitor the unfolding disaster. Mike and I went on one of the last shuttles, everyone crowding to the ports as it made a single low orbital pass before lighting out for Earth.
It was six months after the Mendeleev X-1 incident. The heat generated by the black hole’s accretion process and tidal forces had remelted the iron core; pockets of molten basalt in the mantle had swollen and conjoined. A vast rift opened in the Oceanus Procellarum, splitting the nearside down its northwestern quadrant and raising new scarps as high and jagged as those in an old Chesley Bonestell painting. The Orientale Basin flooded with lava and the fractured blocks of the Maunder formation sank like foundering ships as new lava flows began to well up. Volcanic activity was less on the far side, where the crust was thicker, but the Mare Ingenii collapsed and reflooded, forming a vast new basin which swallowed the Jules Verne and Gagarin Craters.
It took two more months.
As the end neared, the Moon’s surface split into short-lived plates afloat on a wholly molten mantle, with lava-filled rifts opening and scabbing over and reopening along their edges. There were frantic attempts to insure that the population of the Earth’s southern hemisphere would all have some kind of shelter, for the Moon would be in the sky above the Pacific in its final hour. Those unlucky or stubborn enough to remain outside saw the Moon rise for the last time, half-full, the dark part of her disk riven with glowing cracks which spread as the black hole sucked in exponentially increasing amounts of matter. And then there was a terrific flare of light, brighter than a thousand suns. Those witnesses who had not been blinded saw that the Moon was gone, leaving expanding shells of luminous gas around a fading image trapped at the edge of the black hole’s event horizon, and a short-lived accretion disk as ejected material spiraled back into the black hole, which, although it massed the same as the Moon it had devoured, had an event horizon circumference of less than a millimeter.
The radiation pulse was mostly absorbed by the Earth’s atmosphere; the orbit of the space station had been altered so that it was in opposition when the Moon vanished. I was aboard it at the time, and spent the next six months helping repair satellites whose circuits had been fried.
There are still tides, of course, for the same amount of mass still orbits the Earth. Marine organisms which synchronized their reproduction by the Moon’s phases, such as horseshoe crabs, corals, and palolo worms, were in danger of extinction, but a cooperative mission by NASA and the Russian and European space agencies lofted a space mirror which reflects the same amount of light as the Moon, and even goes through the same phases. There’ll be a big problem in 5 X 1043 years, when by loss of mass through Hawking radiation the black hole finally becomes small enough to begin its runaway evaporation. But long before then the sun will have evolved into a white dwarf and guttered out; even its very protons will have decayed. The black hole will be the last remnant of the solar system in a cooling and vastly expanded universe.
There are various proposals to make use of the black hole—as the ultimate garbage disposal device (I want to be well away from the solar system when they try that), or as an interstellar signaling device, for if it can be made to bob in its orbit (perhaps by putting another black hole in orbit around it), it will produce sharply focused gravity waves of tremendous amplitude. Meanwhile, it will keep the physicists busy for a thousand years. Mike is working at one of the stations which orbit beyond its event horizon. I keep in touch with him by E-mail, but the correspondence is becoming more and more infrequent as he vanishes into his own personal event horizon.
As for me, I’m heading out. The space program has realigned its goals, and it turns out that the black hole retained the Moon’s rotational energy, so it provides a useful slingshot for free acceleration. After all, there are plenty of other moons in the solar system, and most are far more interesting than the one we lost.
For Stephen Baxter
1999
Stephen Baxter (www.stephen-baxter.com) is one of the most important science fiction writers to emerge from Britain in the past thirty years. He’s the author of more than fifty books and over a hundred short stories. His most recent novels are Xeelee: Vengeance and Xeelee: Redemption. “People Came from Earth” is part of his Manifold sequence and Stephen will be returning to that multiverse with his in-progress series, World Engines.
PEOPLE CAME FROM EARTH
Stephen Baxter
At Dawn I stepped out of my house. The air frosted white from my nose, and the deep Moon chill cut through papery flesh to my spindly bones. The silvergray light came from Earth and Mirror in the sky: twin spheres, the one milky cloud, the other a hard image of the sun. But the sun itself was already shouldering above the horizon. Beads of light like trapped stars marked rim mountain summits, and a deep bloody crimson was working its way high into our tall sky. I imagined I could see the lid of that sky, the millennial leaking of our air into space.
I walked down the path that leads to the circular sea. There was frost everywhere, of course, but the path’s lunar dirt, patiently raked in my youth, is friendly and gripped my sandals. The water at the sea’s rim was black and oily, lapping softly. I could see the gray sheen of ice farther out, and the hard glint of pack ice beyond that, though the close horizon hid the bulk of the sea from me. Fingers of sunlight stretched across the ice, and gray-gold smoke shimmered above open water.
I listened to the ice for a while. There is a constant tumult of groans and cracks as the ice rises and falls on the sea’s mighty shoulders. The water never freezes at Tycho’s rim; conversely, it never thaws at the center, so that there is a fat torus of ice floating out there around the central mountains. It is as if the rim of this artificial ocean is striving to emulate the unfrozen seas of Earth which bore its makers, while its remote heart is straining to grow back the cold carapace it enjoyed when our water—and air—still orbited remote Jupiter.
I thought I heard a barking out on the pack ice. Perhaps it was a seal. A bell clanked: an early fishing boat leaving port, a fat, comforting sound that carried through the still dense air. I sought the boat’s lights, but my eyes, rheumy, stinging with cold, failed me.
I paid attention to my creaking body: the aches in my too-thin, too-long, calcium-starved bones, the obscure spurts of pain in my urethral system, the strange itches that afflict my liver-spotted flesh. I was already growing too cold. Mirror returns enough heat to the Moon’s long Night to keep our seas and air from snowing out around us, but I would welcome a little more comfort.
I turned and began to labor back up my regolith path to my house.
And when I got there, Berge, my nephew, was waiting for me. I did not know then, of course, that he would not survive the new Day.
He was eager to talk about Leonardo da V inc
i.
He had taken off his wings and stacked them up against the concrete wall of my house. I could see how the wings were thick with frost, so dense the paper feathers could surely have had little play.
I scolded him even as I brought him into the warmth, and prepared hot soup and tea for him in my pressure kettles. “You’re a fool as your father was,” I said. “I was with him when he fell from the sky, leaving you orphaned. You know how dangerous it is in the pre-Dawn turbulence.”
“Ah, but the power of those great thermals, Uncle,” he said, as he accepted the soup. “I can fly miles high without the slightest effort.”
I would have berated him further, which is the prerogative of old age. But I didn’t have the heart. He stood before me, eager, heartbreakingly thin. Berge always was slender, even compared to the rest of us skinny lunar folk; but now he was clearly frail. Even these long minutes after landing, he was still panting, and his smooth fashionably-shaven scalp (so bare it showed the great bubble profile of his lunar-born skull) was dotted with beads of grimy sweat.
And, most ominous of all, a waxy, golden sheen seemed to linger about his skin. I had no desire to raise that—not here, not now, not until I was sure what it meant, that it wasn’t some trickery of my own age-yellowed eyes.
So I kept my counsel. We made our ritual obeisance—murmurs about dedicating our bones and flesh to the salvation of the world—and finished up our soup.
And then, with his youthful eagerness, Berge launched into the seminar he was evidently itching to deliver on Leonardo da V inci, long-dead citizen of a long-dead planet. Brusquely displacing the empty soup bowls to the floor, he produced papers from his jacket and spread them out before me. The sheets, yellowed and stained with age, were covered in a crabby, indecipherable handwriting, broken with sketches of gadgets or flowing water or geometric figures. I picked out a luminously beautiful sketch of the crescent Earth—
