This is an older version of this story, from 2006. Here's the latest version, from 2022.
A thousand years later, Humanity finally reached that magical point that had been anticipated since the dawn of mass media: the day when it became quicker, cheaper, safer and easier to go to the stars and look at them up close than to squint at them through mind-bogglingly powerful telescopes.
It was then that the Space Age - the REAL Space Age - began in earnest. Having long since built themselves perfect worlds on nearly every rock in the Solar System large enough to moor a habbubble, there remained nothing else in the universe more attractive to Humanity at large than the prospect of finally taking to the stars en masse. So it was that planet after planet orbiting star after star became home to new families of Humans, living under new skies and adapting to new environments, breeding new animals and looking at each other and the worlds around them with ever-new eyes. At last, the Human race was out of the cradle - at last, it no longer had a single point of failure. The future never seemed so expansive, the possibilities never so endless.
It was in the year CE 3198 that the UAAE Jasper Jaeyo set off around the curve of the galactic rim, far beyond the sphere of inhabited space, on a mission to circumnavigate the galactic centre and map every step of the way.
By thirteen years into the mission, the crew of the Jasper Jaeyo had stellar cartography and astrometry refined to a fine art. As the Jaeyo bored its jagged, counterintuitive space-filling fractal route, a 500-strong fleet of smaller, manned craft followed it, connected invisibly to the mothership by fine holeworm threads. Each smaller craft flitted from stellar system to stellar system on the Jaeyo's route, deploying dozens of their own autonomous drones in each system to study its gas giants, terrestrial planets, comets, asteroids and parent star or stars. Meanwhile the manned craft swept onwards, covering more systems in the same way - typically, two or three dozen each in a standard day - continously gathering and collating telemetry, and occasionally capturing small comets to manufacture new drones, or returning to the mothership to exchange crew and undergo maintenance.
This was the routine which gradually came to be abandoned on the discovery of planet 0099-4836/010-D.
The anomalous data was only received a few hours after the subcraft Culver had left the system, and it was another two hours before confirmation arrived from a second drone and the Culver's subcaptain elected to backtrack and check the mysterious grey planet out. The drones' data proved accurate. Here was a planet, not substantially bigger than Sol-Earth, in a very much Sol-Earth-like orbit around a very much Sol-like single star, yet absolutely perfectly smooth - a blank slate, an oblate spheroid with an equatorial radius of 6,988 kilometres and a polar radius of 6,966, smooth to as many decimal places as the Culver's instruments could determine. There was no trace of atmosphere nor of variation in the pale grey colouring of its surface. There were no mountains, no tectonic plates, no plateaus, no geographical features, nothing.
There were no impact craters. At all.
Damodomad, the subcaptain of the Culver, ordered a kinetic probe to be shot into the planet; a spectrographic analysis of the debris propelled into space from the impact point showed the planet to be made mostly of something approaching magnesium steel, with a finely graded mixture of surprisingly complex chemicals mixed in with it.
Further kinetic probes at the planet's pole and equator gave similar readings; seismic readings of the impacts' passage through the planet's interior suggested it consisted of the same substance all the way through, or at least to the depth at which pressure forced it to become liquid.
Domad ordered a drone to land on the planet's surface and retrieve a sample. Contact was lost with the drone immediately after it landed.
The same happened with the second drone, even though it landed much more carefully than the first, using an entirely different method of propulsion which should have seen it land with less force than a feather.
The third drone was specifically configured to deliver extremely high-speed live internal telemetry even as it landed. A short time after it, too, became unresponsive, preliminary analysis of the telemetry revealed that the drone had been consumed by a sort of grey wave - consumed from the landing legs upwards to the radio dish in a matter of milliseconds.
It was exactly one standard day after the planet had been discovered that the UAAE Jasper Jaeyo itself arrived in the 0099-4836/010 system, having altered course to support the Culver. Ten further subcraft had also joined them along with countless extra drones.
The Culver docked with its parent one astronomical unit above the star's north pole.
"So what are we actually looking at here?" asked captain Ekrem Merke of the Jasper Jaeyo. They were on the bridge of the ship, a gigantic three-dimensional panoramic projection of the planet spread out below them, scattered with neon blue crosshairs representing other vessels.
"You may have heard of the Blue-Age Mimas colony disaster from your history lessons," said Domad, taking a sheaf of paper from his assistant and shuffling through the pages. "We're hypothesising that something very similar happened here, only on a vastly larger scale. We believe that at one point this planet had intelligent inhabitants. Their nanotechnology was advanced, more than ours is even now. They, whoever they were, did what the Unknown Miman did - created a primitive nanobot with a very simple set of instructions: while one, propagate."
"Suicide. That's the first lesson in basic nanotechnology. First, program the off switch. Everybody knows that."
"Quite right. It is a VERY simple and obvious mistake to make, which itself casts doubt on the supposition that it was a mistake at all. The circumstances surrounding this event are purely guesswork at this point, but releasing the nanofungus could indeed have been intentional suicide. Accidentally creating a bot which can chew up a life-support computer's innards' worth of doped silicon transistors like the Unknown Miman did is easy. Building a bot capable of swallowing an entire planet is something you simply cannot do by accident unless you have a very high-level programming language and a very pseudointelligent basic spore at your disposal. At that scale, power generation and chemical decomposition become significant enough factors that a simple eternal propagator would not be intelligent enough to handle by itself.
"Anyway. Regardless of how it happened, it's happened. The bot probably swept out the entire planet's surface over the course of months or years. Once everything on the surface was consumed it had nowhere to go - so it obeyed its initial instructions and began to slurp up the planet's atmosphere too, and to eat downwards as far as possible towards its core. The planet became smoothed over because this was the most efficient configuration - then, once it reached the point where nothing more could be consumed, the fungus simply idled, waiting for more consumables to present themselves."
"Which explains the absence of impact craters."
"Exactly, sir. I arranged for a smallish asteroid to be dropped on the planet to see what would happen, we can show you that right now. This is sped up by a factor of thirty..."
A holographic asteroid faded into being some distance above the holographic planet, and fell in towards it under gravity. Merke stood up and went over to squint close at the asteroid as it fell, then at the growing patch of bare grey metal where it was going to hit. Then he stood back to watch the impact.
"The asteroid itself takes several hours to be completely broken down, but the impact crater itself, you'll notice, is flattened much earlier in the timeline. We doped the asteroid with a radioisotope we could track from low orbit and found that the new concentrations of elements brought by interplanetary impacts are distributed evenly around the rest of the planet very rapidly. Which means there could have been a thousand similar impacts and we'd find no evidence of it. This planet could have been sitting here for potentially hundreds of millions of years."
Merke turned from the hologram towards the live display of the fleet's in-system deployment. He took a few steps towards it, taking in the gigantic array of figures attached to each blip.
"Hundreds of millions of years?" he asked, turning around.
"Possibly even billions," said the subcaptain. "We just don't know."
"Millions of years, sitting here, looking for something to eat. Sitting here thinking about finding new things to eat. Waiting for something new to eat to come along... Give me a detailed scan of the surface of this planet. I know we already have one, run it again. Find anomalies."
A young ensign named Beryt soon answered: "Three anomalies, sir. Moderate thruster activity and tentative holeworm drive signatures. Satellite scans show some sort of narrow pinnacles taking shape at the locations where... where each of the probes landed. They... they seem to be... rockets. They're taking shape incredibly quickly..."
"Navigator, plot a course back to Sol. Straight path. No deviations. Do it right now. Engage the moment it's done. Maximum velocity."
Domad protested, "Sir, this must be normal behaviour! The rest of the celestial bodies in this star system are untainted. Think about what that means!"
Beryt cried, "We have ignition at the first landing site! The other two rockets have just disappeared but we're tracking their threads—"
Two red emergency lights lit up on the fleet graphic. Both were in close proximity to the grey planet. Four more in higher orbit lit up a second later, just as the first two faded to empty blue-edged squares, symbolising lost contact. In an eyeblink twenty more were lit. That was the whole complement of in-system ships.
The Jaeyo was already a light-day out of the system and accelerating.
Something slug-like, dark and difficult for the Jaeyo's computer sensors to get a grip on, accelerated out of the blue-lit system behind them, and off at an angle, towards another nearby star. As the image of the system shrank behind them, more black slug-things were detected heading in other directions, targeting other systems. Ships of the greater fleet began to appear at the edges of the display as the field of view widened - red lights were already crawling over their scattered formations.
None of the ships, not even the probes, had weapons.
Obeying the emergency "Follow me" command issued manually by Captain Merke, only a handful of the swiftest subcraft were able to escape the expanding maelstrom of hungry nanotechnology. They fell into a defensive pattern behind the Jaeyo, holding steady in its slipstream as it forged a superluminal path ahead. No signs of pursuit were detected, but could that be held to signify anything? Detecting a ship-sized object which didn't want to be found, even at a distance of mere light-seconds, was all but impossible. All ships and drones of the Jaeyo fleet carried beacons for precisely this reason.
Five days into the race home, the combined engineering forces of the surviving eight vessels succeeded in transplanting the Jaeyo's primary holeworm drive into the chassis of the lightest capable subcraft, the Bluearck. It would take an estimated six months to reach Sol, redlining all the way. Behind them, the sphere of influence of the nanofungus was already two hundred light years wide.
There was hope that Sol could be reached and Humanity at large warned before the first slugs arrived in Human space. But who knew what a million-year-old planet-sized brain could do? Who knew how fast it could build its fastest messengers, now that it knew what space travel was?