2493 Oumuamua was an Alien Artifact

In 2017 an extrasolar comet passed through the Solar system. It moved at such a high speed that it was bound to come from outside the Solar system. Oumuamua, as it was named, was initially regarded as an interstellar asteroid. Later it was re-classified as a comet because small changes in the trajectory indicated outgassing.

The amazing thing about it was its shape. Astronomers of that time could only see a small dot through their telescopes. But the dot was blinking. This led to the conclusion that Oumuamua was rotating fast. From the brightness curve, they calculated that Oumuamua was at least 5 times as long as it was wide shaped like a cigar of about 250 x 50 meters. The fast rotation led to the conclusion that Oumuamua must be a solid body, for only solid bodies can withstand high centrifugal forces. Unfortunately, this theory could not be verified directly, because Oumuamua was much too fast for a rendezvous mission and there was no probe in the vicinity.

Spectroscopy showed a high metal content. Early on, there were suspicions that Oumuamua might be of artificial origin. When it was at its minimum distance of 33 million kilometers radio receivers would have detected transmissions of a tenth of a watt. But there were no active emissions.

Oumuamua quickly disappeared into the depths of space and fell into oblivion. Each year the distance grew by almost a light hour, for centuries.

In 2493 Oumuamua is almost 400 billion kilometers away. That is two light weeks or 2700 AU, 2700 times as far from the sun as the Earth, far out in the Oort cloud.

In 2493 however, experimental FTL drives can master such a distance. An expedition sets out to visit the old comet. Its vector is well known. Direction and speed have been precisely measured in the 21st century. And if the path has not been disturbed in the last 400 odd years, Oumuamua should be within a spatial volume of three cubic AU or 10 trillion trillion cubic kilometers. The difficulty is not to cover the distance to the comet, but to track it down in the target area.

The comet is not easily detectable, at least not visually. Out there, in the Oort cloud, it gets billions of times less light than the Earth and it is also quite dark. However, radar does the job. The research vessel deploys several strong radar transmitters in the target area and then waits for echoes. After repeating this procedure several times, they detect a signal at the edge of their search area. While the travel time over 2700 AU was only eight days, the search has taken 40 days.

The expedition approaches Oumuamua. Finally, they can really see the object. They must illuminate it with spotlights, because it is a dark thing in the blackness of space. The surface is very smooth. It is not cigar shaped, as was once thought. In fact, it is a cylinder. Oumuamua is clearly of artificial origin. It is a perfect cylinder, 300 meters long and 50 meters in diameter. At first glance it looks like an empty fuel tank. A close examination reveals residue water ice inside. This must have been the source of any outgassing supposed centuries ago. The surface has countless impact craters of micrometeorites and dust particles. A statistical analysis of the crater distribution indicates an age of 150 million years. That makes Oumuamua the oldest product of a technical civilization ever discovered.

The object has some minor bulges and mounts, but – apart from the meteorite craters – no obvious damage. It looks as if Oumuamua had been deliberately released and not blasted off by an accident. 150 million years ago it had been part of a larger structure, a space station, a ship, or a habitat. Oumuamua probably had served as a water tank. After the tank had been emptied, it was disconnected. Then it drifted away and has remained on its own trajectory ever since.

Oumuamua is moving away from the Solar system at 26 kilometers per second. However, this is a similar orbit around the galactic center as our sun. The relative speed is small compared to the common speed around the center of the Milky Way at about 225 km/s. For comparison, the Sun itself is 20 km/s faster than the average speed of the stars in its vicinity.

The current relative velocity of Oumuamua with respect to the Solar system does not mean that long ago a technical construction was moving at 26 km/s escape velocity. Perhaps it was almost at rest relative to its home system. Perhaps Oumuamua belonged to the inhabitants of an Oort object there. Since then, both Sol and Oumuamua have been travelling roughly two-thirds of a full circle around the galactic center. Time and again either has changed its direction slightly due to gravitational interactions with other stars. The current relative velocity is the consequence of many subtle vector changes. But they are both basically on a similar orbit around the galaxy.

Ultimately, Oumuamua is an ancient piece of junk that happened to pass through the Solar system by chance. Astronomers in the 21st century could not but take it for a natural object. Anything else would have been considered science fiction or wishful thinking.

In the 21st century, people did not know how widespread technical civilizations actually are, how long they exist, and how gigantic their operations are compared to planetary societies. Modern technical civilizations have an industrial capacity a million times higher than the Earth of the 20th century. In hundreds of millions of years there were millions of such civilizations. Over time, all of them together have left behind many trillions of trillions of objects like Oumuamua. This is an order of magnitude that almost approaches the number of natural stray objects in the galaxy.

It was just a coincidence that the first interstellar visitor ever detected was a technical relic. Many other that later visited the Solar system were of natural origin.

Having completed the mission, the research vessel sets course for Sol to travel back. It brings home another proof, that there are many technical civilizations in the galaxy. Humanity already knows that they are out there, from remote observations and artifacts found in the Solar system.

About a hundred years before this mission set out for Oumuamua, the BISON array detected large structures in a star system, that will later be known as Artu. And since then, many signs of extrasolar civilizations have been detected. Including the so-called Pandora Artifact at Saturn, the KAIO-ship in the asteroid belt, and of course the ages old alien Copernicus moon base.

It's just that the FTL drives are not yet good enough to cover the huge distances between stars. This trip was 8 days, with an experimental drive under full power. It was not only a research mission, but also a test flight for the brand-new, factor-2 FTL drive. Soon enough FTL technology will be reliable enough for sustained operation over months. And within a decade, humans will take on the long and risky journey to other stars. And also: the even greater distances – to other inhabited star systems.