The rogue planet from chapter „Redirection“ was originally planned as a more important location that would actually be visited and the scene of an encounter. This never happened and the place just made an appearance of being mentioned once.
Sargardan is a dwarf planet wandering the galaxy alone, after having been flung out of its solar system aeons earlier. It is a small world, about the size of Earth’s moon but less dense, resulting in a surface gravity about 10% that of Earth.
Its surface still shows traces of atmosphere and vegetation here and there, frozen witnesses of a time long ago, approximately a hundred million years in the past. Because despite its size, Sargardan once held a thin atmosphere and was orbiting its star in the Goldilocks zone - the distance that allows liquid water to exist on the surface and other preconditions for life.
The planet was part of a star system of eleven planets, four rocky inner worlds, six gas giants further away, and one rocky world at the edge of the system.
In these days, at the bottom of its small ocean, organic elements brought in from asteroids collected until they had reached a critical mass. The thin atmosphere and low gravity of Sargardan allowed many of them to reach the ocean waters without burning up or breaking apart, and somehow life got started on this remarkable little planet.
For a few million years, single-cell primitive organisms drifted through the deep waters, with some of them occasionally being lifted upwards, by chance or the warm water of undersea thermal vents rising. Eventually, some of these primitive life forms discovered sunlight and how to use it, and evolution began in earnest, quickly leading to primitive plant life. Algae and corals began the move towards land-based life, and another several million years later, the rocky surface of the planet began to be dotted by colorful plants.
The thin atmosphere of Sargardan did not support spores as a means of reproduction well, so most of those early plants were single organisms growing and expanding, much like mushrooms on Earth, with an underground network of roots. Some plants on Sargardan chose this way, while yet others expanded on the surface, forming webs of plant strands and creeping vines.
In those early days, the surface was rock. It took millions of years of plants growing, dying and decomposing thanks to early bacteria that had joined the plants on their voyage up on the land area of the planet. A voyage well worth it, as Sargardan in those days was only 20% water and most of the surface was land.
On most planets, the thin atmosphere and relatively low amount of surface water would lead to a much weaker water cycle, but the early plant life on Sargardan made its own environment. The planet had high average temperatures, with a typical day ranging from 25°C to 60°C depending on latitude. This high temperature made evaporation an easy method to increase transpiration (water transport from the roots to the leaves) and thus increased nutrient uptake. With more and more of the surface being covered in plant life, the water cycle of Sargardan began to accelerate, cooling down the surface through rainfall and cloud cover. More rainfall caused rivers and lakes to form on the higher elevations, allowing plants to expand to these formerly unsuitable habitats as well.
Meanwhile, in the ocean (Sargardan had only one large ocean), life had taken an evolutionary route towards more complexity. First animals began to appear - jellyfish, trilobites and other forms unknown on Earth. Swarming the ocean and reproducing, these creatures added their own to the mixture that was developing on the planet. Creating biomass from minerals, sunlight and plants consumed as food, a formidable motor of biology had been set in motion.
Life had now expanded towards all corners of the planet, and with more life something else had appeared - competition. Resources were no longer abundant, and some were outright scarce. The first predators appeared, and the first parasitic plants. Millions of years of fights for life, resources, access to water and sunlight and the important hydrothermal vents bringing fresh minerals up from inside the planet brought new forms of life.
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Flight was one of the most challenging evolutionary steps. Despite the lower gravity compared to Earth, the low density of the atmosphere provided major challenges. Especially to the early, small animals like Sargardan’ equivalent of insects, which rely heavily on the density of air to achieve flight. In fact, at the scales of small insects, air is almost a liquid. The Reynolds number is small for these tiny animals, which means the viscosity of air - a negligible factor for large animals - dominates inertial forces.
Without insects escaping into the air, larger animals for which flight was also a more difficult evolutionary achievement but not quite as hard as for the small ones, there was less incentive for flight as well.
For these reasons, it was not until competition on the ground became so fierce and trees started to emerge - providing higher launching points - that the first animals developed gliding abilities as a means to escape predators that had followed them up the tree. From there, primitive flight began to slowly emerge.
But the advantages vs. cost ratio was never as beneficial as it was on more earth-like planets, so free flight, in the sense of starting on the ground and lifting up entirely under one’s own power, never emerged. Flight remained a rarely traveled branch of the evolutionary tree.
Instead, most animals on Sargardan developed thick shells or hide as means of defense. For a few million years, turtle-like animals became the dominant life force, to the point that most predators died out.
In an interesting twist of evolution, Sargardan became maybe the most peaceful planet in the galaxy. Only in the ocean carnivores survived in large numbers, as too thick shells impacted swimming ability too much to be a survival feature.
On land, meanwhile, a new dynamic appeared. With predators out of the picture, the new race was between herbivores and plants. Increasingly, the ever growing number of herbivores threatened to extinguish entire plant populations, causing a food shortage and catastrophic decline of their own populations. Wild swings in populations occurred all over the planet, while the plants struggled to come up with their own defense mechanisms.
Poison was what emerged as the dominant solution. Within a the short timespan of half a million years, Sargardan had changed from a peaceful planet to a poisonous hell. Not only were leaves and roots of most plants filled with deadly poisons, groups of plants had discovered that releasing toxins into the air would keep those eating them away, so they would drive them off before they even chewed off a leave first.
Needless to say, the animals began to develop poison resistances, and an arms race of chemical warfare was in full swing.
Arms races never have winners, only first and second losers. In the case of Sargardan it was the animals. The new and unusual chemical compounds created by the plants lead to changes in biology, and over time entirely new species of animals appeared. Animals armed with poisons of their own, and with acid able to eat through the shells and hides of their victims. At first, these were parasites, but as they grew larger and bolder, predators had made a come-back to the surface of the planet.
But all of this would come to an end when the ultimate low-probability event happened, something so unlikely that even in an entire galaxy, during the entire life time of the universe, it happens only a few times: The star system of Sargardan collided with another star. Or rather: Came so close to it, that the orbits of the planets were changed forever, one of the migrated to the other star, two fell into the sun, and one, Sargardan, was flung out of its solar system, to wander without a sun for all eternity.
A violent event on a cosmic scale, and yet on the scale of living beings, the entire thing happened over thousands of years. Gradually, the orbit shifted. The climate changed. Periods of heat and periods of cold. And then, for several hundred years, Sargardan’s sun became smaller and smaller and smaller, until it became just one of the stars in the eternal night sky.
As the planet moved away from its sun, temperatures dropped lower and lower. At first, life adapted, growing thicker fur and becoming less sensitive to cold. But as snow became a constant factor and then the ocean started to freeze, and then the air itself, life disappeared from Sargardan. For a while, extremophiles held on. But eventually, even they could not survive any longer in the icy void of deep space.
Sargardan wandered the galaxy, dead and lonely. A rock in the void.