Colony events

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This article is for the PC version of Stellaris only.

These events are all restricted to a certain colony. Only one event per colony is possible and many have multiple options for ending them. There is no right or wrong decision, as every choice can lead to either positive or negative outcomes later.

Subterranean Civilization

As an early game event, it is possible for a colony experiencing seismic disturbances to discover that the planet was already inhabited by a subterranean civilization. Contact can be established for 1000 Society research society, or a preemptive strike can be launched for 5000 Engineering research engineering. If the timer is left to expire an envoy from the subterranean civilization will arrive to establish contact instead.

If contact is established you are given the option to coexist in peace or demand their surrender. Demanding their surrender will cause them to surface and invade a month later. Choosing to coexist instead will grant a society research bonus to the planet. Coexisting with them will eventually bring dilemmas, namely whether to help them in a time of famine, allow refuge to a chaste religious group chased out of the tunnels by a small subterranean army, react to one of their excavations unknowingly causing earthquakes or accept a request to share military technology or refuse. Having good relationships with the civilization may grant you gifts of minerals or allow your xenoanthropologists to live with them for a time, granting society research. Having bad relations will cause them to become hostile and invade.

If they invade and your armies are defeated the planet will be taken over by them and they will form their own Fanatic Militarist.png fanatic militarist and Authoritarian.png authoritarian empire. If they are defeated a special project to destroy the subterranean civilization will be given. Unless the project is started they will periodically invade or send out a raiding party to ruin a building.

A preemptive strike will all but destroy the subterranean civilization. Later possible outcomes are finding a survivor pocket which can be executed or enslaved, finding gold mines or the civilization's treasury, the collapse of a tunnel network creating a tile blocker and claiming their tunnels as your own, spawning 3 tile blockers, which after removing grant 3 rare planetary features, which add +3 maximum mining-, generator- and agriculture districts each to the planet and increase the district limit by 2 each.

Abandoned Terraforming Equipment

As another early game event, it is possible for colony founded on a planet that isn't your ideal to discover that the reason the planet's climate and biosphere are unstable due to an unfinished terraforming project of another empire thousands of years in the past. The planet has the Abandoned Terraforming Project modifier, giving the colony -20% Food.png food and -10% Mod pop happiness.png happiness. Since the aged terraforming complex is still standing you are given the option of either resuming the process or dismantling the equipment.

Finishing the project will remove the modifier and instantly terraform the planet into either a normal world, a gaia world with +20% Mod pop growth req.png Pop Growth speed, a toxic world or a normal world with mutated creatures that have to be defeated. They are strong, usually too strong for the garrison to defeat without additional armies. Defeating them will add a mutant landfill building which produces a large amount of society research, more than any biolab. However, later a creature will evolve into a marauding stalker beast, ambushing hundreds of workers and the security teams sent to investigate and adding a happiness penalty until an added special project to hunt down the creature will be finished. If the special project is left to expire the creature will either die naturally and leave colonists unhappy with your failure or breed and unleash a horde of similar marauding creatures on the colony.

Dismantling the complex will grant a large bonus of society research, and the Terraforming tech if you do not already have it, but leave the climate unstable. Climate instability can result in deadly weather and droughts.

Migrating Forests

Shortly after a colony is founded on a planet with significant vegetation it is possible to discover that almost the entirety of its flora is mobile, regularly migrating to new areas and creating three wandering forests tile blockers that cannot be removed. You are given the option to remove them by either studying them to find a solution for 500 Society research society or burn them for 500 Engineering research engineering. Until a decision is made the wandering forests tile blockers will periodically move to any free space on the planet.

Studying them will create a permanent wandering forests reserve tile blocker that grants +3 Society research adjacency bonus. Possible outcomes include finding that the forests were sentient and adapted to coexist with the colonists and give a happiness bonus, having the biologists coming up with additional research or having the planet get a food production penalty due to a forest fire.

If the forests are burned the tile blockers will be destroyed. Possible outcomes are uncovering a mineral deposit, damaging the ecology of the planet or revealing that the forests were sentient and turn aggressive and invade.

Pollen Aphrodisiac

Shortly after colonizing it, it is possible to discover on one of the wet or frozen planet types that the flora exude large amounts of pollen and start an optional research project that requires a science ship to investigate it further. Researching the project will grant Society research society research points.

Even if the project hasn't been researched one year later you will discover the long term exposure effects on the colonists. The pollen acts as an aphrodisiac and you are given the option to remove it for 400 Energy.png and end the event chain or leave it to grant +10% Mod pop happiness.png happiness. Another year later it is revealed that the aphrodisiac is also making the people less productive, giving the planet -15% Pop job.png job production and starting a special project to study the problem. The project times out in 1080 days, takes 30 days to complete, requires a science ship and a level 3 scientist, and grants 150 Society research society research and a 10% mitigation of the Pop job.png job production penalty. After one more year it will be revealed that the pheromone is also making the colonists less likely to migrate giving them -70% Mod pop migration time.png migration speed. Three months later it will be revealed that the colony officials are becoming more distant and you are given the option to either send someone to investigate and gradually end the event chain or do nothing.

Refusing to do anything will lead to the rise of a cult two years later. Two months later the cult will change into a doomsday cult, something coinciding with a chemical change in the pollen. You are given a special project to avert a disaster. It requires a science ship and a level 4 scientist and finishing it will reveal that the pollen was about to evolve into a neurotoxin and destroy the flower via a planet-wide pesticide bombing run. If the special project is not started in time the pollen will destroy all life on the planet and turn it into a toxic world. The entire empire will get a -10% reduction in Mod pop happiness.png happiness and Unity.png unity for ten years. Two years later the toxic miasma will lift and the planet will reveal to have become a desert world.

Helpful Drones

This event chain can only take place on colonized planets with an uninhabitable moon. An ancient technology will activate on the moon due to the colonization efforts, starting a special project to investigate further. The project requires a science ship and finishing it will reveal that the readings were ancient drones that will randomly go online and offline. Eventually the drones will awaken and descend on the planet surface to remove a tile blocker if any exists. The first time they awaken again they will build a space elevator which, while interesting for study, is inefficient and has to be removed. You will receive 250 Engineering research engineering research but for two years the planet will get a -20% Minerals.png minerals production. The second time they will awaken again the drones will dump a large cache of minerals on the moon, enriching it with minerals that can be mined by a mining station. The third time they awaken again they will unearth an ancient satellite on the moon, giving it a permanent society production that can be gained by building a research station. The fourth time the drones awaken a number of them will self-destruct via orbital reentry. Eventually you will be notified that their remains are analyzed and another notice later will shed some light on the drones.

Sometime later the final event will happen. Examining the drones will reveal that they were sent in advance by an advanced group of pirates to fatten a colony in preparation for their attack, which will occur in two years. You are given the option to either just prepare for the attack, giving you 80 Influence.png influence and facing them when they arrive, set the drones against them and face them weaker but earlier or destroy the drones and grant 350 Engineering research engineering but have the pirates attack with a fleet twice as strong.

The pirate fleet at normal or reduced strength is weak and can be destroyed by a small fleet or a spaceport orbiting the planet. Choosing to destroy the drones however will have them come more prepared.


Shortly after colonizing a number of planets three random pops on one of them will be infected with a new infectious disease. Most ethics have the option to kill or quarantine the infected pops for a cost of 100 Influence.png influence. The other option, available to everyone, is to enact a research station and attempt to cure it.

Killing the infected pops has a 50% chance to end the event and 50% chance to be insufficient, causing three other pops to become infected and once again bringing the option to kill or quarantine them for a 50 Influence.png influence cost or attempt to find a cure. Killing or quarantining the infected a second time will be sufficient but this option is not available if you have insufficient population.

The plague causes -20% Mod pop happiness.png happiness and Mod habitability.png habitability and it will likely infect most population on the planet. With enough time it is lethal. However, as long as a pop is working on the plague research station tile a cure will eventually be researched, curing everyone (it is likely that the plague station only cure population on it. Is is advised to move infected people anytime one is cured). The reward for curing it is 125 Influence.png influence as well as Unity.png unity and Society research society research and a Plague Memorial building on the planet which adds a permanent 5% Mod pop happiness.png happiness and 2 unity, as long as the memorial is being worked. Resettle plagued pop will cause it to be stuck with the penalty forever, althought it will neither die nor spread the plague.

Progress on the cure is not made if the plague research station tile is not worked on. Without a cure the population will be eradicated by the plague, and the plague will die with them.

Curiously enough, players playing as a machine empire can also have this event happen to them: plague can infect both machines and robots.


An empire holding a negative attitude towards you might send an assassin after a planetary governor and kill the said leader. The assassin is apprehended as it makes its escape and you are left to decide its fate. You can either keep the assassin as an information source to receive 125 Influence.png influence or execute it for a cost of 50 Influence.png influence to give -25% Mod country edict influence cost.png edict cost, +25% Mod army morale.png army morale and -20% Mod pop happiness.png happiness to the planet for a year. Militarist.png militarist and Fanatic Militarist.png fanatic militarist empires do not get a happiness reduction. Pacifist.png pacifist and Fanatic Pacifist.png fanatic pacifist will get the option to sent the assassin home as a show of good faith instead, granting a temporary boost in Diplomacy opinion.png opinion.

Odd Factory

Another early game event, it is possible to uncover a hidden factory on a colony. The building adds an "Odd Factory" worker job that's produces 4 Alloys.png alloy. If the factory is staffed it is possible a few months afterwards for the pop to suddenly vanish. The second time it happens it will be revealed that the factory is booby-trapped and will promptly be secured. It is also possible for the factory to explode and become ruined, giving you the option to recover either the energy or the mineral production. Or nothing might happen at all at the factory. A common tactic is when the Factory is discovered, you can immediately demolish it. This will give you the same option as if it exploded or was ruined, giving the tile another 3 energy or minerals. After you select what you want, place either a power plant or mine respectively, making it a very lucrative tile in the late game.

Submerged Cruiser

A mid game event, it is possible for a colony on a wet world to find an alien cruiser submerged under the polar ocean and get the option to either issue a special project to salvage it or to scrap it and reverse engineer cruiser technology if you haven't researched it already. Salvaging it will grant a permanent +10% Evasion evasion for all ships and either the alien cruiser if it can be restored or 500 Minerals.png minerals if it can't. However it is also possible for the special project to fail and the ship to explode and create some planetary devastation.

Asteroid Sighted

It is possible for a colony's deep space tracking arrays to discover an asteroid on a collision course with the colony. The asteroid is durable but can slowly be destroyed with a fleet. Occasionally your allies will send a fleet to destroy it if you don't. Destroying the asteroid will allow the colony to salvage it, granting 1000 Minerals.png minerals. If the asteroid impacts the planet it will kill multiple pops and leave behind a crater tile blocker.

Lost to Bureaucracy

A repeatable event possible on well established planets, it is possible for clerical errors to bring unfortunate living conditions upon the populace. You are given the option to either do nothing, which will result in two tile blockers, or invest Influence.png influence and Energy.png energy in the area and receive Unity.png unity for your efforts. The investment cost is halved for Authoritarian.png authoritarian and Fanatic Authoritarian.png fanatic authoritarian. More aggressive government types can also throw out the inhabitants and raze the area, ruining two buildings and enraging some pops but gaining Influence.png influence.

A New Species

Shortly after Tech gene tailoring.png Gene Tailoring is researched if there is a colonized planet with a Mod habitability.png habitability lower than 40% and at least 4 primary species pops with under 50% happiness, some of its population will genetically modify themselves to the planet's environment. Their traits will also be changed to a new random set and the planet they adapted to will be considered their homeworld. It should be noted that they can gain Tomb World habitability this way.

If the original species, and by extension the modified one, are not Pacifist or Xenophile then not long after the alteration occurs tensions between the genetically modified and unmodified species will rise. Both species on the planet will become Xenophobe.png Xenophobe if not already.

Shortly afterwards the conflict will escalate. Both modified and unmodified species will randomly carry out attacks against each other, killing a random pop on the planet each time. As a result, the genetically modified population will further alter themselves to gain the upper hand with the Strong.png strong and Rapid Breeders.png rapid breeders traits. Eventually the conflict will end without further notice. There is no reward except for the newly created species, which may or may not be desired.

Due to their collective unity hive mind empires cannot get this event.

Planet Modifier Events

These colony events will occur shortly after colonizing a planet with the said modifier.

Titanic Life Event

Shortly after colonizing a world with titanic life you will get a notification about your researchers proposing to study it. You are given the option of either giving them green light and add the Titanic Life Study special project that costs 1000 Society research society research, or refuse their requests. Xenophile.png xenophile and Fanatic Xenophile.png fanatic xenophile empires can opt for a monitoring special project instead, costing 1500 Society research society research but having less chances of a bad outcome, while Xenophobe.png xenophobe and Fanatic Xenophobe.png fanatic xenophobe empires can opt for a necropsies study instead, costing only 500 Society research society research but having more chances of a bad outcome. Finally, Auth hive mind.png hive mind empires can choose to harvest the titans, resulting in an especially low chance of a good outcome but adding a permanent +100% Food.png food modifier to the planet. The outcomes are either a peaceful coexistence and the ability to recruit 3 powerful titanic beast armies at a time from the planet or enraging the titans and having them attempt to fully occupy the planet.

Irradiated World Event

Shortly after colonizing an irradiated world you might get a notification about the colonists wanting to find out what happened to the world before they came. In a month the investigation will conclude that the planet's previous population was destroyed either by orbital bombardment from another race and study the impact sites (permanent Physics Research physics bonus), an interstellar invasion and study battlefield remains (permanent Engineering research engineering bonus) or a nuclear war (permanent Society research society bonus). It is also possible for the investigation to reveal nothing and grant +10% Physics ResearchEngineering researchSociety research research bonus and -15% Mod pop happiness.png.

Atmospheric Hallucinogen Event

As long as there is a planet with the atmospheric hallucinogen modifier, you might get a request to remove it. You can either agree and do a special project to remove it for 500 Engineering research engineering or leave it as it is. Removing it can also result in a breakthrough where the air is filtered to only remove the negative effects of the hallucinogen.

Repeatable Events

Unlike all the other events these ones are repeatable. They cannot happen more than once per year however.

  • Asteroid Impacts Event Planets with the asteroid impacts modifier can suffer an impact that will give a -5% Mod pop happiness.png happiness penalty for a year and occasionally ruin a building. Each time it happens you are given the option to issue an Asteroid Defense System special project or just claim that the colonists knew the risks. The special project costs 500 Engineering research engineering and will protect the planet from further impacts.
  • Unstable Tectonics Event Planets with unstable tectonics can suffer earthquakes due to tectonic shifts that will give a -5% Mod pop happiness.png happiness penalty for a year and either uncover a batch of minerals or open a sinkhole tile blocker.
  • Strong Magnetic Field Event A planet with a strong magnetic field will sometimes experience for a year either a +20% Physics ResearchEngineering researchSociety research research bonus or a -10% Physics ResearchEngineering researchSociety research research and -5% Mod pop happiness.png happiness penalty.
  • Asteroid Belt Event A comet might pass through the asteroid belt of a colony with the said modifier, leaving a spectacular sight for the population and giving them +10% Mod pop happiness.png happiness for a year. Alternatively, if your empire is Fanatic Xenophobe.png fanatic xenophobe it will add a -10% Mod pop happiness.png happiness modifier, claiming that the comet is an omen of the dangers space represents.

Tomb World Events

These colony events can only take place on tomb worlds.

Pacifist Movement

As a tomb world colony develops, it is possible for the colonists to gain a strong attraction towards pacifism, believing that they have obligation to speak out against the violence that destroyed the tomb world's previous inhabitants.

Orbital Debris

Some tomb worlds feature a very high amount of orbital debris from satellites and missile launch platforms that were destroyed by anti-satellite weapons during the war. Once a colony develops enough to be interfered by it the Orbital Debris modifier will be added, giving the colony a +10% Mod planet building cost mult.png building cost penalty due to the ship navigational hazard. A very short and free special project to remove the debris field will be added. Rarely, removing the orbital debris will salvage it for 500 Minerals.png minerals as well. Not removing it will eventually lead to the orbital reentry of some of the debris, killing a pop, and the crash of a freighter on the planet, leaving a crater tile blocker.

Underground Vault

One possible discovery on a tomb world is a sealed fallout shelter. A special project can be started, requiring 5000 Engineering research engineering to open the vault. The vault can contain skeletal remains and research logs, a horde of mutants or a large population of survivors which can be integrated, enslaved or sealed back and have the entrance buried if your empire is Xenophobe.png xenophobe or Fanatic Xenophobe.png fanatic xenophobe.

Nuclear Bomb

Another possible discovery on a tomb world is an undetonated hydrogen bomb. The colonists inadvertently activate the timer, starting a special project that needs 200 Engineering research engineering to disarm it. If the timer is left to expire the bomb will explode on a populated tile, turning everything into a bomb crater.

Pre-FTL Relics

Relics that can be found on a tomb world shortly after colonizing it are a particle accelerator that generates +6 Physics Research physics research, surviving infrastructure granting a -10% Mod planet building cost mult.png building cost or a derelict space station granting a one time bonus of Engineering research engineering research.


This class G star system contains a rich Tomb world and a frozen planet with rich Society research deposit. Some time after colonization there will be a necessity to start a special project in extremely short time (180 Time days)

  • Scientist, that completed the project, gets Field Manipulation.png field manipulation expertise and 200 experience, or gets a level up if already had the expertise.
  • If the project is failed, superflare wipes out the colony and adds a modifier with -10% Mod habitability.png Habitability and -15% Energy.png Energy from jobs, that lasts for 20 years.

Pre-sapient Coexistence Events

These events can only happen on colonies that has coexisted with Pre-sapients for at least 10 years and are not uplifting them.

  • The pre-sapients damage some currency transfers antennas, bringing a -100 or -300 Energy.png energy credits loss.
  • Your presence agitates the pre-sapients. Driving them off will grant a small Unity.png unity reward. Xenophobe empires will gain Influence.png influence instead while Xenophile can investigate and earn a small amount of Society research society and Engineering research engineering research.
  • Xeno-researchers demand to be allowed to experiment on pre-sapients. Accepting will give you a moderate amount of Society research society research and -15% Mod pop happiness.png happiness for two years while refusing will add -20% Society research society output for two years. Xenophobe.png xenophobe and Fanatic Xenophobe.png fanatic xenophobe empires will gain Influence.png influence instead of the happiness reduction for accepting.