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This article is for the PC version of Stellaris only.

Exploration is one of the most important tasks for a spacefaring empire. At the game's start nobody will know anything about the universe beyond their home system. To learn more about anything beyond it, an empire will need to send their science ships out to survey them. Early game exploring is key for an empire to start growing rapidly, however caution is warranted for the various events and anomalies associated with exploring can bring either great boons or banes with them. Part of the Discovery tradition tree is focused on exploration.

Science ships

File:Mammalian Exploration.png
Mammalian science ship exploring a nebula system

Players can build science ships from the start of the game, and every player starts with a pre-built science ship which is ready to be sent out to survey. Every science ship must be assigned a scientist for the science ship to perform tasks such as surveying, assisting research of a planet, exploring uncharted hyperlanes or researching a special project (the ship can still move around without being assigned a scientist).

By default science ships are set to "evasive" stance, which means they will flee any system where hostile ships or spaceborn life forms are present. They can be set to "passive" stance instead, which lets the ship continue its current orders even if the system it is in contains hostile aliens.

Science ships cost 100 Alloys.png alloys. They are built at starbase shipyards, like all other ships. They do not have weapons but are automatically equipped with the latest sensors, engines, reactors, armor and shields based on your current technology. Science ship components are automatically upgraded as your technology advances without the need to refit them at shipyards.

Science ships can do the following actions, all which require a scientist to be assigned to the science ship:

  • Surveying gives detailed information about a celestial body, namely deposits, habitability and anomalies.
  • Researching Anomaly will investigate an anomaly, the investigation time being dependent on the level of the scientist and of the anomaly. For more details see Anomaly.
  • Assist Research allows science ships to boost the research output of the planet, by an amount depending on the skill level of the scientist.
  • Automatic Exploration requires the Tech automated exploration.png Automated Exploration Protocols technology and explores the galaxy automatically.
  • Experimental Subspace Navigation requires the Tech experimental subspace navigation.png Speculative Hyperlane Breaching technology and makes the science ship travel directly to any explored destination as MIA.


In order to survey a planet, select a science ship and right click on the planet and select the "Survey" option. The player may also select the "Survey System" option to order the science ship to survey every celestial body in the system. From the galaxy map, the player may queue survey mission by holding down "Shift" key and right clicking on a system and selecting the "Survey System" option one by one. The science ships can only survey systems that are within their reach. Science ships can be ordered to explore the galaxy automatically once the Tech automated exploration.png Automated Exploration Protocols technology has been researched.

Surveying celestial bodies such as stars, planets and asteroids allows for the discoveries of resources such as energy credits, minerals, strategic resources, research points or a primitive civilization or pre-sapient species on them. The player may then send a construction ship to build mining and research stations to harvest them, provided the system with the resources are within their borders. Starbase outposts can only be constructed in systems that have been fully surveyed.

Scientists may also come across anomalies (unusual things in the galaxy that require further study and analysis) when surveying a celestial body. These anomalies can be investigated by any scientist, but will be analyzed faster if the scientist has a high skill level. When an anomaly is found, the player gets an alert at the top of their screen. Clicking on this alert will bring up a screen which has the option to direct a scientist to research the anomaly immediately. The scientist will return to their current assignment once he or she has completed investigating the anomaly.

Planets surveyed by an empire within its own borders do not have to be surveyed by other empires. However planets within Fallen Empire borders will have to be surveyed once border access is gained one way or another. The same applies to Marauder systems in Apocalypse.png Apocalypse.

Situation log

A Typical Situation Log with events.

The situation log Normal sit log.png helps to keep track of special projects and anomalies, which are discovered when venturing out into the galaxy and exploring, and allows individual projects and anomalies to be tracked on the map. For democratic Governments it will also display Election Mandates. If there is an update to the Situation Log, it will glow in orange.Project pending sit log.png

Most projects are centered around a location (often a planet, but it could also be an object in space), and many of which requires the presence of a science ship with a highly skilled Scientist assigned to the science ship before the projects can be researched. However, some of the projects may require something other than a science ship such as a military warship, or a troop transport, or something else entirely. Some special projects are timed while others will remain present until resolved.

First Contact

Eventually ships belonging to another empire will be encountered. Diplomatic interactions will not be available until their language is translated so the only decision that matters is whether to attack unprovoked or to take a peaceful stance unless attacked. Hostile action can only be undertaken if the First Contact Protocol is set to aggressive (the default for Xenophobe.png xenophobe, Fanatic Xenophobe.png fanatic xenophobe, Militarist.png militarist and Fanatic Militarist.png fanatic militarist empires) and only with an explicit order. A hostile action will have a permanent -25 opinion towards that empire while capturing any of their worlds will mark it as a first contact war and give a permanent -75 opinion instead.

After the first contact the option to investigate and translate the language of the newly encountered empire will become available. Should you focus on other projects the alien empire will translate your language shortly after the encounter.

Note that the ethics-based replies available after a peaceful first contact do not affect opinion.

Galaxy Map

The layout of star systems is determined by the galaxy shape. All systems are connected by hyperlanes in clusters connected by choke points. The latter will never be a home system nor will they house anything that will stop an empire's expansion. The systems at the very edge of the galaxy will always be isolated, with a single hyperlane connection.

The number of choke points is set at galaxy generation.


Nebulae tend to have fewer habitable planets within them, but the chance of finding Strategic Resources is increased by 50%. Nebulae block all sensor coverage originating from other systems, meaning that it's impossible for an empire to see what is within and beyond a nebula's hyperlanes without having a ship or station therein. Nebulae are named and visible on the galaxy map from the start of the game.

Nebulae allow Starbases to construct the Sb nebula refinery.png Nebula Refinery building.

The L-Cluster

L-Cluster outside of a Huge-sized elliptical galaxy

Some Black Hole systems are home to L-Gates. These heavily modified gateways cannot be activated with the Tech gateway activation.png Gateway Activation technology. Upon first encountering one, the L-Cluster entry will be added to the Situation Log, requiring the collection of 7 L-Gate Insights. Insights can be obtained from investigating anomalies, defeating certain enemies, researching the rare L-Gate Insight repeatable Voidcraft.png Voidcraft technology or asking the Curator Order for an insight every decade (-5000 Energy.png Energy).

Once 7 L-Gate Insights have been collected, the technology Tech repeatable lcluster clue.png L-Gate Activation will become available for research. The empire will have to own a system with an L-Gate before it can access the L-Cluster. Finally, a special project will be added to activate the L-Gate, taking 180 days for a science ship to open the gate.

Opened L-Gates grant access to the L-Cluster, a cluster of stars located north-east of the galaxy and entirely inaccessible through the regular hyperlane network or experimental subspace navigation and too far for Psi Jump Drive range. The L-Cluster contains a unique Strategic Resource: Nanites. If a ringworld is built inside the L-Cluster, then while its construction will remove the planets in the system and make the original resources unavailable, the uninhabitable sections of the ringworld will contain some of the the resources instead as the habitable sections are completed, sometimes more than there were originally.

Once the first L-Gate is activated one of four things will be found, with the following weights:

Outcome Weight Opens all L-gates
Gray Tempest 50 Yes.png
Dessanu Consonance 30 Yes.png
Gray 30 No.png
L-Drakes 30 Yes.png

The outcome is rolled at the start of the game so reloading a previous save will not alter the result.

Up to 10 L-Gates can exist in a galaxy and new ones cannot be constructed. Only one L-Gate is located in the L-Cluster, in the Terminal Egress system, and as a result any L-Gate in the galaxy will connect to the same gate in Terminal Egress but the Terminal Egress gate can be used to travel to any L-Gate inside the galaxy.

Completed Sentry Arrays cannot grant vision of the L-Cluster before an L-Gate is activated. After that, it will grant visibility inside the L-Cluster as well.

Gray Tempest

Gray Tempest emerging from a reactivated L-Gate

A common outcome of the L-Gate activation is an invasion from the L-Cluster. All L-Gates in the galaxy except the first one activated will open at the same time and bring an invasion force. In a tiny galaxy with only one L-Gate the empire that activated it will endure the invasion instead.

If a Gray Tempest fleet bombards a colony for long enough it will turn it into a Nanite World. If the colony is a habitat or ringworld segment it will destroy them.

Nanite fleets are composed of one titan and 5 cruisers, all equipped with energy weapons and strike craft. As such, fleets with shields and point-defenses are the counters. Nanite ships have equal amounts of tier V armor and shields, making every offensive approach quite balanced.

The Gray Tempest home system contains a factory station twice as strong as the usual fleet that creates a new fleet every 10 years. If the factory is destroyed all Gray Tempest ships will dissolve and all Nanite Worlds will get the Terraforming Candidate planet modifier.

Dessanu Consonance

Another possible outcome of the L-Gate activation is finding an empire called the Dessanu Consonance inhabiting the entire L-Cluster. Upon discovery the Dessanu will provide the empire that opened the gate +1 Living Metal.png Living Metal, Exotic gases.png Exotic Gases, Rare crystals.png Rare Crystals and Volatile motes.png Volatile Motes. Their only request is that no ship will enter the factory trinary system at the heart of the L-Cluster and that they are not asked about the Nanites. The Dessanu will never leave the L-Cluster even if they become hostile, nor will they build new fleets.

Each time a ship or fleet enters the factory system the Dessanu will demand that it leaves within 60 days. Refusing to do so or inquiring too much about nanites will make them hostile, as will attacking them.

Each Dessanu system contains at least one Gaia World. However if a planet is successfully invaded and occupied it will turn into a Nanite World with the Terraforming Candidate planet modifier. All armies will safely retreat back in orbit. If the factory is destroyed the same will happen to all Dessanu worlds.


If the L-Cluster is abandoned a random Nanite World will have a Level 3 Surface Signature anomaly. Investigating it will reveal a nanite entity taking the form of a member of the species discovering it. Asking it to join you will add Gray to the Contacts menu. Gray can take three forms at any time:

  • Governor Level 10 leader with the Leader trait psionic chosen one.png Nanite Entity trait
  • Nanite titan
  • Nanite Warform army

Should Gray be destroyed it will merge back in 10 years.

This outcome leaves only one L-Gate activated, all the others coming online afterwards one every one or two years. This gives the empire that activated the first L-Gate a significant headstart.


The only outcome of the L-Gate activation seemingly unrelated to nanites is the spawning of L-Drakes. Each L-Gate in the galaxy will activate and bring an L-Drake which will travel to a random system three hyperlanes away and nest there. It will not be hostile even if its nesting system is claimed. If an L-Drake is attacked all L-Drakes will become hostile towards the attacking empire but each L-Drake killed adds a moderate reward of Influence.png Influence and Minerals.png Minerals. If the empire that opened the L-Gate takes this stance it will also gain moderate Engineering research Engineering and Society research Society research for each killed L-Drake. L-Drakes fight identically to the Young Drake from the Leviathans.png Leviathans DLC.

If the empire that opened the L-Gate enters a nesting system with a science ship it will have the option to start a special project to tame the L-Drake residing there, gaining control of it. The option is not available if the empire is Fanatic Xenophobe.png Fanatic Xenophobe or Civic fanatic purifiers.pngCivic devouring swarm.pngCivic machine terminator.png genocidal.

This outcomes leaves all L-Gates activated and leading to an abandoned L-Cluster, allowing everyone access.

Habitable Worlds Survey

Habitable Worlds Survey is an event that takes place every game and can start at any point after alien life of any sort has been discovered. Gestalt consciousness.png Gestalt Consciousness empires do not get the event.

Accepting the event will issue a special project that requires surveying any 8 habitable planets. The task is completed especially quickly on games with a higher percentage of habitable worlds set up. Completing the event will grant up to 500 Energy.png Energy and Society research Society research. Refusing the event will grant 20 Influence.png Influence instead.

If the Habitable Worlds Survey special project has been completed a few years later the Alien Specimen Procurement event will start. Accepting it will issue a special project to collect specimens with a Science Ship on all 8 surveyed planets. Each time a specimen is collected it will grant a small amount of Society research Society research. Completing the event will grant a moderate reward of Energy.png Energy, Society research Society research, Influence.png Influence and Unity.png Unity.


Game concepts
Governance EmpireEthicsGovernmentCivicsPoliciesEdictsLeaderFactionsPopulationSpecies rightsEconomyTechnologyTraditionsCrime
Exploration ExplorationMapSpeciesAnomalyEventsFTLFallen empirePre-FTL speciesPrecursorsSpaceborne aliens
Colonization ColonizationCelestial bodyPlanetary featuresPlanetary managementDistrictsBuildingsShipStarbaseMegastructures
Diplomacy DiplomacyTradeSubject empireFederationsGalactic communityAI personalities
Warfare WarfareSpace warfareLand warfareShip designer
Others TraitsTerraformingPop modificationSlaveryCrisisPreset empiresAI playersEaster eggs