Easter Eggs
Easter eggs are hidden references to other games or pop culture.
Natural Selection 2
The Natural Selection 2 Poster can be found inside the Wreck in the Grassy Plateaus and placed inside your Seabase. It is a reference to another game made by Unknown Worlds.
Portal 2
The first message broadcasted from the Communications Relay, which says: "This is an automated bounce back from the Aurora Mining Vessel. Your distress signal has been received. An emergency relief team will be dispatched to your location. *Static* Estimated arrival time: 9...9...9...9...9 hours". The wait time is a possible reference to Portal 2, whereas the announcer says to Chell: "You have been in suspension for nine...nine...nine...nine...nine..."
The Propulsion Cannon and Repulsion Cannon could also be references to two of the gels used in the game which are named Propulsion Gel and Repulsion Gel.
Holy Diver
A fifth message is received by the player's Communications Relay later in the game. The day this message is received varies. It displays: You've been down too long in the midnight sea. Oh don't you see what I mean? This message is a reference to the song Holy Diver by the US heavy metal band DIO.
Rimworld
The planet's moon bears resemblence to the moon from Rimworld, it can be noted that both moons are similar in appearence.