Planet 4, also referred to as the fourth planet, the Engineer Planet, and Paradise, is the planet that the USCSS Covenant, on its way to Origae-6, set out to explore after receiving a rogue transmission from its location. It is the presumed homeworld of the Engineers, and had at least one large city populated by the species.
Planet 4 is the fourth of five planets that are part of an unknown system located in an uncharted area of deep space known only as Sector 87. It has two moons of its own, each smaller than Earth's. It consists of 19.5% oxygen, 79.4% nitrogen, and 15.4 PSI in barometric pressure.
The planet's ecosystem was drastically altered by David when he unleashed the Chemical A0-3959X.91 – 15 pathogen on the Engineer's city. As a result of this event, all non-botanical life was either exterminated or used as an incubator for the gestation of hybridized predatory creatures such as the Neomorphs.
Before Davids' cleansing of Planet 4, the planet was populated with at least one city of Engineers. After David's experimentation with the pathogen, Planet 4 became home for the Neomorph species that were spawned from airborne spores released from mutated egg sacks, and for the Xenomorph species after David created Ovomorphs containing Facehuggers.
- While Planet 4 is not the official name given to the uncharted world by any of the crew on the Covenant, "Planet 4 / Main Theme" is the name of track 6 from Alien: Covenant's official soundtrack, which plays twice, in relation to the planet. The first is while Mother pinpoints this planet as the origin of the rogue transmission. The second is while the USCSS Covenant is on its way to the planet.