A planet with an unbreathable atmosphere where Discovery set the trap that finally captured the Red Angel.
Essof IV is the planet Discovery travels to in The Red Angel because it offers enough energy to power the trap the crew devises for the mysterious time traveler. Michael Burnham, believed to be the Red Angel's focus, is deliberately left exposed in the planet's unbreathable atmosphere until the figure appears to save her.
Leland's Section 31 ship stands ready to close the wormhole behind the Red Angel, though Control attacks him from within his own systems. The trap works, the Red Angel revives the briefly dead Burnham, and Burnham recognizes the figure as her mother, Gabrielle.