Hessra was an ice-covered planet. Curiously, its thick ice was greenish-blue from chemical contaminants that had settled out of the planet's sour atmosphere.
It became historically important by the Cogitors prior to and around the time of the Butlerian Jihad. Because of its inhospitality, the Ivory Tower Cogitors chose that location to be perpetually secluded from all external events and interference.
The Cogitors remained on a stronghold on an exposed tongue of mountain high above a canyon. It was apartized of black metal towers and cylindrical protrusions with pointed domes. When Serena Butler visited the planet, a glacier had slanted and was beginning to enfold the towers.
Hessra was said to be located "near" Wallach IX.