Obsidian was a neutral planet in Sector 6. Its population, known as Pyroans, were all conditioned to be pacifists. The planet itself was in a crucial strategic location.
Geology and Climate
Obsidian's main feature was a single giant volcano in a permanent state of low-level activity. The Pyroan civilisation was largely subterranean as the atmosphere was not completely suitable for humans - possibly due to the volcanic gases constantly being expelled. There was plant-life on the surface but no sign of native animals.
The planet had been surveyed by the Federation, but, uniquely, not colonised or exploited by it, despite its key strategic location.
History
Obsidian had in fact been colonised by a group led by the scientist Hower, a dedicated pacifist. He believed humans could only survive with their aggressive responses removed and had conditioned the colonists to that end. The Pyroans had vowed to remain neutral and free or die. To this end they had buried a tremendously powerful nuclear device in the planets core and let it be known that, should any attempt be made to land on Obsidian, the bomb would be detonated. As a result, despite three major battles of the Intergalactic War occurring in the sector, Obsidian itself remained uninvolved in the conflict.
However, possibly as a result of the bomb's presence, every human on the planet was slowly dying from radiation poisoning. This aside, the Pyroans maintained a high level of technology, with sophisticated robot servants and possibly even a limited form of teleportation available to them.
The Liberator crew approached the Pyroans with an offer: they would protect Obsidian from the Federation if they could use it as a base. There was also a rumour, possibly deliberately started by Servalan, suggesting that Blake had visited the planet. However, Hower's son Bershar had already made an alliance with Servalan. A Federation battle fleet engaged the Liberator over Obsidian but was repulsed.
Federation troops had likewise boarded the ship but been repulsed, taking Cally and Orac with them. From Orac their commander learned the best approach course for an attack on the planet and supplied it to Servalan. However, as the fleet approached, the Pyroans detonated the nuclear device at the planet's centre, destroying it.