Syrenya was the fourth planet in the Adonolo star system in the Orion Neutrality Area in the Alpha or the Beta Quadrant. It was the only class M planet in its system, and it had three moons. It was home to an Orion colony.

Syrenya was originally a harsh world of stony plains with a carbon dioxide atmosphere. Its parent star, Adonolo,, was a hot blue-white Type B7 sun, so with an axial tilt of 31.2 degrees, temperatures on Syrenya reached 100 °C during summer and dropped to -100 °C in winter. Bacteria and lichens were all that could survive in these conditions.

Roughly 13,000 BCE, the Pergue race tried to terraform Syrenya and make it habitable, but the effort was an utter failure. After the Orions managed to repair their homeworld of Botchok during the First Stage (concluding in 7730 BCE, reference stardate −97/30), the impressed Pergue imported Orion slaves to terraform Syrenya for them, through the Syrenya Development Company. To do this, the Orions imported an ocean at an incredible cost, transporting ice from asteroids and waste worlds and launching it into the atmosphere during winter. This included ammonia ice to add nitrogen for biological processes. The repeated asteroid impacts pulverized the rocky plains, which could then be seeded with moss, microbes and worms to create fertile soil.

This process took a thousand years to complete, but by the end, Syrenya had become a habitable Class M world, reaching a self-stabilizing phase around 4800 BCE. The carbon dioxide atmosphere had become a terrestrial one, balanced with oxygen and nitrogen, while the water oceans averaged the extreme temperatures. This was the oldest completely documented example of terraforming known to 23rd century research (records of the First Stage terraforming of Botchok were fragmentary). The terraforming never needed adjustments after that, but the world remained relatively harsh and tropical.

The Orion slaves themselves also thrived, and survived into the late 23rd century, with a population of 900 million. The world was still governed by the Syrenya Development Company, with shares controlled by ten powerful Orion families. Together, they ensured a smooth and functioning society, with a proud and hardy people. The Orion saying "as proud as a Syrenyan" meant that one had truly earned their pride.

Syrenya had a tropical climate, a class M terrestrial atmosphere and a 27-hour-day. It had a total surface area of 331,352,880 square kilometers and, with 32% land mass, a total land area of 106,032,920 square kilometers. Syrenya was made up of 4% normal metals, 21% radioactive elements, 12% gemstones and 3% special minerals, with trace amounts of industrial crystals.

It had a technological/sociopolitical index of 999974-74 and a planetary trade profile of EFBDCDE/A(A) (FASA RPG module: The Orions: Book of Common Knowledge).

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