Chimera is an Earth-like world, with 90% Earth's gravity, freshwater seas covering 60% of the surface, and a slightly higher intensity of light from its closer orbit to a Sun-like yellow star. Chimera is incredibly rich with life, where even the coldest, hottest and driest climate zones support complex ecosystems. Chimera supports forms of life based upon multiple types of chemistry, and their interactions and evolution is an immense laboratory of biological warfare.
The two largest ecosystems are are based on the same organic matter and DNA as Earth life. One, however, has left-handed chirality, the other right-handed. The two ecosystems are at times locked in biological warfare, evolving powerful allergens and prions as defenses against those organisms evolved to consume both right and left handed proteins. At other times, they ignore each other, their biochemistry so incompatible conflict is pointless. Both of their remains are decomposed by tough, RNA based pseudo-fungi.
Right-handed life is the most Earth-like, with quadrupedal vertebrates and green plants. Left-handed life is the minority among plants and large animals, but has a virtual monopoly on niches associated with small, insect-like invertebrates. Few of these animals have evolved to metabolize right-handed plant proteins themselves, but many contain symbiotic bacteria that do the job for them.
Towards the poles, where temperatures regularly reaches -90 °C, a sparse ecosystem of silicon based life is spread across the ice. The plant-like organisms resemble crystalline mosses and lichens, interspersed with fractal silicate corals built by left-handed organic polyps. The silicon plants are energy-poor, and grow slowly, and the polyps small and well defended. The only other animal life to be found are migratory flyers and semi-aquatic organisms living along the shores.
Orbiting this unique world is a find that overshadows all others: an array of alien satellites. Observations from ground-based telescopes and orbital drones shows equipment suited to observing the planet and transmitting information out of the system. Interference or physical contact has so far been avoided for fear of unseen-defenses. the satellites are estimated to be thousands of years old, but orbital wreckage of older ones has been found, suggesting they are periodically replaced. The owners might show up for routine maintenance at any time.
The leading hypothesis is that Chimera's unique biosphere is a large and ancient science experiment, and that only one form of life arose there naturally, and the others were introduced. Preliminary fossil surveys show new types of life appearing during large-scale extinctions, which were presumably caused by the introduction of the new life. Perhaps the beings responsible for the satellites periodically introduce new forms of life, using the satellites to monitor their evolution and record anything of interest or potential use.