We learn in The Expanse books that the Protomolecule was created by an advanced extraterrestrial civilization around two billion years ago and launched as one of the Bracewell probe swarms at trajectories towards stars harboring planetary systems
The protomolecule was first discovered on Saturns moon Phoebe by the Martian Congressional Republic in 0 XTE. It has remarkable abilities to radically alter infected life forms and utilize their biomass in various ways and even construct immense objects.. Following the descent of Eros Station to the surface of Venus in 9 XTE, the protomolecule began rapidly reshaping the planet.
In 12 XTE, the protomolecule launched a massive complex of structures just outside the orbit of Uranus and built a thousand-kilometer-wide object known as the Ring. It is a gateway to strange new worlds. The Ring network, or simply collectively referred to as the gates, is a complex ancient system of 1,373 artificially sustained traversable wormholes that connect planetary systems across the Milky Way galaxy.
An object traveling through a Ring treats the wormhole as a higher-spatial corridor between the linked points, effectively reducing transit times to near-zero. Sensor data, including visible light, behave accordingly, treating Rings as windows between two points, without being atomically harmed in any way.
The Sol gate was activated when Manéo Jung-Espinoza Books, a young slingshotter from Ceres, attempted to pass through it with his ship in order to impress his crush, Evita Jung. The second ship to pass through it was the Rocinante
As the show and the books begin to explore the nature of the thousands of worlds beyond the ring gate, we will learn more about the mysterious creators who built them, and their downfall. Season 4 of the show is based on Cibola Burn, the fourth novel in the series, and it marks a new narrative direction as the crew of the Rocinante explores new worlds beyond the Ring Gate on a mission for the UN.