Protomolecule

In 2342, a Martian scientific survey crew on a routine mission to explore Saturn’s moons made a landing on Phoebe. Drawing core samples to see if ice might be mined from the moon as it was from the planet’s rings, the scientists found unexpected silicate anomalies. To investigate the mystery, the Martian government contracted the Protogen to operate a research facility on the moon.
Protogen was quick to discover answers that it kept secret, even from its Martian partners: the entire moon was in fact an object that had arrived from outside the solar system billions of years ago, captured by Saturn’s gravity before it could reach its true destination, Earth. What’s more, deep inside the planetoid Protogen found what they believed to be the payload Phoebe was intended to bring to Earth: an adaptable set of encodings able to replicate and manipulate matter at a molecular level. Set free, Protogen believed these would have used early life on Earth as raw materials, rebuilding and replacing it with whatever was desired by its creators. Though the origins of the planetoid and the final goals of those who sent it were a mystery, Protogen recognized the power of the tool they had discovered and gave it a name: the protomolecule.
Protogen’s plan to investigate the power of the protomolecule was quick and increasingly ruthless. First, they trapped their Martian partner scientists in a lab on Phoebe and exposed them to the protomolecule. When that failed to provide enough data due to lack of raw genetic material for the protomolecule to transform, Protogen destroyed the station to hide their tracks, framing the OPA for the damage. They then framed Mars for an attack on an Earth ship, to spark tensions between the two planets and distract them from Protogen’s actions until it was too late. Setting up a secret lab on Eros Station in the Belt, they unleashed the protomolecule upon the station’s population. Finally free to pursue its agenda, the alien molecular machine painfully and horrifically transformed all 1.5 million people on the station.

In charge of Tycho Station and its construction projects, the OPA tried to use the enormous bulk of the generation ship Nauvoo to push Eros into the sun to destroy the protomolecule—only to have the station suddenly and impossibly dodge the approaching ship. In apparent defiance of everything humanity knew about thrust, momentum, and acceleration, the asteroid began moving—towards Earth. A desperate attempt to destroy Eros using Earth’s entire arsenal of nuclear missiles not only failed when Eros somehow cloaked itself against all conventional sensors, but left the missiles under the control of the OPA, enormously increasing the Alliance’s military might.

In the end, Earth was spared by two people, a missing young woman who had been one of the protomolecule’s first victims, the “seed crystal” of its growth on Eros, and the Belter detective hired to find her. Although they were both absorbed by the protomolecule, together they managed to have enough influence over it to guide the asteroid to a crash landing on another world in the system: the uninhabited planet Venus. Thick clouds closed in over the impact site and the protomolecule continued its mysterious work on a planetary scale, raising mysterious crystalline towers and making flickering, ghostly lights visible to probes. Everyone now knew that humanity was not alone in the Expanse.