The incident was discovered by Jim Holden and Miller to be a large-scale biological experiment by Protogen, where the infectious alien agent known as the protomolecule was unleashed on Eros' population.
The Eros project was orchestrated by Antony Dresden, executive VP of biological research at Protogen.
The incident at Eros got its start when Protogen was contacted by Mars to perform research on Thoth, Io and Osirus Stations. Groups of research teams were employed, drugged, and sent to their respective stations to begin work on researching and developing workable weapons and defenses against the protomolecule. One of the biggest research projects involved unleashing the molecule onto a massive life form, such as the entire population of a moon or planet; Eros was chosen. One of the many hundred scientists involved in this experiment was Paolo Cortázar.
Descent on VenusEdit
Although the formal research project was abruptly cancelled when the OPA boarded the Protogen research facility on Thoth Station and Miller killed Antony Dresden, it was far too late to affect the outbreak itself. The live feeds were then unlocked and it could be observed. Miller noted that the protomolecule was making noise that reminded him of mentally ill children singing to themselves, eventually saying coherent words. The OPA attemped to push Eros into the Sun by ramming it with the large spaceship the Nauvoo, but the protomolecule life-form aboard Eros Station had achieved sentience and control over the station's spin reactors, utilizing them by unknown means to maneuver the station in space, escaping destruction.
Eros travelled towards Earth, and although this was first suspected to be a malevolent action finishing the two billion year old objective of unleashing the protomolecule on Earth with Phoebe, Miller discovered that the infected body and mind of Julie Mao was at the center of the life-form, attempting to go back to her home planet.
Miller made contact with Julie and convinced her to crash-land on Venus, saving the Earth.
After crash-landing on Venus, the protomolecule spread across the entire planet's surface.
Eventually, after a little more than a year, the protomolecule on Venus became the Ring.
The plan to push Eros into the Sun by ramming it with the Nauvoo at high speed would not work in real life. To achieve this the amount of momentum transferred in the impact needs to precisely cancel the orbital momentum of Eros. At the speed of impact required Eros would shatter rather than be nicely stopped.
It would be more realistic, though less dramatic, to settle the Nauvoo against Eros and push Eros with the help the the Nauvoo's large drives. We would need to assume that the Nauvoo has a mass of several billion tons though, which is not consistent with the way she is described, as a large hollow cylinder.