The Abduction at Sylvia

The Abduction at Sylvia refers to the abduction of 30 million transhumans from their original Universe, severing contact with Earth and initiating the early multiversal era.

Background

As prospector satellites fanned out across the Sol System in the 22nd century and early mining rigs penetrated the outer layers of asteroid regolith, a clear picture of solar resources began to emerge that bore curious geochemical anomalies. Certain asteroids were found to be heavily depleted of platinum group elements and volatiles below the surface; in other places, patches of rubble turned up with metal alloy fragments of unusually uniform mixture ratio and other chemical abnormalities that to xenobiologists suggested artificial origin. In 2148, mining crews at Main Belt asteroid 752 Sulamitis located the collapsed remains of a structure buried in its caverns 1.5 kilometers beneath the surface, later identified as a possible industrial storage facility, and broke open the case in full.
87 Sylvia had long been noted for its twin moons, but habitat designers in the 21st century also eyed it for its strikingly low density. Three times lower than the density of typical solid rock, it suggested highly porous internal structure which, it was hoped, meant large internal caverns - and these hopes were answered conclusively in the affirmative when the geological surveyor mission Don't Touch That Dial reached Sylvia orbit in 2086 and laid down 36 seismic laboratories across a swath of its surface. Major mining operations began in the 2240s, although Sylvia's relatively great distance from the Sun (3.49 AU) limited its initial significance in the early interplanetary economy.
The asteroid's vast size made a complete survey of its caverns a difficult prospect, but in 2268, predicting growth potential, Hyundai Resources commissioned a dedicated team of over 100 geoscientists to create a comprehensive resource map of the interior, the first for an asteroid of such size. 14 days into the project, the team's seismometers located an arc of formations 45 kilometers below the surface of Micromegas Fossae with unusual reflective properties. 19 days in, the expedition crew breached the first chambers of the largest known city of the ___.