Ava's school planet is one of many man-made planets created for the sole purpose of schooling students in TITAN-run schools. The planet was inhabited by children and teenagers, who were relocated there after TITAN conquered their home planets and separated them from their parents.
These planets are artificial and created by TITAN for the specific purpose of relocating families from previously bought planets. The housing is incredibly cheap and most resources are quoted by Michelle as being "hand me downs",but the planet still has a viable core which is implied to have been harvested by the Silent Scavengers.
Ava's school planet was destroyed after Silent Scavengers quickly attacked and began stripping the planet of its resources and core.
- Ava cried when her schooling planet was destroyed because she had hoped her parents still lived there. Whether or not they actually did is a mystery, but Michelle has confirmed that they won't appear in future chapters.