Syllabus
The astronomy syllabus now follows the senior IOAA syllabus
The astronomy syllabus used to be transcribed from the Junior IOAA syllabus. It now follows the senior IOAA syllabus, because the OSN guide says OSN astronomy follows the IOAA syllabus.
The senior syllabus has no "space sciences" section or "cosmonautics" topic, so both are gone. The topics exoplanets and space-exploration moved to the sections where the senior syllabus lists them. Topic ids that existed before were kept, so materials, editorials and your planner are unaffected.