Bowman spends months around the ship by itself, slowly but surely approaching Iapetus. All through his tactic, he slowly notices a small black place around the floor of Iapetus, and later finds it similar in shape to TMA-1, only much bigger. The researchers on the planet identify this monolith "TMA-2", https://emilionvbfi.blogdanica.com/36453269/detailed-notes-on-2001-cash