Complex sentence: M102 was observed by Méchain, who communicated his notes to Messier; later, it was admitted by Méchain himself that this object does not exist, and it was simply a re-observation of M101.
Split into simpler sentences: M102 was observed by Méchain, who communicated his notes to Messier. Later, it was admitted by Méchain himself that this object does not exist, and it was simply a re-observation of M101.