JAXA selected MIO as the new name for the Mercury Magnetospheric Orbiter (MMO) to be launched this Japanese fiscal year. The selection process was based on public response to the MMO renaming project made during the designated correspondence period, Feb. 20-April 9, 2018.
The definition of the word mio in the original Japanese is a waterway or fairway. It is a fitting name denoting how far the MMO mission has come, navigating its course past important research and development milestones. It also carries the connotation of wishing the spacecraft a safe journey.