Helios 2a

Tangaroa's only moon - Helios 2a is a 'fast orbiting' moon with a dense nickel/iron core. The low density of the ocean planet combined with the moon's unusual orbit give rise to frequent and unpredictable volcanic activity on Tangaroa, ultimately causing terrestrial islands to form and then be reclaimed by the sea rapidly.

This moon doesn't appear in the earlier iterations of the starmap and was added in 2017.