In contrast to the eerie and unsettling music that plays in the Frigate Orpheon before its crash, this theme is soothing and calming, completely altering the tone and mood of the sunken ship to suit the new underwater setting. It primarily features piano melodies and harmonies, accompanied by various atmospheric synth effects.
It is titled Wrecked Ship Frigate Orpheon (墜落船フリゲートオルフェオン) on the Metroid Prime & Fusion Original Soundtracks, or simply Crashed Orpheon (クラッシュオルフェオン) on the Nintendo Sound Selection Vol. 1: Healing Music album. The track is also included in the Samus Archives Sound Selection CD, which is packaged with the Special Edition of Metroid: Samus Returns.
Crashed Ship can be heard here: