Final answer:
The retrograde orbit of Triton is not due to tidal forces, as tidal forces typically cause phenomena like geological activity and heating, as seen on Io, not orbital directions.
Step-by-step explanation:
The option that is not due to tidal forces is A) the retrograde orbit of Triton. Tidal forces are typically associated with phenomena such as geological activity and internal heating caused by the gravitational pull of a larger body on a smaller one, resulting in gravitational flexing and heating. For instance, the volcanoes on Io are a direct result of tidal heating due to Jupiter's strong gravitational pull. In contrast, the synchronous rotation of the Moon around Earth (C), the synchronous rotation of the Galilean moons (D), and the grooved terrain of Enceladus (B) are all effects of tidal forces. Triton's retrograde orbit around Neptune is believed to be the result of it being captured into orbit, likely originating from beyond Neptune's system, which is not a process directly linked to tidal forces.