This is unusual for a large moon, as many others, like Ganymede and Io, do have magnetic fields. There are a few possible reasons for this:

* Slow rotation: Triton rotates very slowly, which could hinder the generation of a magnetic field through the dynamo effect.

* Lack of internal metallic core: Triton might not have a large, metallic core that could act as a conductor for the dynamo effect.

* Geological activity: Triton may have a relatively inactive interior, lacking the necessary heat and movement to create a magnetic field.

However, there is some evidence of a weak, induced magnetic field around Triton. This is caused by the interaction of Triton's ionosphere with Neptune's magnetic field.

So, while Triton doesn't have its own substantial magnetic field, it does experience a faint, induced one from Neptune's influence.