Characteristics
The planet has not been found to transit and, further, it is not likely to. It has also not been imaged. More specific physical characteristics such as radius, composition, and average surface temperature cannot be observed.
A dynamical study of planets b, c, and d showed tidal effects at least on b and c, to the extent that b had to be a sub-Neptune. All the planets from b to at least f must have migrated inward. That study implied that d was a sub-Neptune as well.
As such strong tidal forces often result in the destruction of larger natural satellites in planets orbiting close to a star, it is unlikely that HD 40307 d hosts any satellites.
Read more about this topic: HD 40307 D