NASA has proposed several missions to explore the moons of Jupiter and Neptune, but unfortunately, these missions were not approved due to various reasons such as funding constraints, technical challenges, and prioritization of other missions. While it's difficult to say definitively what we might have learned from these missions, here's a glimpse into some potential scientific Erkenntnisse:

Jupiter's Moons:

1. Europa's Habitability: The proposed Europa Clipper mission aimed to investigate the potential habitability of Jupiter's moon Europa. By studying its ice crust, subsurface ocean, and composition, scientists could have gained a greater understanding of whether conditions exist that could support life.

2. Ganymede's Interior and Magnetic Field: The canceled Jupiter Europa Orbiter mission would have explored Ganymede, the largest moon in the solar system. It could have provided valuable insights into its internal structure, composition, and the unique magnetic field that surrounds it.

3. Callisto's Surface and Composition: The Europa Jupiter System Mission (EJSM) proposed a lander mission to Callisto, the outermost Galilean moon of Jupiter. This mission could have shed light on the moon's surface characteristics, composition, and potential for subsurface oceans.

Neptune's Moon Triton:

1. Origin and Evolution: The proposed Trident mission to Neptune and its moon Triton aimed to unravel the moon's origin and evolution. Scientists believe Triton might be a captured Kuiper Belt object, and this mission could have helped determine its origins and interactions with Neptune.

2. Geysers and Atmospheric Activity: Observations from Triton's geysers could have revealed valuable information about the moon's internal processes and the composition of its icy surface. Studying its tenuous atmosphere could have also provided insights into its interaction with the solar wind.

3. Cryovolcanism and Surface Features: Exploring Triton's surface up close would have allowed scientists to examine unique features such as its "cantaloupe terrain," which could provide clues about cryovolcanic activity and geological processes on the moon.

While these proposed missions did not come to fruition, they represent the scientific community's ongoing fascination with exploring the diverse moons of Jupiter and Neptune. Future advancements in space exploration technology and funding opportunities may eventually allow for these missions to be revisited and potentially turn our hypothetical Erkenntnisse into scientific discoveries.