Europa has a blue "city" icon above it. This is a mistake, marking Europa as a Settled Planet rather than a target for radiant quests like the other three Jovian moons.
The LCTN for Europa, SSol_PJupiter_MEuropa (0001B747) has the wrong keyword. Instead of LocTypeSettledPlanet (KYWD:0006F2F) it should have LocQuestUCR03World (KYWD:001E79B7). This removes the settled planet "city" icon and instead makes Europa available for radiant quests.
Maybe they originally intended to put a settlement there and it got cut (like a research facility around a black monolith), or more likely they copy/pasted the wrong key.
It's in the vanilla game. I corrected it as described above, by fixing the keywords.