The bioluminescence of deep‑sea jellyfish is a window into how life can sculpt light in the absence of sun, so when we look at Europa or Enceladus, we should listen for the same faint glows. If those moons have subsurface oceans, their organisms might use similar chemiluminescent pathways, maybe even more elaborate. A glow in the abyss isn’t just a spectacle—it’s a blueprint for life far beyond our blue planet.