Galileo’s Swan Song: NASA Sacrificed a Probe to Shield Europa’s Hidden Ocean

In 2003 NASA deliberately crashed the Galileo spacecraft into Jupiter to prevent a potential contaminant from a drifting probe reaching Europa, after data suggested a subsurface salty ocean on Europa (and discoveries about other Jovian moons). The decision reflected planetary-protection rules: if a world could harbor life, a failing or abandoned spacecraft must not risk introducing Earth biology. Galileo’s extended mission delivered key findings about Europa, Ganymede, and Callisto, and its disposal set a precedent for how future outer-planet missions are planned to avoid contaminating ocean worlds like Europa.