The long-dead Galileo spacecraft may have flown right through a plume of water spurting up from the surface of Jupiter’s moon Europa. A new analysis of 20-year-old data shows just that, adding evidence that the much-contested fountains actually exist there.

In the late 1990s, the Galileo probe detected an unusually warm area on Europa’s surface. Astronomers connected that anomaly to a potential plume of water emerging from the moon’s subsurface ocean. In recent years, images from the Hubble Space Telescope have also shown …