Enceladus: sampling an alien ocean without landing via its plume

Enceladus, a small moon of Saturn, hides a global ocean beneath its ice and vents a plume of water vapor and ice grains through south-pole fractures, feeding Saturn’s E ring. Cassini flew through this plume from 2004–2017, sampling material from the ocean that had been altered en route and finding organic compounds and phosphorus, which points to habitability rather than life—no life-detection instruments were onboard. Future missions with dedicated biosignature instruments could probe further, but none are funded yet; current insights come from re-analysis of Cassini data and the plume’s status as a processed sample of an alien ocean.