Our solar system is filled with oceans. But only a few of those have captivated our attention.

During its 1979 Jupiter flyby, NASA’s Voyager 1 spacecraft found the surface of the moon Europa to be a cracked-up jumble of water ice, as if composed of icebergs floating atop some hidden sea. As the craft moved on to Saturn, it took measurements of that planet’s massive moon, Titan, and revealed the frigid world bore a thick atmosphere that could sustain lakes or seas of liquid hydrocarbons on the veiled, cryogenic surface below.

It took follow-ups by NASA’s Galileo mission that arrived at Jupiter in 1995, and later by the Saturn orbiter Cassini—a joint project between NASA and the European Space Agency (ESA)—to confirm this early evidence for extraterrestrial oceans. Galileo also hinted that two other Jovian moons, Callisto and Ganymede, perhaps harbored oceans as well. Cassini found abundant evidence of multiple ocean-bearing moons during its 13 years of studying the Saturnian system. In part because of these discoveries, both Galileo and Cassini were deliberately crashed into their respective gas-giant subjects, burning up in their atmospheres to avoid any chance of biocontaminating each planet’s promising moons. Galileo’s self-immolation occurred in 2003, and Cassini’s fiery end just unfolded on September 15.