Robert Poppalardo: We didn’t know 'til today that there’s evidence from years ago that there’s something there. Europa is one of the most fascinating bodies in the solar system. We think beneath its icy surface is a global ocean twice the volume of all of Earth’s oceans combined. In the late 1990s, the Galileo spacecraft explored the Jupiter system. It made about a dozen flybys of Europa. It took observations from its cameras and from its magnetometer.

Margaret Kivelson: By discovering that there was an induced magnetic field at Europa, we were led to the conclusion that there must be an ocean just beneath the icy surface of the moon. But there were some strange signatures in the magnetic field that we had never really been able to account for.

Poppalardo: Images of Europa from the Hubble space telescope have hinted at gases that might have come from plumes erupting at Europa.

Kivelson: The Hubble images had given an estimate of the height and width and I knew how fast Galileo was moving relative to Europa.

Poppalardo: There are better tools now...better computational techniques...better computing...that we can go back and look at that old dataset anew.

Kivelson: So, my colleague Xianzhe Jia set up a calculation to see what would happen in the environment of Europa if there were such a plume. And when he ran this simulation, it agreed just beautifully with the data that we had collected.

Poppalardo: Reanalysis of the Galileo magnetometer data suggests that the Galileo spacecraft, on its closest flyby of Europa, flew through a plume. The Europa Clipper mission is going to explore Europa to investigate its habitability. If we find active plumes, then we can sail on through them and sniff and taste that stuff that’s in the plume. We can analyze the particles and the gases to get at the detailed composition of Europa’s interior.