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The reason I got on the Galileo imaging team was because I made the case that the orbits and the spin of the satellites of Jupiter might play a role in determining what they look like, and that we might actually be able to use imaging to tell some things about how they rotated and stuff. I was the person on the team who understood dynamics. The other people who were interested in satellites were more geologists.
I had really brilliant students working with me. Randy Tufts was actually a student in Geosciences, but you know, no one cared. Greg Hoppa was a Planetary Sciences student. Paul Geissler was a former Planetary Sciences student. There were several other people who participated in the Europa stuff: Dave O’Brien, Terry Hurford. One other person who was important in all this was Alyssa Sarid. Alyssa was a Space Grant undergraduate intern who was assigned to work with me. She had some major breakthroughs in Europa work as well.
What was interesting was when the images came down the geologists used their expertise to try to interpret what they saw, to a large extent using qualitative analogies with the kinds of geological features that they were used to interpreting.
Our group had a much more quantitative approach. Randy Tufts brought expertise in geology, but we in general had a much more quantitative approach to interpreting the geology than most of the other team members, because I came from this orbital dynamics background.
What we looked at was the tides on Europa. Tides actually distort the shape of the body periodically. It causes heating—and that’s why there’s an ocean on Europa, because there’s enough heat to keep most of it melted—and it also, because it’s distorting abruptly the whole body, it stresses the ice on the surface so there’s cracks, and it also affects the rotation, and it affects the orbit. The tides are really important.
We were able to explain some very distinctive crack patterns on Europa in terms of the tides. In fact, our explanation of a certain kind of crack pattern called cycloids was the first evidence that really said, “There is liquid water there.” It was later corroborated by studies with a magnetometer that measured effects of Europa’s presence in Jupiter’s magnetic field and confirmed that there was a salty or conductive layer—a salty ocean. We just really were able to explain huge amounts of that. That was pretty exciting.
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