Galileo, 1995

Martin Tomasko

The Galileo experience was quite interesting. I wanted to propose an entry probe instrument for Galileo much like the Pioneer Venus instrument that would enter Jupiter’s atmosphere. When they announced the opportunity for Galileo, they said it was going into the daytime side, and we could study sunlight and the deposition of solar energy and do the same kind of thing for Jupiter as we did for Venus.

While they were reviewing the proposals, they decided they were going to change the trajectory and it was actually going to go to the night side. So we didn’t get selected, because we were working in sunlight, not with thermal radiation. But then about six months later they changed, and decided they were going to go to the daylight side anyway. So we were invited to submit the modifications of our proposal.

We submitted the modification and they said it had high scientific merit, and was really great, and they invited me to give a pitch to other co-investigators that they’d selected six months earlier for the mission. I gave my pitch, told them about my instrument, how big it would be and what it would measure. They asked the other investigators who thought this was a good instrument. They all raised their hands. Then the guy said, “Maybe I didn’t put that question quite right. We’ve already selected these guys and we’ve parceled out all the money. Who thinks that this instrument is so good that they’re willing to resign, get kicked off, so we can have room for Tomasko to fly his instrument?”

I was really annoyed. I thought, “If that’s the ground rules, why did you bother inviting me to do all this work? I just worked for months on this new revision of this proposal, and then you tell me that the only way you can add me is if one of these guys, who’s been working just as hard on his instrument, has to volunteer to resign?” That’s a hopeless situation.

Of course I didn’t get selected, but a guy got selected who had a thermal radiation experiment, analogous to my solar radiation experiment. That guy, in the meantime, had died. His instrument was given to another guy from Wisconsin by the name of Larry Sromovsky. I knew Sromovsky pretty well, and Sromovsky invited me to be a part of his thermal experiment, and to help calibrate his instrument.

The Galileo launch was delayed substantially because of the accident with the astronauts, the fact that Challenger blew up, and so Galileo kept getting postponed and postponed and postponed, and I was able to work with Sromovsky to a fair extent to save this thermal experiment, which had some problems; to make it work for the Jupiter entry probe.

So that was an exciting time, too. That instrument was a very difficult instrument. It measured thermal radiation and returned one number, but it turned out that that instrument was sensitive to all kinds of things. It was sensitive to the electrical charge; it was sensitive to humidity; it was sensitive to temperature and pressure. The joke was, it was a complete weather station, but it only gave you one number back. Sromovsky worked very hard to improve that instrument, and actually got some useful data out of it, but it was really only because it had been delayed so long.

Richard Greenberg

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.