Goodbye, Cassini
It was a dramatic end straight out of a science fiction thriller. As Cassini’s radio signal faded, then came back, and finally faded again for the last time, the early-morning watch party made up of students and professors in Beloit’s Sanger Center for the Sciences witnessed the end of an era. Cassini-Huygens, which had orbited the mysterious planet of Saturn to gather information for the last two decades, had signed off for good.
An international partnership between NASA, the European Space Agency, and the Italian Space Agency, Cassini had a mission that was extended twice: Its purpose was to learn more about Saturn by monitoring its seasons (each season lasts seven years) and its moons, like Titan, which has its own atmosphere.
Britt Scharringhausen, associate professor of physics and astronomy, hosted the 6:30 a.m. watch party (NASA is on its own time, she says.) She has been studying Cassini’s F Ring data since 2008 with her classes.
Q: How did you begin studying Cassini data about Saturn’s rings?
A: When Cassini data started coming down, I was already here at Beloit. I wasn’t on the Cassini team, but my graduate school advisor was. My advisor worked with the group that designed observations for the rings. No one was studying the rings from the side, and I have the computer model, which I created in graduate school, that shows what the brightest of the rings looks like from the side. He asked if I wanted the data. I was between research projects and I fell in love with the data.
Q: What data did you work with?
A: It was from two instruments [telescopes]: a visible and infrared mapping spectrometer (VIMS) and an imaging science subsystem (ISS). ISS had the narrow angle camera and the wide angle camera. I primarily study the VIMS data and my students are working on the narrow angle camera data.
Q: Why study Saturn’s F Ring?
A: It actually goes deeper into understanding how all of the planets formed, which was by collisional processes and gravitational attraction. In our solar system, this type of process is—as far as we know—only occurring on a day-to-day basis in the F Ring today. There are a lot of studies on how the F Ring works in 2-D, looking down from the top and assuming everything is more or less in one plane, but the F Ring is actually a three-dimensional place—more so than the other rings, because it is so much thicker. The third dimension is going to be important to understand collisional and gravitational processes in the F Ring.
Q: How many rings does Saturn have?
A: Seven. The main rings are the A Ring, B Ring, and the C Ring—the ones you see when you look at a picture. The F Ring is right outside of the A Ring, then there’s a D Ring, E Ring, and a G Ring.
Q: Tell me about the Cassini watch party.
A: We started at 6:30 a.m. and watched the NASA live feed. They had scientific journalists interviewing different scientists and engineers involved in the mission. At the very end, it was watching the radio signal being received by the telescopes on Earth through two bands—the X band and the S band. It was just sending back data on the health, position, and speed of the spacecraft. Cassini was trying to keep its antenna toward Earth and it lost the X band for a while, then both feeds were lost as it lowered in the atmosphere.
Q: I understand that some of your students have gone into graduate school partly because of the work they did on Saturn’s rings with you.
A: Morgan Rehnberg’12 just finished his Ph.D. at the University of Colorado-Boulder, working with Larry Espesito, the principal investigator on UVIS instruments on the Cassini mission to Saturn. The students who work with me learn about Saturn’s rings, of course, but they also learn the IDL programming language, which is popular among astronomers, and how to do photometry (measuring the brightness of things in astronomical images) and astrometry (measuring the positions of things in astronomical images), all skills that are valuable in internships, graduate school, and other types of jobs.
Sara “Alex” Sans’10 also got a Ph.D. from the University of Leuven in Belgium, studying stellar formation in forming galaxies using data from the Kepler spacecraft. She started her research on rings with me, but this shows how you can jump off from rings to distant galaxies!
Q: How did you feel when Cassini signed off? And since it’s been a few weeks, how do you feel about it now?
A: Cassini has provided us with a huge amount of data, much more than was planned for originally, due to some cool programming tricks that were learned during the Galileo mission to Jupiter and later uplinked to Cassini. We have enough data to dig through for a couple of decades. So, while it was sad to see Cassini go, we did so knowing it had exceeded our expectations in terms of new discoveries and new data to address interesting scientific questions.
Since then, I’ve found myself getting very excited about possible new missions to the Saturn system. There isn’t anything in the pipeline yet, but the community is talking about returning to Saturn’s moons, Titan and Enceladus. Saturn is a very challenging target because it is so far from the Sun. It requires a huge amount of fuel to get there, it takes a long time for the spacecraft to reach Saturn, you can’t use solar power, and you have to engineer to work in a very cold environment. But Titan and Enceladus are potential habitats for life: Titan because it has a thick atmosphere and a complicated hydrocarbon hydrological cycle, and Enceladus because it has a global subsurface liquid water ocean that actually comes up and out of the moon in the form of jets from the southern pole. I hope that Cassini data provide the impetus to go back to Saturn as soon as possible!
