After a brief discussion of how Saturn’s ring material is an excellent model for planetary disks (like the one that formed our own solar system 4.5 billion years ago), we briefly talked about the F ring and ring spokes. I was gratified to learn that we are starting to see spokes form, as expected around equinox if they are enabled by low sun-angle solar illumination on the rings, but my eyes widened when I asked Linda about the latest genesis theory of the spokes. I had never heard of the possibility spoke formation might be related to Saturnian storms or even lightning—boy, the things you learn from a ring scientist! As cool as spokes are, I quickly forgot about them when Linda reminded me that the F ring’s little pickpocket, the tiny moon Prometheus, is preparing for its deepest dip into the F ring itself late this year, when the Prometheus apoapse will line line up with the F ring periapse. What gravitational mischief will this wee satellite impart during this interaction? I plan to stay tuned as Linda and her colleagues piece together the mysteries.
With all this amazing ring science in the bank, I was humbled to realize the best days for ring science may be yet to come, even as soon as next week! During Saturn’s equinox around August 11, 2009, Cassini scientists will be busy tracing the shadows of Saturnian moons on the rings, looking for ring warping. Some of the biggest ring particles themselves may actually be able to cast shadows on the rings, too! The thickest portion of the B-rings (still no more than a few tens of meters in thickness) will see sunlight for the first time in nearly fifteen years—how quickly will they heat up and what does that tell us about their size and composition? Not only does Cassini have a front-row seat for this spectacle, this equinox is more important than ever, because the show on the third rock has been preempted this year by Saturn’s solar conjunction. That is, we on Earth will not be able to observe the fireworks of equinox at Saturn, because the ringed planet is nearly behind the sun as seen from here. How fortunate we are to have an awesome orbiting asset waiting to capture this rare celestial event!
I asked Linda when she first saw the rings of Saturn, and she couldn’t quite recall. She did mention she obtained her first telescope in third grade and was soon chasing down the moons of Jupiter, excitedly yelling to her mom to come see the spectacle. I’m sure with such early proficiency with the telescope, her first view of the ringed planet was not far behind. I remember watching Linda on PBS specials about Voyager in junior high and high school, dreaming of working at JPL, but never dreaming I’d be sitting in the office of one of my heroes, being treated as a peer. Good luck with equinox, Linda! I can’t wait to catch your contagious excitement when the first images come to Earth, as I’m always able to do after hearing you speak.