I Remember You Well
The first time I “met” the Saturnian moon Enceladus was during the Voyager 2 flyby in August, 1981. I was a wet-behind-the-ears science writer/editorial assistant at The Denver Post, and somehow I got the managing editor to send me out to JPL to cover the mission. I had an idea there was a “local angle” and that I’d pursue it. Turns out there was–a guy named Jim Warwick at the University of Colorado had a planetary radio astronomy team hooked up to the Voyager mission, and so I hooked on to him as a sort of science guide. It was fateful.
The first closeups of Enceladus came a day or so into the flyby, and when they appeared on the TV screen in the Von Karman auditorium at JPL, we were all entranced by the details. This was quite a moon! Cratered, cracked, covered with strange grooved areas. I was hooked on planetary science for life!
Last week, the Cassini Mission at Saturn flew REALLY close to Enceladus, looking to study the polar regions. It flew through some icy water plumes jetting out from fractured, geyser-like openings in the south polar region, and took some time to look around the north pole area, which has also been modified by geysers and cratering in the past.
This image shows this icy moon’s north polar region, and a LOT of evidence for internal activity (driven by heat). The surface is cratered, sure, but those craters have disrupted regions that were resurfaced sometime in the distant past. And, some flow-like formations seem to have gone right through some craters. What would be resurfacing Enceladus? One explanation is tectonism, surface activity driven by heating from within.
Since Enceladus is largely ice with a rocky core, heating from below the surface could easily melt the interior ices. Eventually that melt is forced out through cracks in the surface–where it acts as a kind of repaving material. Incoming impactors AND pressure from below continue to disrupt the surface, and you get these terrains where craters are interrupted by flow features and smooth plains are torn up by craters. It’s quite an interplay of planetary activity and surface modification out there. The next step is to figure out the timeline for these activities. Obviously Enceladus is undergoing resurfacing pretty often, given that there are geysers shooting out material around its south pole. But, the big question now is, “How long ago was the north polar region active?” Stay tuned!
Now, that’s just darned cool. The spacecraft “saw” something on either side of Rhea. This is very much like the first time Galileo Galilei “saw” something he took to be “ears” or “handles” on either side of Saturn as it appeared through his telescope in 1610. So, it’s kind of fitting that a modern-day descendent of his telescope (albeit a different kind of detector) found rings around Rhea.