Pluto is a rather interesting astral object. Once a planet, now a fairly large asteroid, it’s still the subject of more debate and more study than almost any other object out there (aside from the great planets, obviously). Despite this, it’s far enough away that most of the study hasn’t been able to reveal a lot of the fine detail, and so much of what goes on beneath the cold surface is a matter of some speculation, usually based on similar orbital bodies elsewhere in the solar system.
Simon Kattenhorn kicked the day off with a presentation on tectonics. I should probably define “tectonics.” It’s a field of study that is concerned with how the solid outer shells of worlds deform when they’re put under stress. There are people who study tectonics “in the field” by mapping tectonic structures that we can see like mountains and rifts and faults and folds, and there are people who study it by developing computer models to examine where these stresses come from and how they’re likely to deform rock or ice. Most people do both mapping and modeling. So it’s a field that combines pretty pictures, fieldwork, and physics, a combination I always loved.
So, back to Kattenhorn’s presentation. “Let’s start,” he said, “with what we know about the tectonics of Pluto.” His next slide showed the current best image of Pluto and was otherwise blank but for the text “there are difficulties.” Which earned him a laugh from the crowd.
Of course this was meant as an explanation of why in a meeting about Pluto Kattenhorn was going to proceed to talk about other icy bodies in the solar system, a common theme for the rest of the day. The idea is to compare the wide variety of icy moons and determine trends with size, composition, or solar system location, and try to infer from those trends what we might find at Pluto and Charon. Here’s a kind of old size comparison I put together of these bodies — I need to update it, not all of the sizes are the most up-to-date numbers, but it’s good enough to provide context. If you just consider size, note that Pluto naturally lumps in with the bigger icy moons including the Galilean satellites of Jupiter plus Titan and Triton, while Charon naturally lumps in with the mid-sized icy moons of Saturn and Uranus.
Read on for the rest of the article.