Astronomy 241: Foundations of Astrophysics I 15. Satellites of Giants + 59 more Inventory of Moons • 6 large moons (D>1500 km) + 53 more — most internally active • 12 medium (D>300 km) — some activity in past? + 22 more • 145+ small (D>1 km) — no internal activity + 11 more Large & Medium Moons • spherical due to self-gravity • composed of ices & rock • most* formed in disks around parent planets • most* orbit in same direction as planets spin Triton is exception! The Jupiter Satellite Page Irregular Satellites of Jupiter • prograde: dashed • retrograde: solid The Jupiter Satellite Page Activity: Galilean Satellites IO EUROPA GANYMEDE CALLISTO Wide range of geological activity: — Io is most volcanic object in solar system! — Callisto exhibits very little activity. Ganymede and Callisto Global Callisto in Color Ganymede has a mixture of Callisto has a old and very old and new terrain, and hints heavily cratered terrain, with of tectonic activity. a possible subsurface ocean. Europa: an Ice-Covered Ocean? Fractures in crust Pwyll: Natural and False Impact Color Views of Europa crater Exaggerated colors “Natural” colors Europa: Rafts of Ice Europa - Ice Rafting View Europa: Internal Structure What warms Europa’s subsurface ocean? Io: Volcanic Moon Loki Patera: active center Pele: Io’s largest volcanic pluume Topography and Volcanos on Io Io: Volcanic Moon Ongoing Volcanic Eruption at Tvashtar Catena Tvashtar’s Plume Why so active? Tidal Heating of Io Jupiter Io is alternately stretched and squeezed in its elliptical orbit around Jupiter, creating heat through friction. Over time, this friction should make Io’s orbit more and more circular; what keeps Io’s orbit elliptical? 2:1 Mean-Motion Resonance m1 m2 M 2:1 Mean-Motion Resonance m1 = 0.001 M m2 = 0 P1:P2 = 2:1 2:1 Mean-Motion Resonance Laplace Resonance: Io, Europa, & Ganymede 4:2:1 Mean-Motion Resonance Small Satellites of Saturn • too small to be spherical • orbit both directions! Titan: a Moon With Atmosphere Thick smog of N2 and hydrocarbons (CH4, C 2H6, etc)! Hydrocarbon Lakes on Titan Reflection of Sunlight off Titan Lake Radar Shows Evidence of Seas Meandering Riverbeds on Titan Xanadu's Meandering Rivers Titan’s Climate • Surface temperature: 94° K (-179° C) • Clouds of CH4, C2H6, other hydrocarbons • CH4 falls as rain, forms rivers & lakes • Seasonal changes in CH4 lakes • CH4 replenished by cryo-volcanism Wikipedia: Titan .