Astronomy 241: Foundations of Astrophysics I
24. Satellites of the Giants
White House Astronomy Night: IfA Events
McCarthy Mall (near Hamilton): 11 am — 1 pm Solar Viewing Kapiolani Park (Zoo entrance): 7 pm — 10 pm Stargazing (Moon, Saturn) + 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 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