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 Satellite Page Activity: Galilean Satellites

IO GANYMEDE CALLISTO Wide range of geological activity: — 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