as101 lesson 12

Major moon composition

Many Jovian moons are mixtures of rock + large amounts of ice (mostly water ice; some ammonia/methane ice)

Moon size groups

Small

Large/medium moon orbits

Usually circular, near equatorial, prograde; formed in mini-nebulae around planets

Galilean moons

Io, Europa, Ganymede, Callisto (4 largest moons of Jupiter discovered by Galileo)

Galilean common traits

Large, spherical, formed around Jupiter, mostly rock + ice, geologically important

Io composition/features

Rocky interior; sulfur-rich surface; most volcanically active object in solar system; few craters

Why Io active

Tidal heating from Jupiter + orbital resonance (1:2:4 with Europa/Ganymede influences)

Europa composition/features

Ice crust over likely global liquid-water ocean; rocky core; cracked smooth icy surface

Europa key significance

Possible subsurface ocean may support life

Ganymede composition/features

Rock + ice; largest moon in solar system; cratered + tectonic regions

Callisto composition/features

Rock + ice; heavily cratered ancient surface; less geologically active

Uranus moons (know 4+)

Miranda, Ariel, Umbriel, Titania, Oberon

Uranus moon naming theme

Named after sprites/spirits and characters from Shakespeare (and literary tradition)

Neptune largest moon

Triton

Why Triton

backward moon

Triton origin

Likely captured Kuiper Belt object

Saturn rings

Most prominent ring system in solar system; thin flat rings made mostly water-ice particles + dust/rock

Main Saturn rings

A, B, C rings

Major gap

Cassini Division between A and B rings

Other gap

Encke Gap in A ring

Ring thickness

Extremely thin; about <100 m (many places <30 m)

Ring width

Extend hundreds of thousands of km outward

Ring origin

Likely broken moon/comet material inside Roche limit where Saturn’s tidal forces tear bodies apart

Roche limit

Distance where planet’s gravity can pull moon apart into ring particles

Why rings stay organized

Particles orbit Saturn; resonances with moons shape gaps/structure

Shepherd moons

Small moons whose gravity keeps narrow rings/ring edges confined

Examples shepherd moons

Prometheus + Pandora shepherd F ring

Cassini Division cause

Orbital resonance with moon Mimas

All Jovian planets have rings

True, but Jupiter/Uranus/Neptune rings are faint/dark compared to Saturn

Dwarf planets common traits

Orbit Sun, nearly spherical, have NOT cleared orbital neighbourhood, smaller than classical planets

Official dwarf planets (core)

Pluto, Ceres, Eris, Haumea, Makemake

Pluto location

Kuiper Belt object beyond Neptune

Why Pluto not a planet

Did not clear its orbit; shares region with many Kuiper Belt objects

Kuiper Belt

Region beyond Neptune (~30–50 AU) with many icy bodies

Ceres location

Asteroid belt between Mars and Jupiter

Pluto traits

Small, icy, eccentric/inclined orbit, multiple moons, dwarf planet

MC/T-F trap

Pluto is still a planet