Moons, Rings, & Dwarf Planets Solar System Astronomy Chapter 11

In the Solar System: Dozens of worlds Rock & ice Diverse properties, only partially understood Offers insight into our ideas/theories of planet formation

Moons Most larger moons formed with planets Regular moons Some are captured objects Usually in retrograde orbits Irregular moons

Major Moons Four gas giants Earth Some are geologically active Others show evidence of past activity

Many Moons

Formation of Large Moons The largest moons formed the same way the terrestrial planets did Major processes: accretion and differentiation Biggest difference with the terrestrials: composition more ices (frozen water, methane, &c) less rock (silicates)

Rings All four gas giants have ring systems Swarms of tiny moons Saturn’s are the largest and brightest Particles orbit according to Kepler’s laws orbits are circular collisions or ring gravity keep them that way

Saturn’s Rings Very complicated system thousands of ringlets bright and dark rings, and “gaps” gaps are not empty brightness/darkness indicates amount of material in each ring system is extremely thin

Rings Rings don’t contain much material mass of all the ring particles is about the same as a small, icy moon Can be distorted by the gravity of nearby moons

Origin of Rings Ring material is from disrupted moons Large moons are broken up within Roche limit Tidal forces Other sources of ring material Volcanoes Impacts Saturn’s rings formed from an icy moon Uranus’ and Neptune’s are very dark Body rich in carbon

Moons & Rings Rings don’t last forever Collisions and sunlight would destroy them Small, nearby shepherd moons can help stabilize Moons also create gaps orbital resonance: orbital period is in a ratio with the moon period

Titan Saturn’s largest moon deep, nitrogen-rich atmosphere Currently being explored by the Cassini spacecraft Huygens lander revealed icy “rocks” and a soil rich with organic compounds

Titan Saturn’s largest moon deep, nitrogen-rich atmosphere methane and ethane can condense and lead to rain of methane and ethane Methane is gradually converted to ethane in the atmosphere  Renewed in active geology

Then there’s poor Pluto… Very small 1/6 the mass of Moon Binary planet: moon Charon properties like comets eccentric orbit icy composition (probably) member of the Kuiper Belt Objects (KBO) Probably not even the largest

Discovery of Pluto 1930 Clyde Tombaugh Existence predicted from disturbances of Neptune Though it’s too small…

Discovery of Pluto

Venetia Burney Venetia Burney Phair died April 30, 2009

Pluto Orbit 2:3 resonance with Neptune Comes closer to Uranus than Neptune

Dwarf Planets Small numbers, but increasing Pluto Charon, Nix, Hydra Eris Dysnomia Ceres Haumea Hi’iaka, Namaka Makemake