Reading: Chapter 11: Gas Giants “The avalanche has already begun, it is too late for the pebbles to vote.” Kosh, Babylon 5 Reading: Chapter 11: Gas Giants Chapter 12: Rings, moons, dwarf planets.

Structures within our solar system. Terrestrial planet/moons: Thin atmosphere over rocky crust over rocky mantle, over rocky (perhaps a liquid region) core. Jupiter/Saturn: H atmosphere over liquid H interior, over liquid metalic H, over rocky core. Icy (warm interior) moon: Ice crust over liquid ocean over rocky mantle over rocky core. Icy (cold interior) moon: Ice/rock mixture crust/mantle over rocky core.

Densities (in g/cc): Rocky worlds: 3.5 – 5.5 (Terrestrial planets ~5) Gas Giants: 0.7 – 1.5 Icy moons: ~2-3

As we go further away from the Sun, the solar system gets colder and colder.

Jupiter: 318 Earth masses 11 Earth radii Spins in 10 hours!

Quiz 5: Jupiter is made mostly of what element? A) H B) He C) Ice D) Rock E) Liquid

Saturn

Infrared view

Saturn's structure is very similar to Jupiter's. H clouds which thicken to liquid H over metallic H interior over a rocky core Density = 0.7 less than water!

Solar day = 10 hours 40 minutes 95 times more massive then Earth.

56 known moons

How would you describe Saturn's rings?

Saturn's Rings. * Are extremely thin: 200,000km across, but typically about 200m thick! * Made of millions of particles- but not very thick! -1cm to 10m in diameter -mostly ice or ice-covered rocks - all the ring material, compressed into a sphere would only be 100km across.

Shepherd moons shape the rings. But do they make them stable Shepherd moons shape the rings. But do they make them stable? An open question. Prior to Galileo’s study of the rings, it was thought they were about 200Myrs old and would only last another 200Myrs.

Uranus

Uranus Like Jupiter and Saturn, its atmosphere is mostly made of hydrogen. But its clouds are made of methane.

Uranus' structure New for us! * Mostly hydrogen atmosphere. Methane clouds * liquid/ice mantle made of water/ammonia/methane * rocky silicate core (like Earth's mantle)

Uranus spins on it's side! Ka-Boom Uranus spins on it's side! Its rings and its moons orbit its equator, which is nearly perpendicular to the ecliptic. But Uranus' magnetic field is tipped compared to its rotation. Perhaps Uranus was the victim of a huge collision in the distant past. The debris of which may have become its moons and rings.

Uranus has at least 21 moons, but only 5 are of reasonable size. All have densities of "dirty snowballs" between 1.3 and 1.6 g/cc.

Neptune

The main ring is less than 50km wide! Neptune also has rings! The main ring is less than 50km wide!

Neptune's structure is identical to Uranus' of hydrogen of liquid/ice water/ammonia/methane of rock.

Neptune has 14 known moons.

Time for icy moons.

Io, the innermost Galilean moon

Io, the innermost Galilean moon *Io is the most volcanically active body in the solar system! * There are no noticeable impact craters on Io. *The heating is generated by tidal forces (gravity).

Io's structure Density= 3.5 g/cc Terrestrial-like: thin, brittle rocky crust, a thick, molten mantle, and a solid, core made mostly of iron. Density= 3.5 g/cc

If you have volcanoes, you should also have what else?

If you have volcanoes, you should also have what else? An atmosphere!

Io has a thin, SO2 atmosphere. Io's atmosphere Io has a thin, SO2 atmosphere.

Europa

Smooth, cracked ice crust over an ocean Europa Smooth, cracked ice crust over an ocean

Europa has a vast under-crust ocean. Kept liquid by volcanic vents.

Europa's structure Europa has a thin (3 miles thick) crust made mostly of water-ice. Underneath lies a vast liquid layer of water, perhaps 30 miles thick. But most of the moon is made of rock, with perhaps an iron core. Density = 3.0 g/cc

Ganymede

Ganymede's interior Like Europa, Ganymede has a thin, mostly ice crust. Underneath is a thick, water-ice layer (mostly frozen). Under that is a rocky mantle surrounding an iron core. Density = 1.9 g/cc Like Europa, Ganymede has an extremely thin Oxygen atmosphere created by charged particles hitting the ice surface.

Callisto's structure Density = 1.9 g/cc Being the furthest moon from Jupiter and under the least tidal stress, Callisto did not have time to differentiate much before it became frozen. Density = 1.9 g/cc However, Callisto shows signs of a variable magnetic field, an indication of a subterranean, salty ocean.

Europa ~20-180 million years Structure changes as they get further from Jupiter. Surface Age: Io < few million Europa ~20-180 million years Ganymede ~3 billion years Callisto: 4-4.5 billion years old Density = 3.5 g/cc Density = 3.0 g/cc Density = 1.9 g/cc Density = 1.8 g/cc

Notice how prevalent water is in the solar system! Structure changes slightly as they get further from Jupiter. Notice how prevalent water is in the solar system! Europa, Callisto (liquid?) Ganymede, Moon, Mercury (ice)

Jupiter also has lots of smaller, irregular moons Jupiter also has lots of smaller, irregular moons. Jupiter has 63 moons in total.

Captured asteroids Large massive rocks in space with relatively thin (in height) atmospheres. Common structure: thin atmosphere over rocky crust, mantle, and core.

56 known moons