Note the different scale of the inner and outer solar system. Note that Mercury and Pluto have the largest orbital inclinations. Note the tilts of the different planets (Venus upside down, Uranus sideways). We used to think these were due to giant impacts (and maybe they are), but recent work has also shown that frictions between core, mantle, and atmosphere can lead to large tilt changes. The Moon may act to stabilize the Earths tilt. 

This is mostly to discuss relative sizes. Jupiter and Saturn are true gas giants; Uranus and Neptune are more like “ice giants” (though with deep gaseous exteriors). Can mention that it takes a core about the size of their cores to attract gas directly from the solar nebula (which needs to be defined).

Point out the clouds, whose colors come from organic chemicals we don’t fully know. Note that “organic” means compounds with H,C,N,O, not “live”. Shadow of Io. Red Spot. Bands. Other smaller storms (white ovals).

Temperature at center is ~20000K. Note relation between temperature and pressure – pressure needed to prevent collapse (and more upper weight requires more pressure). Note odd state of metallic hydrogen (conducting – semi-free electrons). Core is uncertain (current limit about 5 earth masses – that’s odd).

Note the putative core in Jupiter is about the size of the Earth. The temperature increases inward because the pressure is increasing. Jupiter is almost as big as a non-star can be. More than twice its mass causes the density in the body to go up faster and it actually gets more compact.

The clouds we see are mostly ammonia. Talk about the most common elements: H,He,C,N,O. He is inert. H forms molecules with the others: 0H_2 (water), NH_3 (ammonia), CH_4 (methane). These are among the most common molecules around (along with forms involving C + O or N). Note that there are layers with room temperature water clouds (and only a few atmospheres pressure). We don’t understand the trace constituents that give the clouds color. The temperature keeps increasing toward the interior.

Repeat that convection is bringing heat outward. As the cells spread at the surface, the rapid rotation of the planet brings Coriolis forces to bear (same as generate hurricanes on Earth, but we aren’t going to try to explain this in detail). These end up generating “jet streams” with different directions. How do we decide what the “real” rotation rate is (some winds are faster, some slower, so they look like they go in opposite directions). We use the magnetic field from the interior.

The metallic hydroden is conducting. Jupiter’s field is quite strong.

Jupiter has by far the strongest field. Venus may be too slow a rotator – no field. The magnetic fields trap high energy particles, making “radiation belts”. Astronauts have to stay out of them, and spacecraft near Jupiter have to be specially designed. Particles from Io are trapped in a doughnut or “torus” around Jupiter. Note the off-center fields for Uranus and Neptune.

These auroral pictures are taken in UV light.

We’ve already discussed most of the interesting planetary aspects of Saturn, since it is much like Jupiter. We’ll come back to the rings later.

Featureless in visible light, because clouds are below haze layer of methane (colder than Saturn). Can see a little in UV light (right, false color).

Image on left from HST, on right from AO on ground. Pluto goes around twice while Neptune goes around 3 times, but inclination means they won’t collide.

Triton is a retrograde moon of Neptune (one wonders whether impacts or encounters played a role in that). Triton’s volcanoes are driven by changing solar flux. Note the dark plumes on the surface which mark eruptions (maybe more like geysers).