Exam #2

1. Exam #2 Average: 85.5% Median: 87.8% High: 102%

2. No Office Hours Today Regular Friday office hours in effect. Or contact me for other hours.

3. Press Release Talk Thursday, November 8: Hunter and Zac will talk about: “Astronomers Release Most Complete Ultraviolet-Light Survey of Nearby Galaxies” http://hubblesite.org/news_release/news/2018-27

4. Press Release Talk Thursday, November 8: Michael and Cole will talk about: “Gravitational Waves and the LIGO Instrument”

5. Chapter 11Jovian Planet Systems

6. Jovian Planet Composition • Jupiter and Saturn - mostly H and He gas, and some ice+rock+metal (but still ~5 Earth masses of it!) • Uranus and Neptune - mostly hydrogen compounds: water (H2O), methane (CH4), ammonia (NH3), some H, He, and rock+metal

7. Density Differences • Uranus and Neptune are denser than Saturn because they have less H/He, proportionately. • H/He more spread out at larger distances in solar nebula  less gas for Uranus/Neptune to accrete.

8. Density Differences • But that explanation doesn’t work for Jupiter, as it should be even less dense than Saturn given it has an even larger H/He content.

9. Sizes of Jovian Planets • Adding mass to a Jovian planet compresses the underlying gas layers. • Each additional “pillow” (layer of gas) adds an extra unit of gas, but adds less than one unit to the radius.

10. Sizes of Jovian Planets • Greater compression is why Jupiter is not much larger than Saturn even though it is three times more massive. • Jovian planets with even more mass can be smaller than Jupiter (including brown dwarfs).

11. Rotation and Shape • Jovian planets are not quite spherical because of their rapid rotation  due to centrifugal force. • Jupiter: < 10 hours • Saturn: 10.5 hours • Rotation rates vary with latitude

12. Interiors of Jovian Planets • No solid surface • Layers under high pressure and temperatures • Cores (~3-7 Earth masses) made of hydrogen compounds, metals, and rock • The layers are different for the different planets.

13. What are Jovian planets like on the inside? +helium Galileo probe only flew in 130 km (0.2%) inside Jupiter’s atmosphere before being destroyed. Models suggest cores of Jovian planets have similar composition, but different layer ratios. Lower pressures inside Uranus and Neptune mean no liquid or metallic hydrogen.

14. Inside Jupiter • High pressures inside Jupiter cause phase of hydrogen to change with depth. • Hydrogen acts like a metal at great depths because its electrons move freely.

15. Metallic Hydrogen • Under high enough pressures, hydrogen atoms are pressed so close that their Bohr radii (electron clouds) begin to overlap. • Electrons no longer “belong” to an individual atom, but float freely among the protons. • Same basic properties as traditional metals, but without the rigid lattice structure.

16. Inside Jupiter • Core is thought to be made of rock, metals, and hydrogen compounds. • Core is about same size as Earth but 3-7 times as massive.

17. Jupiter’s Internal Heat • Jupiter radiates twice as much energy as it receives from the Sun (mostly in infrared). • Energy probably comes from slow contraction of interior (releasing potential energy).

18. Internal Heat of Other Planets • Saturn also radiates twice as much energy as it receives from the Sun. • Energy probably comes from differentiation (helium rain). • Neptune emits twice as much energy as it receives, but the source of that energy remains unknown.

19. What is the weather like on Jovian planets?

20. Jupiter’s Atmosphere • Hydrogen compounds in Jupiter form clouds. • Different cloud layers correspond to freezing points of different hydrogen compounds. ammonium hydrosulfide

21. Jupiter’s Colors • Ammonium sulfide clouds (NH4SH) reflect red/brown. • Ammonia, the highest, coldest layer, reflects white.

22. Jupiter’s Bands Each band is a circulation cell set up by convection and the Coriolis effect, just like on Earth.