Lecture II: Gas Giant Planets

1. Lecture II: Gas Giant Planets The Mass-Radius diagram - interiors Equations of State and Phase transitions Phase separation Hot Jupiters

2. The Giant Planets

3. HD 209458b: a Hot Jupiter

4. HD 168443b: highly eccentric one

5. More diversity than expected ?... Some of the Hot Jupiters do not match well models based on Jupiter & Saturn: Charbonneau et al (2006) w Bodenheimer et al.(2003), Laughlin et al. (2005) models; and Burrows et al. (2003 & 2006)

6. Mass-RadiusDiagram

7. Properties of planets & small stars Models: Baraffe et al. four different ages: 0.5, 1, 3, & 5 Gyr Red: Pont et al. (2005) OGLE-TR-122

8. Stellar Mass and Age: Stellar evolution track for 3 metallicities and Helium content: Age = 7 Gyrs Stars evolve from bottom zero-age main sequence Lines of constant stellar radii HD 209458 Our Sun Cody & Sasselov (2002)

9. HAT-P-1b: the ‘lightest’ planet yet RA = 22 h 58 m Dec = +38o 40’ I = 9.6 mag G0 V Ms = 1.12 MO Porb= 4.46 days Mp = 0.53 Mjup

10. HAT-P-1 = ADS 16402B: The HR diagram and evolutionary tracks fits: Bakos et al. (2006)

11. Interiors of Giant Planets • Our own Solar System: Jupiter & Saturn • Constraints: M, R, age, J2, J4, J6 • EOS is complicated: • mixtures of molecules, atoms, and ions; • partially degenerate & partially coupled. • EOS Lab Experiments (on deuterium): • Laser induced - LLNL-NOVA • Gas gun (up to 0.8 Mbar only) • Pulsed currents - Sandia Z-machine • Converging explosively-driven - Russia (up to 1.07 Mbar)

12. The giant planets - interiors

13. Phase diagram (hydrogen): Guillot (2005)

14. Interiors of Giant Planets • New hydrogen EOS Experiment: • Russian Converging explosively-driven system (CS) • Boriskov et al. (2005): • matches Gas gun & Pulsed current (Z-machine) results • deuterium is monatomic above 0.5 Mbar - no phase transition • consistent with Density Functional Theory calculation (Desjarlais)

15. Interiors of Giant Planets Jupiter’s core mass and mass of heavy elements: For MZ - the heavy elements are mixed in the H/He envelope Saumon & Guillot (2004)

16. Interiors of Giant Planets Saturn’s core mass and mass of heavy elements: Saumon & Guillot (2004)

17. Interiors of Giant Planets • Core vs. No-Core: • How well is a core defined? • Saturn: metallic region can mimic ‘core’ in J2 fit (Guillot 1999); • Core dredge-up - 20 MEarth in Jupiter, but MLT convection… ? • Overall Z enrichment: • Jupiter ~ 6x solar • Saturn ~ 5x solar • a high C/O ratio from Cassini ?? (HD 209458b? Seager et al ‘05)

18. Interiors of Hot Jupiters Hot Jupiters could capture high-Z planetesimals if parked so close early… OGLE-TR-56b has: Vorb = 202 km/sec, Vesc = 38 km/sec. DS (2003) w updates

19. Hot Jupiters: Internal heating • Tidal heating • small ones require cores & enrichments larger than those of Jupiter and Saturn (Burrows et al. 2006); • large ones - their low densities are still difficult to explain: • additional sources of heat • high-opacity atmospheres

20. Interiors of Hot Jupiters • Core vs. No-Core: • Core - leads to faster contraction at any age; • the case of OGLE-TR-132b > high-Z and large core needed ? • the star OGLE-TR-132 seems super-metal-rich… (Moutou et al.) • Cores: nature vs. nurture ? - capturing planetesimals. • Evaporation ? - before planet interior becomes degenerate enough - implications for Very Hot Jupiters; • the case of HD 209458b (Vidal-Madjar et al. 2003) ? • Overall Z enrichment: • After the initial ~1 Gyr leads to more contraction.

21. Summary: Hot Jupiters Our gas giants - Jupiter & Saturn: have small cores are enriched in elements heavier than H (and He) The Hot Jupters we know: most need cores & enrichment six or so need tidal heating or a similar heating source… Is the core-accretion model in trouble ? not yet, but we should understand Jupiter and Saturn better.

22. A Problem with Saturn ?... Its current luminosity is ~50% greater than predicted by models that work for Jupiter: Saturn reaches its current Teff (luminosity) in only 2 Gyr ! Fortney & Hubbard (2004)

23. A Problem with Saturn ?… • One idea for resolving the discrepancy - phase separation of neutral He from liquid metallic H(Stevenson & Salpeter 1977): for a saturation number fraction of the solute (He), phase separation will occur when the temperature drops below T : x = exp (B - A/kT) where x=0.085 (solar comp., Y=0.27), B=const.(~0), A~1-2 eV (pressure- dependent const.), therefore T = 5,000 - 10,000 K

24. A Problem with Saturn ?... Phase diagram for H & He: Fortney & Hubbard (2004) Model results: Stevenson (‘75) vs. Pfaffenzeller et al. (‘95) - different sign for dA/dP !

25. A Problem with Saturn ?... New models: Fortney & Hubbard (2004) Model results: The modified Pfaffenzeller et al. (‘95) phase diagram resolves the discrepancy. Good match to observed helium depletions in the atmospheres of Jupiter (Y=0.234) & Saturn (Y~0.2).

26. Evolution Models of Exo-planets: Cooling curves: Fortney & Hubbard (2004) Models: All planets have 10 ME cores & no irradiation. The models with He separation have ~2 x higher luminosities.

27. Evolution Models of Exo-planets: Could the very low-density “puffy” planets be heated by phase separation ? Phase separation of other elements Ne, O

28. Issues: Sizes of extrasolar planets are already precise but beware of biases & systematic errors! Models are based on Jupiter & Saturn Perhaps, Hot & Very Hot Jupiters are more Z enriched: because of history - excessive migration through disk, or because of orbit - manage to capture more planetesimals ? Implications for the core-accretion model: it requires at least ~6 ME for Mcore of Jupiter & Saturn invoke Jupiter core erosion (e.g. Guillot 2005) ?

29. Conclusions Sizes of extrasolar planets are already precise beware of biases & systematic errors Models are based on Jupiter & Saturn Perhaps, Hot & Very Hot Jupiters are more Z enriched: because of history - excessive migration through disk, or because of orbit - manage to capture more planetesimals ? Implications for the core-accretion model: it requires at least ~6 ME for Mcore of Jupiter & Saturn invoke Jupiter core erosion (e.g. Guillot 2005), use the He settling for Saturn (Fortney & Hubbard 2003)