Lecture II: Gas Giant Planets

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Lecture II Gas Giant Planets

• The Mass-Radius diagram - interiors
• Equations of State and Phase transitions
• Phase separation
• Hot Jupiters

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The Giant Planets
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HD 209458b a Hot Jupiter
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HD 168443b highly eccentric one
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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)
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Mass-RadiusDiagram
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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

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

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The giant planets - interiors

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Phase diagram (hydrogen)
Guillot (2005)
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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)

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Interiors of Giant Planets
Jupiters core mass and mass of heavy elements

For MZ - the heavy elements are mixed in
the H/He envelope
Saumon Guillot (2004)
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Interiors of Giant Planets
Saturns core mass and mass of heavy elements

Saumon Guillot (2004)
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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)

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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
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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

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Interiors of Hot Jupiters

• Core vs. No-Core
• Core - leads to faster contraction at any age
• the case of OGLE-TR-132b gt 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.

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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.

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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)
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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 x0.085 (solar comp., Y0.27),
  Bconst.(0), A1-2 eV (pressure- dependent
  const.),
• therefore T 5,000 - 10,000 K

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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 !
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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
(Y0.234) Saturn (Y0.2).
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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.
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Evolution Models of Exo-planets
Could the very low-density puffy planets be
heated by phase separation ?

Phase separation of other elements Ne, O
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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)
  ?

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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)

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