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On the front of exoplanet modelling: ! Interior structures, atmospheres and evolution

I. Baraffe University of Exeter


The building blocks for modelling (exo)planets
Atmospheres (1D static, irradiated/non irradiated)
Cambridge; Exeter; Leicester; St Andrews; Hertfordshire; UCL, etc...

Atmospheres (d

Tamics) ext yn

Heating processes; Ohmic dissipation; Mixing Exeter; Queen Mary; Open University; Oxford

H/He envelope Rocky/icy core
«Ices»(H20, CH4, NH3), silicates (MgSiO4, MgSiO3,...), Iron (Fe) Earth-like:internal dynamics (plate tectonics,volcanism, melting)

Equation of State for H/He/Z Evolutionary models Tidal processes Cambridge DAMPT; Exeter; Open University

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Current status of interior structures:
! Still large uncertainties on interior structure models of our own giant planets (EOS, amount of heavy elements, size of core) ! large uncertainties on the determination of exoplanet internal compositions from observed mass-radius

Progress are coming with improved EOS of H/He and heavy materials (water, silicates, etc) at high pressure and high temperature
!

§ Ongoing and future high-pressure experiments (Livermore, Sandia in the US;
Laser Megajoule in France)
(Loubeyre et al.; Knudson et al.; etc..)

!

§ First principle methods (quantum molecular dynamics, DFT, path integral)
(Chabrier et al; French et al., Mazevet et al. , Millitzer et al.; Nettelmann et al.; etc...)

!

First applications to our Solar System Planets


The standard picture:
· · ·

Internal structure of Jupiter and Saturn based on the "three-layer" picture
Equation of state of Saumon-Chabrier for H/He (semi-analytical)
Equations of state for metals from ANEOS (Sandia) /SESAME (Los Alamos)
(relevant regime P ~ 1 Mbar - 100 Mbar: interpolated between experiments
and asymptotic limits in the very high density, fully ionised limit)

Jupiter: - Mcore = 0 - 11 M




- Total Z = 8-39 M

Possible solution with a very small core suggested for Jupiter (Saumon & Guillot 2004)

Note: fully adiabatic layers (efficient convection)
Guillot 1999


More recent picture:
Based on improved EOS (first-principle) and two- or three-layers

based on a 2-layer model: core of rock/H2O and isentropic mantle of H/He Find a core for Jupiter of Mcore = 14-18 M (Militzer et al. 2008)
! !

Small core hypothesis for Jupiter challenged by those recent calculations

Strong disagreement with another study also based on ab initio EOS calculations for H, He and H2O (Nettelmann et al. 2008) based on a 3-layer model: core of rocks/ice + inner isentropic envelop (Metallic H, He, Zmet) + outer isentropic envelope (molecular H2, He, Zmol)
!

Find a core for Jupiter of M

core

= 0-7 M

·

Other improvement: cooling models for our four Giant Planets Fortney & Nettelmann 2010; Fortney et al. 2011 (self-consistent atmosphere and structure models)
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Adiabatic interior (fully convective): revisiting the standard picture?

·

Double-diffusive convection in Jupiter and Saturn? (Leconte & Chabrier 2012, 2013 Nature Geosc.) Non conventional interior model for J and S core + inhomogeneous, "semiconvective" envelope Reproduce the gravitational moments J2 and J4 · Jupiter: Mcore= 0 - 0.5 M Ztot = 13% - 20% (previous: Ztot = 2.5% - 12%)

Text

!

· Saturne: Mcore= 12 - 21 M
Ztot = 28% - 44% (previous: Ztot = 13% - 29%)
!

Layered convection could explain Saturn's luminosity anomaly
(anomalously high intrinsic flux that adiabatic models cannot reproduce)

Inhomogeneous models for Jupiter and Saturn are significantly more enriched in heavy material (30%-60% more) than previously thought 6


Uranus & Neptune:
!

Recent models by Nettelmann et al. 2013: constraint the metallicity of the "water-rich" inner envelope with Z2 and the H-He rich outer envelope with Z1
(water EOS of French et al. (2009) based on Quantum Molecular Dynamics simulations) 1.2
0,6 0.7

Z

- Improved gravity field data (long term observations of planet's satellite motions)
- Modified shape and rotational periods compared to Voyager data

0.3 0,5 0,4
1

Neptune
0.1

0,3 0,2

0.05

0.01 0,1

Uranus
0.15 0.12

0

0,8

0,9

Z

2

Nettelmann et al. 2013

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Knowledge of Solar System planets applied to understand the huge diversity of planetary structures from the massradius relationship of known planets
Transiting exoplanets Solar System

Baraffe, Chabrier, Fortney, Sotin, PPVI 2013
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The problem of inflated planets
Significant fraction of exoplanets with abnormally large radius

!

Missing physics in planetary
interior models?




Z¤

Summary in Baraffe et al. PPVI 2014


a) Incident stellar flux driven mechanism ! ! · - Atmospheric circulation: (Showman & Guillot 2002)
! -----> downward transport of kinetic energy down to the internal adiabat Heats the planet and slows down the contraction
! · Ohmic dissipation: (Batygin & Stevenson 2010; Perna et al. 2010)
! -----> Atmospheric winds produce currents penetrating in the interior
Ohmic heating in the interior = J2/()
! ! b) Tidal mechanisms (Bodenheimer et al. 2001)
!




Difficult to explain with tidal effects alone properties of several inflated planets (HD209458b, WASP-12b, etc..) (Leconte et al. 2010)



! c) Delayed contraction ! Enhanced atmospheric opacities: (Burrows et al. 2007)
Double diffusive convection (semiconvection): (Chabrier & Baraffe 2007)
!


Future missions in the Solar System to improve planetary models
·

Juno (2016): for Jupiter! - Mapping accurately gravitational moments up to J12! constraint on the density distribution and internal structure! constraints on differential or solid body rotation of the outer layers! - Mapping of the magnetic field!

! !

- Spectroscopy of thermal emission down to 100 bars! measure of H2O and NH3 mixing ratios
!

Final stages of Cassini (2017): for Saturn! - Precision mapping of gravitational moments (up to J10) and magnetic fields! - Possible in situ sampling of atmospheric mixing ratios! (heroic death with the craft manoeuvred down in the atmosphere) ! · Seismology: ! - First detection of Jupiter 's oscillations by SYMPA (Gaulme et al. 2011)! - Detection by Cassini of spiral structures in Saturn's ring which could be due to perturbations from Saturn's free oscilations ! seismology studies should be pursued!
·


The future: (some future theoretical developments)

· Improved EOS of H/He and heavy materials (water, silicates, etc) at high pressure and high temperature
Progress are coming with experiments and ab-initio calculations!

! !

· Development of numerical simulations to confirm the existence of layered convection in planetary interiors (Rosenblum et al. 2011; Mirouh et al. 2012)



!

Planets are not necessarily fully adiabatic and homogeneous
Important impact on our own giant planets!


· Development of dynamical atmospheric models (heating/cooling + circulation + radiative transfer + magnetic drag)




Solution for abnormally large radii of close-in planets?
Effect on spectral signatures


Some questions Interior models: how can we improve the problem of degeneracy of internal composition to (i) get the best from coming observations (NGTS, PLATO, CHEOPS, TESS, etc...)? (ii) make the link with formation models?
·

!
·

Atmosphere: how can we test retrieval methods? can we use BD as testbeds?

!

GCM: real strength in the UK (Met office UM, Exomol, cloud/ chemistry expertise, fluid dynamics expertise) How ideal can models be to answer questions? How far can we go in complexity to answer questions? (coupling dynamics +RT + chemistry + clouds is just unrealistic now)
·

! !