characterization of extrasolar planets
TRANSCRIPT
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Characterization ofExtrasolar Planets
Mark MarleyNASA Ames Research Center
Characterizing Planets
â˘Why do it?
â˘How to measure M and R?
â˘Evolution and spectral fitting
â˘Atmospheric modeling and spectra
â˘Conclusions
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Why Characterize GiantPlanets?
Giant Planets are notInteresting
â˘Radial velocity & SIM will determine masses and orbits
â˘Giants are not interesting for astrobiology
â˘Giant planet science provides no heritage for terrestrialplanet characterization and is a ânicheâ field
â˘Why build specialized instruments?
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Giant Planets are Interesting
â˘Radial velocity & SIM will determine masses andorbits: Planets are more than masses on springs and wellcharacterized planets are fiducials for more distant objects
â˘Giants are not interesting for astrobiology: theyprovide a record of stellar system formation &perhaps volatile transport
â˘Giant planet science provides no heritage forterrestrial planet characterization: provide end to endexperience of planet characterization, heritage forbigger efforts
Characterizationâ˘Mass - Images can resolve
sin i; RV less useful forsome groundbaseddetections (longer P, youngstars)
â˘Radius - Scattered lightalone does not tightlyconstrain radius sincealbedo uncertain - R2a
Need independent M & R measures
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Fortney et al. (2005)
Kuchner (2005)
Fortney et al. (2007)
Planet radii yieldbulk composition
Gl 436b
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How to Constrain M & R?
Radius: IR + Visible
Mid-IR Visible
R
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M = 1 MJ; age = 1 - 3 Gyr
â δL/L = 60%also will dependon composition
MJ
Constraining R
Mid-IR Visible
R
easily 30% or more
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Kuchner (2005)
Mass from Evolution
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Burrows et al. 1997
Tef
f (K)
log Age (Gyr)
3500
500
A case study: Gl 570D (T8) - Saumon et al. (2003)
Primary (Gl 570A):
d = 5.91Âą0.05pc(Perryman et al. 1997)
[Fe/H] = 0.00Âą0.12(Feltzing & Gustafsson 1998)
Age = 2â5 Gyr(Saumon et al. 2000)
Spectroscopy:Optical (Burgasser)Near IR (Leggett)Mâ (Geballe)Mid IRS (Spitzer/IRS Dim Suns team)
~70% of SED has been sampled
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1 Gyr
2
5
10
0.005
0.01
0.02
0.03
0.04
0.05
0.060.07Mo
Luminosity constrains Teff & g
1) bolometric correctionfrom model spectra
2) Evolution
3) Teff(g) follows from
Teff=800 K log g=5.09 Lbol/Lo=2.99X10-6
The resulting spectrum (not normalized!)
Îť (Âľm)
NH3
Wavelength (Âľm)
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Evolution Works,But....
â˘Assumes companion composition = primary
â˘Substantial wavelength coverage to measure Lbol
â˘Gyr age primary
â˘Radii of mature brown dwarfs understood
â˘More challenging at young ages & lower masses
â˘Spectra most definitive
Metallicity1/2 to 2 solar
Gravity15 - 75MJ
Teff
600 to 800 K
Wavelength (Âľm)
750 K, log g = 5.0, m/H = 0
R = 400Legg
ett
et a
l. (2
007)
1.0 2.4
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Wavelength (Âľm)1.0 2.4
Legg
ett
et a
l. (2
007)
HD 3651B
Results from good spectral coverage
Radius (arcsec)
H b
and
Con
tras
t
10-4
10-6
10-8
10-10
0.01 0.10 1.00
Courtesy B. Macintosh & J. Graham
Real Data More Like This
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2M1207 Companion
⢠Companion to ~M8 brown dwarf inTW Hydrae (age ~ 8 Myr)
⢠red J-K implies late L, Teff
~ 1250 K
⢠Models give M = 5 ¹ 2 MJup
Chauvin et al. (2004)
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Burrows et al. 1997
Tef
f (K)
log Age (Gyr)
3500
500
Believable at young ages?
Stassun et al. (2006)
M1 54 Âą 5 MJ
M2 34 Âą 3 MJ
R1 6.5 RJ
R2 5.0 RJ
2M0535eclipsing binary in Orion
age âfew 106 yearsâ
Burrows et al. (2001)
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Young Brown Dwarfs
â˘Evolutionary models passed some tests
â˘But...early evolution is highly sensitive toinitial conditions
â˘Need more observational tests
Planets remember their formationmechanism, which is likely different from low
mass companions.
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Core Accreted Planets:
â˘Smaller
â˘Cooler
â˘Fainter
R
Teff
L
time (years) Marley et al. (2007)
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Marley et al. (2006)
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Marley et al. (2006)
Core Accreted Giantsâ˘Model luminosity depends on treatment of
accretion shock
â˘Many uncertainties (geometry, energy partioning,disk) remain
â˘Baseline model suggests young Jupiters aremuch fainter than expected
â˘Discrepancy increases with mass
⢠See Marley et al. (2007)
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Low Mass Companions canbe Distinguished from
Planetsâ˘Formation clues are detectable
â˘Composition (different from primary)
â˘Radius
â˘Luminosity
Radius (arcsec)
H b
and
Con
tras
t
10-4
10-6
10-8
10-10
0.01 0.10 1.00
Courtesy B. Macintosh & J. Graham
True Jupiters
Low Mass Companions
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Characterizationâ˘Mass - spectra
â˘Radius - spectra
â˘Albedo
â˘Effective temperature - spectra
â˘Equilibrium temperature
⢠Internal luminosity
Characterizationâ˘Mass
â˘Radius
â˘Albedo
â˘Effective temperature
â˘Equilibrium temperature
⢠Internal luminosity
â˘Atmospheric Composition
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Owen et al. (1999)
signature of planethood?
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But...
Requiring compostioninformation turns most ofthe âKnown Exoplanetsâinto âKnown Exoplanet
Candidatesâ
Known Exoplanets:HD149026b
Gl 436b
Models
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Appleby & Hogan (1984)
McKay et al. (1989)
Marley & McKay (1999)
⢠Composition
⢠Chemistry
⢠Opacities
⢠Condensates
⢠+ Dynamics
⢠Thermal Structure & Spectrum
Metallicity, C/O, ...
Sedimentation
High T CH4
Cloud Physics
Circulation, f
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EGP Characterization RequiresSpectra
Band depthsare crucial
Fortney & Marley
1440 K
870 K
375 K 115 K
135 K
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Jupiter Cloudless Hot Jupiter
Lodders (2005)
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Marley et al. (1999)
CH4
H2O Na, K
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Lessons from Brown Dwarfs
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Sudarsky et al. (2003); Burrows (2005)
Photochemistry
⢠25x higher UV flux
â˘H, C, O, N, S, P chemistry
â˘Many pathways to hazes
⢠But...Liang et al. (2004) find nohazes in hot Jupiters
Jupiter at 1 AU
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Haze Production
⢠CH4 + UV
â˘C2H2 C2H6
â˘C6H6 C3H8
â˘Soot parafin
â˘New Paradigm? Old School
Substantially alter spectra andcolors of canonical haze-freemodels
Dynamics & ChemicalEqulibrium
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Noll et al. (1997)
Non-equilibrium CO⢠Convection or eddy mixing can
transport CO⢠Strong bond allows dynamical Ď
<< chemical equilibrium Ď⢠Excess CO observed in Jupiter
(Prinn & Barshay 1977)⢠Predicted (Fegley & Lodders
1996) and observed (Noll et al.1997) in Gl229B⢠Can CO attenuate EGP 5-¾m
excess? Relevant for JWSTplanet search
CO and Vertical Mixingâ˘Models fit observed J,H, K, Lâ reasonablywell
⢠T dwarfs are generallyfainter at M thanexpected
⢠Brightness at M bandadvertised to easeEGP direct detection:â...we believe that thisband is a universaldiagnostic for browndwarfs and jovianplanets.â Marley et al.1996
Burrows et al. 1997
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H2O
CH4CO
1000 K; 1 bar
Methane arrives late at L, CO hangs in longer
Saumon et al. 2003
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Saumon et al. 2003
Leggett et al. (2007)
M4.5M3.6
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M band Less Favorable forPlanet Searches
â˘Up to 40% dimmer than previously expected
â˘Full phase space of mixing, chemistry not yetexplored
â˘Clouds also major impact
â˘Lâ may be more favorable (lower background,less affected by mixing)
At Low Spectral Resolution
â˘Clouds trump
â˘Hazes are a concern
â˘Metallicity
â˘C/O ratio
â˘Non-equilibrium chemistry influences searchband (Lâ vs. M)
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Conclusionsâ˘Modeling issues are well understood
â˘Mass and Radius are just starting points
â˘For most objects, composition should bemajor goal of characterization
â˘Condensates can cloud our vision
â˘True characterization is challenging, butrewarding