Signatures of Exoplanets HD209458b: a Hot Jupiter Orbiting a Bright Star Sara Seager Carnegie Institution of Washington Image credit: NASA/JPL-Caltech/R. Hurt (SSC)

Signatures of Exoplanets HD209458b: a Hot Jupiter Orbiting a Bright Star Introduction Models Data HD209458b Near Future

Planet sizes are to scale. Separations are not. Characterizing extrasolar planets: very different from solar system planets, yet solar system planets are their local analogues The Solar System

Star J M V E Seager 2003 Hot Jupiters F p /F * = p R p 2 /a 2 F p /F * = T p /T * R p 2 /R * 2 = (R * /2a) 1/2 [f(1-A)] 1/4 Solar System at 10 pc

Transiting planets allow us to move beyond minimum mass and orbital parameters without direct detection. HD209458b. November Lynnette Cook. Venus. Trace Satellite. June Schneider and Pasachoff. Mercury. Trace Satellite. November Transiting Planets

Seager, in preparation Transiting Planets Transit [R p /R * ] 2 ~  Transit radius Emission spectra T p /T * (R p /R * ) 2 ~10 -3  Emitting atmosphere  ~2/3  Temperature and  T Transmission spectra [atm/R * ] 2 ~10 -4  Upper atmosphere  Exosphere ( ) Reflection spectra p[R p /a] 2 ~10 -5  Albedo, phase curve  Scattering atmosphere Before direct detection

Compelling Questions for Hot Jupiter Atmospheres Do their atmospheres have ~ solar composition?  Or are they metal-rich like the solar system planets?  Has atmospheric escape of light gases affected the abundances? Are the atmospheres in chemical equilibrium?  Photoionization and photochemistry? How is the absorbed stellar energy redistributed in the atmosphere?  Hot Jupiters are tidally locked with a permanent day side  And are in a radiation forcing regime unlike any planets in the solar system

Signatures of Exoplanets Introduction Models Data HD209458b Near Future

Hot Jupiter Spectra Teff = K Major absorbers are H 2 O, CO, CH 4, Na, K, H 2 Rayleigh scattering High temperature condensate clouds may be present: MgSiO 3, Fe Scattered light at visible wavelengths Thermal emission at IR wavelengths See also Barman et al. 2001, Sudarsky et al. 2003, Burrows et al. 2005, Fortney et al 2005, Seager et al Seager et al. 2000

Giant Planet Spectra dI(s, , )/ds = -  (s, )I(s, , ) + j(s, , );  (s, ) ~ T,P; T,P ~ I(s, , ); 1D models Governed by opacities “What you put in is what you get out” Seager, in preparation FKSI Danchi et al. 20 pc 0.05AU 0.1 AU 0.5 AU

Clouds Spectra of every solar system body with an atmosphere is affected by clouds For extrasolar planets1D cloud models are being used Cloud particle formation and subsequent growth based on microphysical timescale arguments Cloud models have their own uncertainties Homogenous, globally averaged clouds Marley et al Ackerman & Marley, Cooper et al. 2003; Lunine et al. 2001

Liang, Seager et al. ApJL 2004 Liang et al. ApJL 2003 Photochemistry Jupiter and Saturn have hydrocarbon hazes--mute the albedo and reflection spectrum Hot Jupiters have 10 4 times more UV flux = more hydrocarbons? Much higher hydrocarbon destruction rate  normal bottleneck reaction is fast  less source from CH 4  additional consequence: huge H reservoir from H 2 O Karkoschka Icarus 1994

Large Range of Parameters Forward problem is straightforward despite uncertainties Clouds  Particle size distribution, composition, and shape  Fraction of gas condensed  Vertical extent of cloud Seager et al Opacities Non-equilibrium chemistry Atmospheric circulation of heat redistribution Internal luminosities (mass and age dependent)

Signatures of Exoplanets Introduction Models Data HD209458b Near Future

Seager, in preparation Hot Transiting Planets Orbiting Bright Stars Transit [R p /R * ] 2 ~  Transit radius Emission spectra T p /T * (R p /R * ) 2 ~10 -3  Emitting atmosphere  ~2/3  Temperature and  T Transmission spectra [atm/R * ] 2 ~10 -4  Upper atmosphere  Exosphere ( ) Reflection spectra p[R p /a] 2 ~10 -5  Albedo, phase curve  Scattering atmosphere Pushing the limits of telescope instrumentation

Thermal Emission: Spitzer 24 micron flux  Secondary eclipse  Thermal emission detected at 24  m  Direct measurement of planetary flux  Brightness temperature at 24  m is derived /- 150 K  Deming, Seager, Richardson, Harrington 2005

Richardson, et. al., in prep Thermal Emission: NASA IRTF 2.2  m Constraint Secondary eclipse Spectral peak at 2.2  m due to H 2 O and CO Data from NASA IRTF  R = 1500  Richardson, Deming, Seager 2003; Differential measurement only Upper limit of the band depth on either side of the 2.2 micron peak is 1 x or 200  Jy

Reflected Light: MOST Geometric Albedo Upper Limit Geometric albedo preliminary upper limit is 0.4 Jupiter’s geometric albedo in the MOST bandpass is 0.5 Bond albedo is almost 1.5 x lower than the geometric albedo for the solar system gas giant planets

Transmission Spectra: HST STIS and Keck Probes planetary limb Na (Charbonneau et al. 2002) CO upper limit (Deming et al. 2005)  Consistent with high clouds  Or low Na and CO abundance H Lyman alpha ( Vidal-Madjar et al. 2003)

Signatures of Exoplanets Introduction Models Data HD209458b Near Future

HD209458b: Interpretation I Basic picture is confirmed Thermal emission data  T 24 = /- 150 K  The planet is hot!  Implies heated from external radiation Transmission spectra data  Presence of Na A wide range of models fit the data Seager et al. 2005

HD209458b: Interpretation II Models are required to interpret 24  m data  H 2 O opacities shape spectrum T 24 is not the equilibrium T  T 24 = /- 150 K  A wide range of models match the 24  m flux/T T eq is a global parameter of model  Energy balance, albedo, circulation regime  E.g. T eq = 1700 K implies that A B is low and absorbed energy is reradiated on the day side only

HD209458b: Interpretation II Models are required to interpret 24  m data  H 2 O opacities shape spectrum T 24 is not the equilibrium T  T 24 = /- 150 K  A wide range of models match the 24  m flux/T T eq is a global parameter of model  Energy balance, albedo, circulation regime  E.g. T eq = 1700 K implies that A B is low and absorbed energy is reradiated on the day side only

HD209458b: Interpretation III Models with strong H 2 O absorption ruled out Hottest models are ruled out  Isothermal hot model is ruled out by T 24 = /- 150 K  Steep T gradient hot model would fit T 24 but is ruled out by 2.2  m constraint Coldest models are ruled out  High albedo required--very unusual  Cold isothermal model required to fit T 24 --doesn’t cross cloud condensation curves  Confirmed by MOST

HD209458b: Interpretation III Beyond the “standard models”  Low H 2 O abundance would fit the data  C/O > 1 is one way to reach this  See Kuchner and Seager 2005

HD209458b C/O > 1

HD209458b Interpretation Summary Data for day side  Spitzer 24 microns  IRTF 2.2 micron constraint  MOST albedo upper limit A wide range of models fit the data  Confirms our basic understanding of hot Jupiter atmospheric physics Some models can be ruled out  Hot end of temperature range  Cold end of temperature range  Any model with very strong H2O absorption at 2.2 microns Non standard models  C/O > 1 could fit the data

Signatures of Exoplanets Introduction Models Data HD209458b Near Future

Near Future Data from Seager et al. 2005

Signatures of Exoplanets HD209458b: a Hot Jupiter Orbiting a Bright Star Transiting planet atmospheres can be characterized without direct detection Models are maturing, ideas beyond the solar abundance, chemical equilibrium models are being considered A growing data set for HD209458b

Extrasolar Planet Discovery Timeline Past 1992pulsar planet 09/1995 Doppler extrasolar planet discoveries take off 11/1999 extrasolar planet transit 11/2001 extrasolar planet atmosphere 1/2003 planet discovered with transit method 4/2004 planet discovered with microlensing method Present 2005 transit planet discoveries take off 2005 transit planet day side temperature 2005 hot Jupiter albedo Future 2008 hundreds of hot Jupiter illumination phase curves 2011 Frequency of Earths and super earths 2016 First directly detected Earth-like planet 2025 Unthinkable diversity of planetary systems!

HD209458b Exosphere Detection 15% deep Lyman alpha transit 4.3R J Requires exospheric temperature ~ 10,000K! High exospheric temperatures on solar system giant planets are not well understood (order of magnitude) XUV heating (Lammer 2003) a first step Upper atmospheric T, atmospheric expansion, and mass loss are coupled If significant mass loss, how does it affect the atmospheric signature? No UV followup measurements possible

Tidally locked hot Jupiters; but simple day/night picture is naive Spectral signatures depend on T and T gradient Chemical species will be transported Not yet incorporated into radiative transfer models Showman & Guillot A&A 2002 Cho et al. ApJL 2003 Tracer pv Temp Atmospheric Circulation