Signatures of Exoplanets HD209458b: a Hot Jupiter Orbiting a Bright Star

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)


IntroductionModelsDataHD209458bNear 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

VE

Seager 2003

Hot Jupiters

Fp/F* = p Rp2/a2

Fp/F* = Tp/T* Rp2/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

1999. Lynnette Cook.

Venus. Trace Satellite. June 8 2004.Schneider and Pasachoff.

Mercury. Trace Satellite. November 1999.

Transiting Planets

Seager, in preparation

Transiting Planets

Transit [Rp/R*]2 ~ 10-2

Transit radius

Emission spectra Tp/T*(Rp/R*)2 ~10-3

Emitting atmosphere ~2/3 Temperature and T

Transmission spectra [atm/R*]2 ~10-4

Upper atmosphere Exosphere (0.05-0.15)

Reflection spectra p[Rp/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


Hot Jupiter Spectra

Teff = 900 - 1700 K Major absorbers are H2O, CO,

CH4, Na, K, H2 Rayleigh scattering

High temperature condensate clouds may be present: MgSiO3, 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. 2005

Seager et al. 2000

Giant PlanetSpectra

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 preparationFKSI Danchi et al.

20 pc

0.05AU0.1 AU0.5 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. 1999

Ackerman & Marley, Cooper et al. 2003; Lunine et al. 2001

Liang, Seager et al. ApJL 2004Liang et al. ApJL 2003

Photochemistry

Jupiter and Saturn have hydrocarbon hazes--mute the albedo and reflection spectrum Hot Jupiters have 104 times more UV flux = more hydrocarbons? Much higher hydrocarbon destruction rate

normal bottleneck reaction is fast less source from CH4

additional consequence: huge H reservoir from H2O

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. 2000

Opacities Non-equilibrium chemistry Atmospheric circulation of heat

redistribution Internal luminosities (mass and age

dependent)



Seager, in preparation

Hot Transiting PlanetsOrbiting Bright Stars

Transit [Rp/R*]2 ~ 10-2

Transit radius

Emission spectra Tp/T*(Rp/R*)2 ~10-3

Emitting atmosphere ~2/3 Temperature and T

Transmission spectra [atm/R*]2 ~10-4

Upper atmosphere Exosphere (0.05-0.15)

Reflection spectra p[Rp/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 1130 +/- 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 H2O 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 10-4 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)



HD209458b: Interpretation I

Basic picture is confirmed Thermal emission data

T24 = 1130 +/- 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

H2O opacities shape spectrum

T24 is not the equilibrium T T24 = 1130 +/- 150 K A wide range of models match the

24 m flux/T

Teq is a global parameter of model Energy balance, albedo,

circulation regime E.g. Teq = 1700 K implies that AB is

low and absorbed energy is reradiated on the day side only

HD209458b: Interpretation II

Models are required to interpret 24 m data

H2O opacities shape spectrum

T24 is not the equilibrium T T24 = 1130 +/- 150 K A wide range of models match the

24 m flux/T

Teq is a global parameter of model Energy balance, albedo,

circulation regime E.g. Teq = 1700 K implies that AB is

low and absorbed energy is reradiated on the day side only

( ) 4/12/1** )]1([2/ AfDRTTeq −=

HD209458b: Interpretation III Models with strong H2O

absorption ruled out Hottest models are ruled out

Isothermal hot model is ruled out by T24 = 1130 +/- 150 K

Steep T gradient hot model would fit T24 but is ruled out by 2.2m constraint

Coldest models are ruled out High albedo required--very

unusual Cold isothermal model required to

fit T24--doesn’t cross cloud condensation curves

Confirmed by MOST

HD209458b: Interpretation III

Beyond the “standard models” Low H2O 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



Near Future Data

from Seager et al. 2005


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 TimelinePast• 1992 pulsar 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 albedoFuture• 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 4.3RJ

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 pvTemp

Atmospheric Circulation

Documents

Signatures of Exoplanets HD209458b: a Hot Jupiter Orbiting a Bright Star