Towards a Physical Characterization of Extrasolar Planets Sara

Towards a Physical Characterization of Extrasolar Planets Sara Seager Carnegie Institution of Washington Image credit: NASA/JPL-Caltech/R. Hurt (SSC)

Towards a Physical Characterization of Extrasolar Planets Transiting Planets Models Data HD 209458 b Near Future Earths

The Solar System 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

Known Extrasolar Planets (As of 24 MAY 2005) Based on data compiled by J. Schneider

Direct Detection Challenge n n Nearby M dwarf star with brown dwarf companion Jupiter would be 10 x closer in ¨ 1 million times fainter ¨ Gliese 229 and 229 B - Hubble Space Telescope (Kulkarni, Golimowski, NASA)

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

Geometric Transit Probability P ~ (R*/a) P(0. 05 AU) = 10% P(1 AU) = 0. 5% P(5 AU) = 0. 1 % a 1 radial velocity planet is known to transit its star Zone where transit can be seen from

Transiting Planets Venus. Trace Satellite. June 8 2004. Schneider and Pasachoff. Mercury. Trace Satellite. November 1999. HD 209458 b. November 1999. Lynnette Cook. Transiting planets allow us to move beyond minimum mass and orbital parameters without direct detection.

Planet Transit Surveys n n n Survey thousands of stars simultaneously Measure drop in starlight due to transiting planet Huge number of false positives Over 20 groups running planet transit surveys Require radial velocity followup to determine mass Two OGLE transiting planets. Six short-period planets successfully discovered

Planet Transit Surveys n n n Survey thousands of stars simultaneously Measure drop in starlight due to transiting planet Huge number of false positives Over 20 groups running planet transit surveys Require radial velocity followup to determine mass Two OGLE transiting planets. Brown et al. Ap. J 2001 Six short-period planets successfully discovered

Why Transiting Planets? n Planetary bulk composition H-He gas giant? ¨ Super Earth? ¨ Water world? ¨ Rocky planet? ¨ n Evolutionary history HD 209458 b -- too big! ¨ HD 149026 -- too small! ¨ Courtesy Jeremy Richardson

Transiting Planets n Transit [Rp/R*]2 ~ 10 -2 ¨ n Transit radius Emission spectra Tp/T*(Rp/R*)2 ~10 -3 Emitting atmosphere ~2/3 ¨ Temperature and T ¨ n Transmission spectra [atm/R*]2 ~10 -4 Upper atmosphere ¨ Exosphere (0. 05 -0. 15) ¨ n Reflection spectra p[Rp/a]2~10 -5 Albedo, phase curve ¨ Scattering atmosphere ¨ Polarization ¨ Before direct detection Seager, in preparation

Compelling Questions for Hot Jupiter Atmospheres n 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? ¨ n Are the atmospheres in chemical equilibrium? ¨ n 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 ¨

Towards a Physical Characterization of Exoplanets Transiting Planets Models Data HD 209458 b Near Future Earths

Giant Planet Spectra 20 pc d. I(s, , )/ds = - (s, )I(s, , ) + j(s, , ); (s, ) ~ T, P; T, P ~ I(s, , ); n n 1 D models n Governed by opacities n “What you put in is what you get out” 0. 05 AU 0. 1 AU 0. 5 AU Seager, in preparation FKSI Danchi et al.

Hot Jupiter Spectra n n n Scattered light at visible wavelengths Thermal emission at IR wavelengths Teff = 900 - 1700 K H 2 O, CH 4, Na, K, H 2 Rayleigh scattering High T condensate clouds? Mg. Si. O 3, Fe? Seager et al. 2000 See also Barman et al. 2001, Sudarsky et al. 2003, Burrows et al. 2005, Fortney et al 2005, Seager et al. 2005

Clouds n n n Spectra of every solar system body with an atmosphere is affected by clouds For extrasolar planets 1 D 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

Photochemistry Karkoschka Icarus 1994 n n n 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 CH 4 additional consequence: huge H reservoir from H 2 O Liang, Seager et al. Ap. JL 2004 Liang et al. Ap. JL 2003

Large Range of Parameters Seager et al. 2000 n n n Forward problem is straightforward despite uncertainties Clouds ¨ ¨ ¨ Particle size distribution, composition, and shape Fraction of gas condensed Vertical extent of cloud n n n Opacities Non-equilibrium chemistry Atmospheric circulation of heat redistribution Internal luminosities (mass and age dependent)

Towards a Physical Characterization of Exoplanets Transiting Planets Models Data HD 209458 b Near Future Earths

Observations of HD 209458 b Primary Eclipse Na (Charbonneau et al. 2001) n Lyman-alpha (Vidal-Madjar et al. 2003) n C and O* (Vidal-Madjar et al. 2004) n CO upper limit (Deming et al. 2005 a) n Secondary Eclipse n n n Thermal emission 24 m (Deming et al. 2005) Tr. ES-1 at 4. 5 and 8 m (Charbonneau et al 2005) CH 4 upper limit 3. 6 m (Richardson et al. 2003 a) H 2 O upper limit 2. 2 m (Richardson et al. 2003 b) MOST albedo upper limit (Rowe et al. 2005)

Thermal Emission § Detected from two transiting planets during secondary eclipse § Brightness T § HD 209458 b 24 m § 1130 +/- 150 K § Tr. ES-1 4. 5 and 8 m § 1010 +/- 60 K/1230 +/- 110 K § Opens the door for many more measurements Deming, Seager, Richardson, Harrington 2005 Charbonneau et al. 2005

Thermal Emission: NASA IRTF 2. 2 m Constraint n n n Secondary eclipse Spectral peak at 2. 2 m due to H 2 O and CO Data from NASA IRTF ¨ ¨ n n 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 Richardson, et. al. , in prep

Transmission Spectra: HST STIS and Keck n n n 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 n H Lyman alpha (Vidal-Madjar et al. 2003)

Transmission Spectra: HD 209458 b Exosphere n n n n 15% deep Lyman alpha transit 4. 3 RJ Requires exospheric T ~ 10, 000 K! High exospheric T on solar system giant planets are not well understood (order of magnitude) EUV heating Upper atmospheric T, atmospheric expansion, and mass loss are coupled Escape rates are high but atmosphere is stable over billions of years No UV followup possible

Secondary Eclipse: Albedo Upper Limit from MOST n n n Microvariability and Oscillations of STars Space-based photometer for stellar seismology and exoplanet studies ppm photometry “Suitcase” in space 54 kg, 60 x 30 ¨ 15 -cm telescope ¨ Single broadband filter ¨ 380 ≤ λ ≤ 750 nm ¨ n Launch 30 June 2003 ¨ n Russian Rockot = old ICBM Cost ¨ Can$10 M US$7 M Euro$6 M PI Jaymie Matthews UBC

Secondary Eclipse: Albedo Upper Limit from MOST n n n Microvariability and Oscillations of STars Space-based photometer for stellar seismology and exoplanet studies - ppm photometry “Suitcase” in space ¨ ¨ n Launch 30 June 2003 ¨ n 54 kg, 60 x 30 15 -cm telescope Single broadband filter 380 ≤ λ ≤ 750 nm Russian Rockot = old ICBM Cost ¨ Can$10 M US$7 M Euro$6 M PI Jaymie Matthews UBC

MOST Albedo Upper Limit Rowe et al. 2005 n n HD 209458 b albedo < 0. 25 (1 ) in the MOST bandpass Jupiter’s albedo is 0. 5 HD 209458 b is dark! MOST will reach 0. 13 in current observing campaign

Towards a Physical Characterization of Exoplanets Transiting Planets Models Data HD 209458 b Near Future Earths

HD 209458 b: Interpretation I n n Basic picture is confirmed Thermal emission data ¨ T 24 = 1130 +/- 150 K The planet is hot! ¨ Implies heated from external radiation ¨ n Transmission spectra data ¨ n Presence of Na A wide range of models fit the data Seager et al. 2005

HD 209458 b: Interpretation II n Models are required to interpret 24 m data ¨ n H 2 O opacities shape spectrum T 24 is not the equilibrium T T 24 = 1130 +/- 150 K ¨ A wide range of models match the 24 m flux/T ¨ n 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 ¨

HD 209458 b: Interpretation II n Models are required to interpret 24 m data ¨ n H 2 O opacities shape spectrum T 24 is not the equilibrium T T 24 = 1130 +/- 150 K ¨ A wide range of models match the 24 m flux/T ¨ n 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 ¨

HD 209458 b: Interpretation III n n Models with strong H 2 O absorption ruled out Hottest models are ruled out Isothermal hot model is ruled out by T 24 = 1130 +/- 150 K ¨ Steep T gradient hot model would fit T 24 but is ruled out by 2. 2 m constraint ¨ n 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 ¨

HD 209458 b: Interpretation III n 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 ¨ n Solar System giant planets have 3 x solar metallicity ¨ Jupiter may have C/O >~ 1, but spectra look similar to C/O=0. 5

HD 209458 b C/O > 1

HD 209458 b Interpretation Summary n Data for day side Spitzer 24 microns ¨ IRTF 2. 2 micron constraint ¨ MOST albedo upper limit ¨ n A wide range of models fit the data ¨ n 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 H 2 O absorption at 2. 2 microns ¨ n Non standard models ¨ C/O > 1 could fit the data

Towards a Physical Characterization of Exoplanets Transiting Planets Models Data HD 209458 b Near Future Earths

Hot Transiting Planets Orbiting Bright Stars n Transit [Rp/R*]2 ~ 10 -2 ¨ n Transit radius Emission spectra Tp/T*(Rp/R*)2 ~10 -3 Emitting atmosphere ~2/3 ¨ Temperature and T ¨ n Transmission spectra [atm/R*]2 ~10 -4 Upper atmosphere ¨ Exosphere (0. 05 -0. 15) ¨ n Reflection spectra p[Rp/a]2~10 -5 Albedo, phase curve ¨ Scattering atmosphere ¨ Pushing the limits of telescope instrumentation Seager, in preparation

Near Future Data from Seager et al. 2005

Near Future Data n n New transiting planets orbiting bright stars HD 209458 b Spitzer thermal emission 3. 6, 4. 5, 8, 10 microns ¨ HST/STIS primary transit ¨ MOST albedo limit ¨ HST/NICMOS: H 2 O ¨ n Spitzer 3 transiting planets orbiting bright stars ¨ 6 non-transiting planets ¨ n SOFIA, Kepler, JWST Tracer Cho et al. Ap. JL 2003 Temp pv

Hot Super Earths n New Super Earths M=7. 5 ME, P=1. 9 d, Rivera et al. 2005 ¨ Msini =14 ME, P=9. 5 d, Santos et al. 2004 ¨ M=18 ME, P=2. 8 d, 4 -planet system, Mc. Arthur et al. 2004 ¨ Msini=21 ME, P=2. 6 d, M star, Butler et al. 2004 Solar System planet masses ¨ n Uranus: 17. 2 ME ¨ Neptune: 14. 6 ME ¨ Jupiter: 318 ME ¨ Saturn 95 ME An Artist's depiction of the new planet orbiting Gliese 436. Credit: NASA/JPL. ¨ n What is the nature of these planets? ? Credit: NASA/JPL.

Towards a Physical Characterization of Exoplanets Transiting Planets Models Data HD 209458 b Near Future Earths

Are We Alone? Are there Earthlike planets? Are they common? Do they harbor

Terrestrial Planets Evolution of the planetary atmosphere is determined by many factors: • atmospheric escape But, Venus and Earth • gas-surface reactions look the same to • spectral energy distribution of host star Kepler and SIM • geologic activity • initial volatile inventory • active biology • atmospheric circulation will drive climate

NASA’s Terrestrial Planet Finder • Find and characterize Earth-like planets around nearby stars • Need to null out parent star by 106 to 1010 • Look for biomarker gases • Launch date: • 2014 TPF-C • 2019 TPF-I mid-IR spectra

Earth as an Extrasolar Planet Woolf , Smith, Traub, Jucks, Ap. J, 2002 Modeling 1 D Earth spectra is made easier by the right input data!

Earth as an Extrasolar Planet High contrast between land ocean causes changes in flux • rotational period • weather • presence of oceans • reconstruct map? Ford, Seager, & Turner, Nature 2001

Vegetation as a Surface Biomarker S. Seager Institute for Advanced Study, Princeton, July 2002

Vegetation as a Surface Biomarker S. Seager

Surface Biosignature n n n Chlorophyll causes strong absorption blueward of 0. 7 m Light scattering in air gaps between waterfilled plant cells causes strong red reflectance Plants absorb energy at short wavelengths for photosynthesis; reflect and transmit radiation at long wavelengths for thermal balance Reflection favored over transmission? CO 2 more accessible to plants with airgaps Photosynthetic plants cause a global spectral signature even though Earth is not completely plant covered Clark 1993; Seager et al. 2004

Earth as an Extrasolar Planet Woolf , Smith, Traub, Jucks, Ap. J, 2002 Modeling 1 D Earth spectra is made easier by the right input data!

Beyond Earth Kristine Bryan Pangea: 225 million years ago n Paleo. Earth ¨ ¨ Large amount of CH 4? Snowball Earth Pangea Early faint sun paradox n Sun was 30% cooler 4 billion years ago ¨ n CH 4? NH 3? CO 2? Varying orbital and physical planet parameters ¨ ¨ Rotation rates, obliquities, eccentricities Surface temperatures? Cloud cover fractions and patterns? Spectral signatures? Cho and Seager in prep

Towards a Physical Characterization of Extrasolar Planets 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 HD 209458 b

Past Extrasolar Planet Discovery pulsar planet. Timeline • 1992 • 09/1995 • 11/1999 • 11/2001 • 1/2003 • 4/2004 Doppler extrasolar planet discoveries take off extrasolar planet transit extrasolar planet atmosphere planet discovered with transit method 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!