Trent Schindler

Trent Schindler

Sara Seager Massachusetts Institute of

Technology

Exoplanet Atmospheres: From Discovery to Characterization

and Beyond

Known Planets 1995

Based on data compiled by J. Schneider

Known Planets 1996

Based on data compiled by J. Schneider

Known Planets 2000

Based on data compiled by J. Schneider

Known Planets 2005

Based on data compiled by J. Schneider

Known Planets 2010

Based on data compiled by J. Schneider

Exoplanet Atmospheres Discovery Characterization

Beyond

Transiting Planet Science

Primary Eclipse Measure size of planet See star’s radiation transmitted through the planet atmosphere

Secondary Eclipse See planet thermal radiation disappear and reappear

Learn about atmospheric circulation from thermal phase curves

10-2

10-4

10-3

Courtesy Josh Winn

See Seager and Mallen-Ornelas 2003

Identification of Atoms and Molecules

H2O and CH4 in transmission from HST Swain et al. (2008) See also Grillmair et al. 2008.

HD 189733b Na, H2O, CH4 , CO2, CO, hazes

HD 209458b Na, H2O, CH4, CO, CO2, H Ly α

Day-Night Temperature Variation

NASA/ESA/G. Bacon Spitzer Space Telescope

Day-Night Temperature Variation

HD 189733

HD 189733b Knutson et al. 2007

HAT-P-7b Borucki et al. 2009

Thermal Phase Curves

HD 189733

HD 189733b Knutson et al. 2007

Hottest regions are shifted away from the substellar point are interpreted as advection by a prograde superrotating equatorial jet.

No model yet explains or predicts the westward-shifted cold spot

Variability

Madhusudhan and Seager, 2009

Data from: Swain et al. 2008, Charbonneau et al. 2008, Grillmair et al. 2008

Variability: CO2

From VPL website

10-18

10-18

10-21

10-21

10-21

A Comment on Data

Courtesy F. Pont

Data from Pont et al. 2008, Swain et al. 2008 Tinetti et al. 2007, Beaulieu et al. 2008, 2009, Desert et al. 2009. Figure courtesy Pont.

Disagreement in the literature in Spitzer data is gradually being resolved over time, due to understanding different approaches to systematics’ removal.

Tran

sit R

adiu

s (R

p/R*)

8 5 2 1 0.6 Wavelength (µm)

Identification of molecules Day-night temperature gradients Variability at 2-σ level Atmospheric escape Hot Jupiters are dark

Summary of Atmosphere Highlights

There is real data on exoplanet atmospheres. It may be limited, but many people are modeling the data

Exoplanet Atmospheres Discovery Characterization

Highlights Model Constraints

Beyond

Exoplanet Atmosphere Models

+

Get a recipe

Fit the data

Vary ingredients

=

Everything other than g and F*

Exoplanet atmosphere modeling is like cooking – S. Aigrain

Exoplanet Atmosphere Models

Previously unanswered questions •  What is the “best-fit” model? •  How is the best-fit quantified? •  Is the “best-fit” model unique? •  If the best-fit is not unique, what are the allowed ranges of

model parameters?

Charbonneau et al. 2008 Grillmair et al. 2008 Swain et al. 2008

Hot Jupiter Radiative Transfer

•  Stellar irradiation •  Intrinsic energy source

Boundary Conditions

Chemical Equilibrium

•  Day-night redistribution: •  Unknown opacity: •  Composition ( ) + clouds, etc.

Model Free Parameters •  No longer “self consistent” models •  Computation time and convergence •  Just a few models are run

Caveats

1D, plane parallel, LTE

€

dIλdτλ

= Iλ − Sλ

κλ Jλ − Sλ( )0

∞

∫ dλ = 0

dTdz

= −γ −1γ

µgkB

dPdz

= −ρg

P =ρkBT

µ

A Temperature and Abundance Retrieval Technique

Run millions of models to constrain T and abundances Madhusudhan and Seager, 2009 N. Madhusudhan PhD 2009

Atmosphere Temperature Profiles

HD 189733

Madhusudhan and Seager 2009

Grillmair et al. 2008 Charbonneau et al. 2008 Deming et al. 2006 Swain et al. 2008

Madhusudhan and Seager 2009

Result #1 Variability

Variability: True uncertainty in the data? Then no useful limits on molecular abundances Or the atmospheres are variable both in the energy redistribution state and in the concentrations of molecular abundances

Result #2 Quantitative Abundances

HD 189733 b Madhusudhuan and Seager 2009

Spitzer/IRAC

Result #2 Quantitative Abundances

HD 189733 b Madhusudhuan and Seager 2009

Spitzer/IRAC + HST/NICMOS

Result #3 Challenge to Thermal Inversion

Evidence for thermal inversion difficult to assess for most exoplanets, assuming 2 σ data uncertainties and/or a range of molecular abundances Madhusudhan and Seager, submitted to ApJ

Result #4 Lack of CH4 on the Hot Neptune GJ 436b

Stevenson et al. Nature 2010 Madhusudhan and Seager, submitted to ApJ

We have moved beyond discovery to characterization  several robust observational highlights  a quantitative tool for atmospheres

Atmosphere Summary

Exoplanet Atmospheres Discovery Characterization Beyond

de Mooij & Snellen 2009

Ground-Based Advances • Very Hot Jupiter secondary eclipses • Directly imaged Jupiters • Search for transiting super Earths

β Pictoris: New Planet

A composite image of the planet from 2003 and 2009 and the disk. Lagrange et al., Science 2010 (today)

The M Star Opportunity

Semi-Major Axis

Sun

K2

M6

Probability = 1/200 P = 365 days Transit depth = 10-4

Probability = 1/140 P = 177 days Transit depth = 1.25 x10-4

Probability = 1/50 P = 13 days Transit depth = 0.001 Tidally-locked

John E. Kauffman used with permission

Radiative transfer

Atmospheric Composition

Chemical equilibrium/disequilibrium

Photochemistry

Atmospheric escape

Atmospheric circulation

Connection with observations

Clouds

JWST = TPF?

Lecture #3 Wed. June 23

Earth’s Spectrum

Turnbull et al. 2007

Pearl and Christensen 1997

Lecture #3 Wed. June 23

•  Discovery –  Hundreds of exoplanets are known –  Atmosphere measurements for over dozens

•  Characterization –  A few robust observational highlights show that exoplanet

atmospheres are being studied in detail –  Models are required to solidify interpretation

•  Beyond –  Direct imaging of hot young planets –  The M star opportunity: searching for super Earths orbiting close to low-mass stars and planned characteriztiaon with JWST

Summary

Trent Schindler

Trent Schindler

Seager & Deming, Annual Reviews of Astronomy and Astrophysics, 09/2010

Madhusudhan and Seager ApJ, 2009

Seager, “Exoplanet Atmospheres: Physical Processes” 2010, Princeton University Press

References