Sara Seager - Lecture1 - MIT
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The document summarizes the discovery and characterization of exoplanet atmospheres over time. It discusses key observational highlights including the identification of molecules, day-night temperature variations, and variability in some atmospheres. Modeling techniques are also described that aim to constrain atmospheric properties by fitting millions of models to data. The summary outlines progress made but also future directions, such as direct imaging of young planets and the potential for characterizing small planets around M stars.
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Sara Seager - Lecture1 - MIT
- 1. Exoplanet Atmospheres: From Discovery to Characterization and Beyond Trent Schindler Trent Schindler Sara Seager Massachusetts Institute of Technology
- 2. Known Planets 1995 Based on data compiled by J. Schneider
- 3. Known Planets 1996 Based on data compiled by J. Schneider
- 4. Known Planets 2000 Based on data compiled by J. Schneider
- 5. Known Planets 2005 Based on data compiled by J. Schneider
- 6. Known Planets 2010 Based on data compiled by J. Schneider
- 7. Exoplanet Atmospheres Discovery Characterization Beyond
- 8. 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
- 9. Courtesy Josh Winn See Seager and Mallen-Ornelas 2003
- 10. 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
- 11. Day-Night Temperature Variation NASA/ESA/G. Bacon Spitzer Space Telescope
- 12. Day-Night Temperature Variation HD 189733 HD 189733b Knutson et al. 2007 HAT-P-7b Borucki et al. 2009
- 13. 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
- 14. Variability Madhusudhan and Seager, 2009 Data from: Swain et al. 2008, Charbonneau et al. 2008, Grillmair et al. 2008
- 15. Variability: CO2 10-18 10-21 10-21 10-21 10-18 From VPL website
- 16. A Comment on Data Courtesy F. Pont Transit Radius (Rp/R*) 8 0.6 1 2 5 Wavelength (μm) 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.
- 17. Summary of Atmosphere Highlights Identification of molecules Day-night temperature gradients Variability at 2-σ level Atmospheric escape Hot Jupiters are dark There is real data on exoplanet atmospheres. It may be limited, but many people are modeling the data
- 18. Exoplanet Atmospheres Discovery Characterization Highlights Model Constraints Beyond
- 19. 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
- 20. Exoplanet Atmosphere Models Charbonneau et al. 2008 Swain et al. 2008 Grillmair et al. 2008 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?
- 21. Hot Jupiter Radiative Transfer 1D, plane parallel, LTE Boundary Conditions • Stellar irradiation • Intrinsic energy source Chemical Equilibrium ∞ ∫ dλ = 0 dT dz Model Free Parameters • Day-night redistribution: • Unknown opacity: • Composition ( ) + clouds, etc. Caveats • No longer “self consistent” models • Computation time and convergence • Just a few models are run € dIλ dτ λ = Iλ − Sλ κλ Jλ − Sλ ( ) 0 = − γ −1 γ μg kB dP dz = −ρg P = ρkBT μ
- 22. A Temperature and Abundance Retrieval Technique Run millions of models to constrain T and abundances Madhusudhan and Seager, 2009 N. Madhusudhan PhD 2009
- 24. HD 189733 Madhusudhan and Seager 2009 Grillmair et al. 2008 Charbonneau et al. 2008 Deming et al. 2006 Swain et al. 2008
- 25. 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 Madhusudhan and Seager 2009
- 26. Result #2 Quantitative Abundances Spitzer/IRAC HD 189733 b Madhusudhuan and Seager 2009
- 27. Result #2 Quantitative Abundances Spitzer/IRAC + HST/NICMOS HD 189733 b Madhusudhuan and Seager 2009
- 28. 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
- 29. Result #4 Lack of CH4 on the Hot Neptune GJ 436b Stevenson et al. Nature 2010 Madhusudhan and Seager, submitted to ApJ
- 30. Atmosphere Summary We have moved beyond discovery to characterization several robust observational highlights a quantitative tool for atmospheres
- 31. Exoplanet Atmospheres Discovery Characterization Beyond
- 32. Ground-Based Advances de Mooij & Snellen 2009 • Very Hot Jupiter secondary eclipses • Directly imaged Jupiters • Search for transiting super Earths
- 33. β Pictoris: New Planet A composite image of the planet from 2003 and 2009 and the disk. Lagrange et al., Science 2010 (today)
- 34. 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
- 35. John E. Kauffman used with permission
- 36. Atmospheric escape Photochemistry Radiative transfer Atmospheric Composition Chemical equilibrium/disequilibrium Atmospheric circulation Clouds Connection with observations
- 37. JWST = TPF? Lecture #3 Wed. June 23
- 38. Earth’s Spectrum Turnbull et al. 2007 Pearl and Christensen 1997 Lecture #3 Wed. June 23
- 39. Summary • 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
- 40. Seager & Deming, Annual Reviews of Astronomy and Astrophysics, 09/2010 Madhusudhan and Seager ApJ, 2009 Seager, “Exoplanet Atmospheres: Physical Processes” 2010, Princeton University Press Trent Schindler Trent Schindler References