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Glimpsing the Compositions of Sub-Neptune-Size Exoplanets

Glimpsing the Compositions of Sub-Neptune-Size Exoplanets. Leslie Rogers Hubble Fellow California Institute of Technology larogers@caltech.edu. Kepler Science Conference II – November 4, 2013. Kepler- 22b: R p = 2.4 R . Rocky. OR. M p <124 M  P orb = 290 days

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Glimpsing the Compositions of Sub-Neptune-Size Exoplanets

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  1. Glimpsing the Compositions of Sub-Neptune-Size Exoplanets Leslie Rogers Hubble Fellow California Institute of Technology larogers@caltech.edu Kepler Science Conference II – November 4, 2013

  2. Kepler-22b: Rp= 2.4 R Rocky OR • Mp<124 M • Porb = 290 days • Borucki et al. (2012) Volatile Rich? Figure Credit: NASA/Ames/JPL-Caltech

  3. Six Years Ago 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations

  4. Non-KeplerPlanets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations

  5. Kepler Planets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations

  6. Masses & Radii of 49 Planets from KeplerMarcy et al. (2013) submitted • Radial velocity follow-up observations of 22 sub-Neptune-size KOIs with Keck-HIRES • Selection Criteria: • Planet candidates smaller than 4 REarth • Predicted RV amplitude detectable (K > 1m s-1) • Stellar Properties: Kp < 13.5, Teff<6100K, vsini< 5 km s-1 • Results: • 42 Transiting Planets, 7 Non-Transiting planets in 22 planetary systems • 16 transiting planets have strong mass measurements, rest have marginal RV detections or mass upper limits

  7. Kepler Planets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations

  8. New KeplerPlanet Masses from Keck RVs 100% H2O 100% Silicate 100% Iron Marcy et al. (in prep) Seager et al. (2007) M-R Relations

  9. New Kepler Planet Masses from Keck RVs

  10. Which Planets Are Rocky?

  11. Which Planets Are Rocky?

  12. Which Planets Are Rocky? Non-Rocky

  13. Which Planets Are Rocky? Non-Rocky Potentially Rocky

  14. Smaller Planets are Denser Potentially Rocky How does the Fraction of Planets Dense Enough to be Rocky vary with Rp? Non-Rocky

  15. Model:

  16. Radius Mass

  17. Radius Mass

  18. Simplest Model for frocky(Rp): Step Function frocky(Rp) (Fraction of planets that are rocky) 1 model parameter: Rocky/Non-Rocky Radius Threshold

  19. Step-Function Model:Radius Upper Limit for Rocky Planets Rogers 2014 (submitted)

  20. Step-Function Model:Radius Upper Limit for Rocky Planets Median 1.48 +0.04 -0.05 R Rogers 2014 (submitted)

  21. Step-Function Model:Radius Upper Limit for Rocky Planets 95% Confidence Upper Bound 1.59 +0.18 -0.05 R Median 1.48 +0.04 -0.05 R Rogers 2014 (submitted)

  22. Model #2 for frocky(Rp): Linear Transition frocky(Rp) (Fraction of planets that are rocky) 2 model parameters: Rmid transition midpoint DR transition width

  23. Linear Transition Model:Radius Limits for Rocky / Non-Rocky Planets R50% rocky = 1.48 +0.16 -0.50R < 1.61 R (95% conf.) Rogers 2014 (submitted)

  24. Linear Transition Model:Posterior Distribution for frocky(Rp) p(frocky|Rp, data) Rogers 2014 (submitted)

  25. Bayesian Evidence Prefers Simpler 1-parameter Step Function Model Preferred E1 ~ 5 E2 Model 1: Step Function 1 parameter Model 2: Linear Transition 2parameters

  26. Main Take Away: Most planets larger than 1.6 R are not Rocky. • Kepler-22b • (Rp= 2.4 R): Rocky OR Volatile Rich? Figure Credit: NASA/Ames/JPL-Caltech

  27. Extra Slides Leslie Rogers Hubble Fellow California Institute of Technology larogers@caltech.edu Kepler Science Conference II – November 4, 2013

  28. Incident Flux Dependent frocky? Non-Rocky Potentially Rocky 102 100 101 104 103

  29. Smaller Planets are Denser Potentially Rocky Non-Rocky

  30. Linear Transition Model:Predictive Distribution of frocky(Rp)

  31. Probability a Planet is Sufficiently Dense to be Rocky, procky Non-Rocky 100% Silicate Potentially Rocky Seager et al. (2007) M-R Relations

  32. Planets Detected both Dynamically and in Transit are Valuable! Stellar Wobble Transits Planet Mass Planet Radius Planet Density

  33. Super-Earth and Sub-Neptune Planets • Uranus & Neptune • 15 M • 4 R • Earth1 M • 1 R

  34. Super-Earth and Sub-Neptune Planets • Uranus & Neptune • 15 M • 4 R • 1.6 R • Earth1 M • 1 R

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