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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 Leslie Rogers Hubble Fellow California Institute of Technology larogers@caltech.edu Kepler Science Conference II – November 4, 2013
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
Six Years Ago 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations
Non-KeplerPlanets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations
Kepler Planets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations
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
Kepler Planets 100% H2O 100% Silicate 100% Iron Seager et al. (2007) M-R Relations
New KeplerPlanet Masses from Keck RVs 100% H2O 100% Silicate 100% Iron Marcy et al. (in prep) Seager et al. (2007) M-R Relations
Which Planets Are Rocky? Non-Rocky
Which Planets Are Rocky? Non-Rocky Potentially Rocky
Smaller Planets are Denser Potentially Rocky How does the Fraction of Planets Dense Enough to be Rocky vary with Rp? Non-Rocky
Radius Mass
Radius Mass
Simplest Model for frocky(Rp): Step Function frocky(Rp) (Fraction of planets that are rocky) 1 model parameter: Rocky/Non-Rocky Radius Threshold
Step-Function Model:Radius Upper Limit for Rocky Planets Rogers 2014 (submitted)
Step-Function Model:Radius Upper Limit for Rocky Planets Median 1.48 +0.04 -0.05 R Rogers 2014 (submitted)
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)
Model #2 for frocky(Rp): Linear Transition frocky(Rp) (Fraction of planets that are rocky) 2 model parameters: Rmid transition midpoint DR transition width
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)
Linear Transition Model:Posterior Distribution for frocky(Rp) p(frocky|Rp, data) Rogers 2014 (submitted)
Bayesian Evidence Prefers Simpler 1-parameter Step Function Model Preferred E1 ~ 5 E2 Model 1: Step Function 1 parameter Model 2: Linear Transition 2parameters
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
Extra Slides Leslie Rogers Hubble Fellow California Institute of Technology larogers@caltech.edu Kepler Science Conference II – November 4, 2013
Incident Flux Dependent frocky? Non-Rocky Potentially Rocky 102 100 101 104 103
Smaller Planets are Denser Potentially Rocky Non-Rocky
Linear Transition Model:Predictive Distribution of frocky(Rp)
Probability a Planet is Sufficiently Dense to be Rocky, procky Non-Rocky 100% Silicate Potentially Rocky Seager et al. (2007) M-R Relations
Planets Detected both Dynamically and in Transit are Valuable! Stellar Wobble Transits Planet Mass Planet Radius Planet Density
Super-Earth and Sub-Neptune Planets • Uranus & Neptune • 15 M • 4 R • Earth1 M • 1 R
Super-Earth and Sub-Neptune Planets • Uranus & Neptune • 15 M • 4 R • 1.6 R • Earth1 M • 1 R