leslie rogers hubble fellow california institute of technology larogers@caltech.edu kepler science...

Leslie RogersHubble Fellow

California Institute of Technologylarogers@caltech.edu

Kepler Science Conference II – November 4, 2013

Glimpsing the Compositions of Sub-Neptune-Size Exoplanets

Mp <124 M

Porb = 290 days

Borucki et al. (2012)Figure Credit: NASA/Ames/JPL-Caltech

Rocky

Volatile Rich?OR

Kepler-22b: Rp = 2.4 R

Six Years Ago

100% Silicate100% H2O

100% Iron

Seager et al. (2007) M-R Relations

Non-Kepler Planets

100% Silicate100% H2O

100% Iron

Seager et al. (2007) M-R Relations

Kepler Planets

100% Silicate100% H2O

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% Silicate100% H2O

100% Iron

Seager et al. (2007) M-R Relations

New Kepler Planet Masses from Keck RVs

100% Silicate100% H2O

100% Iron

Seager et al. (2007) M-R Relations Marcy et al. (in prep)

New Kepler Planet Masses from Keck RVs

Which Planets Are Rocky?

Which Planets Are Rocky?

Which Planets Are Rocky?

Non-Rocky

Which Planets Are Rocky?

Potentially Rocky

Non-Rocky

Smaller Planets are DenserPotentially Rocky

Non-Rocky

How does the Fraction of Planets Dense Enough to be Rocky vary with Rp?

Model:

Mass

Radius

Mass

Radius

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

Median 1.48 +0.04

-0.05 R

95% Confidence Upper Bound 1.59 +0.18

-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 midpointDR transition width

Linear Transition Model:Radius Limits for Rocky / Non-Rocky Planets

R50% rocky = 1.48 +0.16

-0.50 R

< 1.61 R (95% conf.)

Rogers 2014 (submitted)

Linear Transition Model:Posterior Distribution for frocky(Rp)

p(frocky |R

p , da

ta)

Rogers 2014 (submitted)

Bayesian Evidence Prefers Simpler 1-parameter Step Function Model

Model 1: Step Function1 parameter

Model 2: Linear Transition2 parameters

Preferred E 1 ~ 5 E 2

Figure Credit: NASA/Ames/JPL-Caltech

Main Take Away: Most planets larger than 1.6 R are not Rocky.

Rocky

Volatile Rich?OR

Kepler-22b(Rp = 2.4 R):

Leslie RogersHubble Fellow

California Institute of Technologylarogers@caltech.edu

Extra Slides

Kepler Science Conference II – November 4, 2013

Incident Flux Dependent frocky?Non-Rocky

Potentially Rocky

100 101 104102 103

Smaller Planets are DenserPotentially Rocky

Non-Rocky

Linear Transition Model:Predictive Distribution of frocky(Rp)

Non-Rocky

Potentially Rocky

100% Silicate

Probability a Planet is Sufficiently Dense to be Rocky, procky

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

Earth1 M

1 R

Uranus & Neptune15 M

4 R

Super-Earth and Sub-Neptune Planets

Earth1 M

1 R

Uranus & Neptune15 M

4 R

1.6 R