Investigating the structure of transiting planets, from hot Jupiters to Kepler super Earths Jonathan Fortney University of California, Santa Cruz Thanks to: Neil Miller (UCSC), Eric Lopez (UCSC) Eliza Miller-Ricci Kempton (UCSC), Nadine Nettelmann (U. of Rostock)

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Transiting Planets, Large and Small  110 planets have now been seen to transit their parent stars  99 “hot Jupiters”  5 “hot Neptunes”  6 “super Earths”  Combination of planet radius and mass yield density - -> composition  Strong bias towards finding mass/large planets on short- period orbits July 2007

Late 2006  We can also characterize these planets, not just find them There is an incredibly diversity of worlds The shear number of discoveries opens up the prospect of understanding gas giants (Jupiter-like), ice giants (Neptune-like) and lower mass planets as classes of astrophysical objects

Charbonneau, et al., 2007  There is considerable diversity amongst the known transiting planets  Radii for planets of similar masses differ by a factor of two, which cannot happen for pure H/He objects

Fortney, Baraffe, & Militzer (2010) Our Gas Giant Prototypes: Jupiter and Saturn 5-25% Heavy Elements by Mass

Fortney, Baraffe, & Militzer (2010) Our Ice Giant Prototypes: Uranus and Neptune 80-90% Heavy Elements by Mass

At Gyr ages, ~1.3 R J is the largest radius of a standard cooling model Fortney et al. (2007)

Building a Model, II: Additional Interior Power 1 M J planet with a 10 M E core, at 0.05 AU from the Sun Miller, Fortney, & Jackson (2009)

Explaining Large Radii An area of active research!

Beyond Radius Inflation: What are We Trying to Learn? We’d like to understand giant planets as a class of astrophysical objects What are their unifying properties?

Miller & Fortney (2011), submitted There is an emerging population of planets with no radius anomaly

Miller & Fortney (2011), submitted A strong correlation between star and planet abundances See also, Guillot et al. (2006)

Miller & Fortney (2011), submitted A quasi-uniform super-solar enrichment above 0.5 M J Solar=0.014 [Fe/H]< ≤[Fe/H]< ≤[Fe/H]<0.4

Implications for Giant Planets Giant planets, as a class, are enriched in heavy elements Enriched compared to the Sun Enriched compared to their parent stars Enrichment is a strong inverse function of mass, but with an apparent “floor” at high mass Massive planets and low-mass brown dwarfs should have structural and atmospheric abundance differences The heavy element mass of an inflated planet could be estimated only from its stellar metallicity With that in hand, its additional interior power could be constrained Radius inflation mechanism can be studied vs. orbital separation and planet mass

 We can also characterize these planets, not just find them There is an incredibly diversity of worlds

GJ1214b: A “Super Earth” orbiting a nearby bright M star Charbonneau et al. (2009)

Mass-Radius leads to degenerate solutions: Mostly water with a small rocky core A “failed” giant planet core? Lower ice/rock ratio, with a H/He envelope A mini Neptune? What is the cooling history and interior state of these two kinds of models? What is the Nature of the Planet’s Atmosphere and Interior?

Water World ModelMini Rocky Neptune Model Boundary in P(Mbar)/T(K)

Water World Model

H 2 /He-dominated atmospheres The Atmosphere is the Key to understanding the Interior Miller-Ricci & Fortney (2010) Bean et al. (2010)

The Kepler Mission Monitoring 150,000 stars for 3.5+ years 20 months into the mission First 4 months is now public transiting planet candidates d < 0.25 AU

Borucki et al. (2011) Analysis: 2-3 R E Most Common Size Analysis of first 4 months of data---much more still to come

Borucki et al. (2011) Analysis: 2-3 R E Most Common Size

The most densely-packed planetary system yet found 5 planets within the orbit of Mercury Masses obtained only from Transit Timing Variations, with no Stellar RV Relatively low density for all planets implies thick H/He atmospheres Kepler-11

Kepler-11: Picking out the Planets

Kepler-11: Lightcurves and Transit Times

Kepler-11: The Mass-Radius View Modeled as rock-iron cores with water or H/He envelopes Atmospheric escape with time is ignored GJ 1214b

Atmospheric Gain and Loss Jackson et al. (2010) Alibert et al. (2005) CoRoT-7b In the Kepler-11 system, significantly more massive planets can be ruled out from stability considerations, particularly for the inner 2 planets

Conclusions A batch of new discoveries show that “mini-Neptunes” may be a common (the most common?) type of planet The processes that affect H 2 -dominated atmosphere gain/escape should be investigated in much more detail The Kepler-11 system is a natural laboratory to study atmospheric mass loss Planet types keep emerging that we have no analog for in the solar system We can now begin to understand the structure of giant planets with lower-irradiation transiting planets Kepler has already found a larger sample of these types of planets, but follow-up observations for masses must be done