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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) J E 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 shortperiod orbits July 2007 There is an incredibly diversity of worlds We can also characterize these planets, not just find them Late 2006 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 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 Fortney, Baraffe, & Militzer (2010) At Gyr ages, ~1.3 RJ is the largest radius of a standard cooling model Fortney et al. (2007) Building a Model, II: Additional Interior Power Miller, Fortney, & Jackson (2009) 1 MJ planet with a 10 ME core, at 0.05 AU from the Sun 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? There is an emerging population of planets with no radius anomaly Miller & Fortney (2011), submitted A strong correlation between star and planet abundances Miller & Fortney (2011), submitted See also, Guillot et al. (2006) A quasi-uniform super-solar enrichment above 0.5 MJ [Fe/H]<0.0 0.0≤[Fe/H]<0.2 0.2≤[Fe/H]<0.4 Solar=0.014 Miller & Fortney (2011), submitted 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 •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 •Massive planets and low-mass brown dwarfs should have structural and atmospheric abundance differences There is an incredibly diversity of worlds We can also characterize these planets, not just find them Charbonneau et al. (2009) GJ1214b: A “Super Earth” orbiting a nearby bright M star What is the Nature of the Planet’s Atmosphere and Interior? •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? Water World Model Mini Rocky Neptune Model Boundary in P(Mbar)/T(K) Water World Model The Atmosphere is the Key to understanding the Interior H2/He-dominated atmospheres 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 • 1200+ transiting planet candidates • d < 0.25 AU Borucki et al. (2011) Analysis: 2-3 RE Most Common Size Analysis of first 4 months of data---much more still to come Borucki et al. (2011) Analysis: 2-3 RE Most Common Size Kepler-11 •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: Picking out the Planets Kepler-11: Lightcurves and Transit Times Kepler-11: The Mass-Radius View GJ 1214b • Modeled as rock-iron cores with water or H/He envelopes • Atmospheric escape with time is ignored Atmospheric Gain and Loss CoRoT-7b Jackson et al. (2010) • In the Kepler-11 system, significantly more massive planets can be ruled out from stability considerations, particularly for the inner 2 planets Alibert et al. (2005) Conclusions • A batch of new discoveries show that “mini-Neptunes” may be a common (the most common?) type of planet • The processes that affect H2-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