Investigating the structure of transiting planets, from hot Jupiters to Kepler super Earths

1. 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)

2. J E

3. 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

4. There is an incredibly diversity of worlds • We can also characterizethese 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

5. 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

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

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

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

9. 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

10. Explaining Large Radii An area of active research!

11. 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?

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

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

14. 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

15. 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

16. There is an incredibly diversity of worlds • We can also characterizethese planets, not just find them

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

18. 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?

19. Water World Model Mini Rocky Neptune Model Boundary in P(Mbar)/T(K)

20. Water World Model

21. The Atmosphere is the Key to understanding the Interior H2/He-dominated atmospheres Miller-Ricci & Fortney (2010) Bean et al. (2010)

22. 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

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

24. Borucki et al. (2011) Analysis: 2-3 RE Most Common Size

25. 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

26. Kepler-11: Picking out the Planets

27. Kepler-11: Lightcurves and Transit Times

28. 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

29. 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)

30. 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