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

Jonathan FortneyUniversity 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 RJ is the largest radius of a standard cooling model

Fortney et al. (2007)

Building a Model, II: Additional Interior Power

1 MJ planet with a 10 ME core, at 0.05 AU from the Sun

Miller, Fortney, & Jackson (2009)

Explaining Large RadiiAn 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 MJ

Solar=0.014

[Fe/H]<0.00.0≤[Fe/H]<0.20.2≤[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 Model Mini Rocky Neptune Model

Boundary in P(Mbar)/T(K)

Water World Model

H2/He-dominatedatmospheres

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• 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

•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 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