Colors of Alien Worlds from Direct-Imaging Exoplanet Missions Renyu Hu Hubble Fellow Jet Propulsion Laboratory California Institute of Technology With thanks to Wesley Traub (JPL)

HD b Evans et al. 2013; Image Credit: NASA, ESA, and G. Bacon (STScI)

Why reflection is hard? Seager & Deming 2010 Contrast of typical hot Jupiters Infrared ~ Optical ~ Contrast of Jupiters Optical ~ 10 -8

WFIRST-AFTA Courtesy of Wesley Traub (JPL) Giant exoplanets at 2 – 4 AU

What can we learn about giant exoplanets from their reflection spectra?

Fundamental Quantities Atmospheric Elemental Abundance Internal Heat Flux Irradiation Environment Observable Quantities Atmospheric Molecular Composition Cloud Properties Observation Signatures Reflection Spectrum Controlling Factors Atmosphere Chemistry & Dynamics Radiation Transfer

Jupiter as a Test Case Hu 2014

Cool Giant Exoplanets Hu 2014 Type and location of clouds depend on Atmospheric composition Thermal evolution history and beyond 1-D models Updraft and downdraft Deep liquid water clouds dissolving ammonia

Sample Spectra Hu 2014

Degeneracy! Hu 2014

Detectability of Cloud and Gas Hu 2014 Cloud top pressure

Detectability of Cloud and Gas Hu 2014 Cloud top pressure

Detectability of Cloud and Gas Hu 2014 Cloud top pressure χ 2 can be defined as the difference between a model and all adjacent models, for specified spectral resolution and SNR

Detectability of Cloud and Gas Hu 2014 Jupiter HD e Ups And e

Hu 2014 Strong Band trace the methane column above cloud Weak Band probe the cloud top pressure between 0.4 and 1.2 bars

Towards Imaging (Super-)Earths

Cool H 2 O-rich Super Earths Hu 2014

Direct-imaging exoplanet missions may offer the capability to broadly distinguish H 2 -rich giant exoplanets versus H 2 O-rich super-Earth exoplanets, and to detect ammonia and/or water clouds and methane gas in their atmospheres Renyu Hu, 2014, Ammonia, Water Clouds and Methane Abundances of Giant Exoplanets and Opportunities for Super-Earth Exoplanets, Report delivered to the EXEP (arXiv: ) Pressure of Ammonia or Water Clouds Relative strength between the strong and weak bands of methane Abundance of Methane Strength of the methane bands H2O-rich Super Earths High clouds and low methane abundances Conclusion

Hu 2014 Color-Color Diagram

Learning from Jupiter Observations Hu 2014

Learning from Jupiter Observations Sato & Hansen 1979

Detectability of Cloud and Gas Hu 2014

What do optical phase curves tell us about exoplanets?

Phase Curve of Kepler-7 b Demory et al A g =0.35±0.02 Phase offset

Two Scenarios Hu et al Planetary Flux = Thermal Emission + Symmetric Reflection + Asymmetric Reflection

Hu et al Homogeneous Atmosphere Phase offset attributed to thermal emission A B =0.18±0.03 T photo /T eq =1.23±0.02 t rad /t adv =-0.32±0.05 Patchy Cloud Phase offset attributed to reflection A B =0.42±0.01 r clear <7% r cloudy >80% Cloud boundary 11±3° to the west (cloud condenses at 1500 – 1700 K)

Two Solutions for a Phase Offset Hu et al How to break the degeneracy? Measure the planet’s flux at a longer wavelength Modeling atmospheric circulation

Phase offsets are common! Shporer & Hu 2015, submitted