Earths and super-Earths Science Enabled by Direct Imaging Technology Renyu Hu, Ph.D. Jet Propulsion Laboratory California Institute of Technology Workshop on Technology for Direct Detec4on and Characterizaon of Exoplanets April 9, 2018 Pasadena CA Exoplanet Demography Commonality of Small Planets Jupiter Neptune Earth Transit Radial Velocity Imaging Microlensing 2 Detecting ExoPlanet Atmospheres In transit HAT-P-11b, a Neptune-sized planet 3 Fraine et al. 2014 H2 Atmospheres Detectable via transit HAT-P-11b, a Neptune-sized planet 14 TRA-1 h (2) 12 10 TRA-1 e (3) TRA-1 f (4) 8 TRA-1 g (6) 6 TRA-1 d (12) Obs Index of HST 4 HST Observable Obs Index of JWST / 2.7 K-16 b K2-18 b PH-2 b 2 LHS-1140 b K-167 e K2-3 d JWST Observable K2-9 b 0 100 120 140 160 180 200 220 240 260 280 300 320 Equ. Temp [K] 4 Non-H2 Atmospheres? Complicaon with stellar variability Transit Feature - Up to 10% for H2 atmospheres - <1% for non-H2 atmospheres Emission Feature - 1-2% 5 Rackham et al. 2018 Direct Detection of a Solar System Starshade Rendezvous Mission simulated image of a nearby star EXO-S Final 6 SeagerReport 2015 et al. 2015 Detecting Earths 7 8 How do we know whether an exoplanet has an atmosphere? whether an exoplanet’s atmosphere has evolved? whether an exoplanet has geological/biological acvies? 9 Detect Rocky Exoplanet Surfaces Spectral features of rocky planetary surfaces Reflec4vity Reflec4vity wavelength wavelength 10 Detect Rocky Exoplanet Surfaces Direct detec4on of rocky exoplanets Metal-rich Primary crust with mantle ripped off Ultramafic Primary crust with mantle overturn or secondary crust from hot lavas Feldspathic Primary crust without mantle overturn Basal4c Secondary crust Granitoid Ter4ary crust Clay Aqueously altered crust Ice-rich silicate Ice-rich surface Fe-oxidized Oxidave weathering 11 Hu et al. 2012 Delineate Land and Sea From phase curves of a rocky planet 12 Cowan et al. 2009 Rotation Period and Hydrological Cycle What we learned from DSCOVR observaons of Earth Minimum sampling rate is 10 hours 13 Jiang et al. 2018 How do we know whether an exoplanet has an atmosphere? whether an exoplanet’s atmosphere has evolved? whether an exoplanet has geological/biological acvies? 14 Detecting an Earth-like Atmosphere Water, Oxygen, and Carbon Dioxide O2 Turnbull et al. 2006 15 Detecting an Earth-like Atmosphere Importance of Clouds 0.35 0.3 0.25 H2O 0.2 Albedo 0.15 No Cloud Cumulus Cloud Cirrus Cloud 0.1 Mean 0.05 0 500 600 700 800 900 1000 Wavelength [nm] 16 Detecting Earths and Super-Earths Diverse atmospheric composi4on of rocky planets H2O Gaillard & Scaillet 2014 17 Continuum from Super-Earths to Sub-Neptunes Diversity of Atmospheres H2 – Rich 1 0.9 Chemically as Gas Giant Atmospheres 0.8 0.7 H , CO, Water-rich 2 Hydrocarbon 0.6 CH4, CO , Carbon H Atmosphere 2 -rich Carbon X H O 0.5 2 Atmosphere – Poor Depend on – Rich 0.4 Temperature 0.3 0.2 Oxygen-rich CO, CO 0.1 Atmosphere 2 0 0.1 0.2 0.5 1 2 5 10 XC/XO Hu & Seager 2014 H2 – Poor 18 A Special Case for Water Worlds Condensible-Rich Atmospheres Ding & Pierrehumbert 2016 19 Distinguish Water Worlds vs. Giant Planets In reflected light 0.7 H −Dominated Atmosphere, Cloud Deck at 0.4 Bars 2 H −Dominated Atmosphere, Cloud Deck at 2 Bars 2 −3 0.6 H O−Dominated Atmosphere, Cloud Deck < 10 Bars Interplay between clouds H O NH 2 2 3 and C, N, O abundances 0.5 H2O Haze Produc4on in Photochemical Processes 0.4 CH4 Neptunes and H2O-rich CH4 CH4 H2O 0.3 Super-Earths Geometric Albedo Geometric CH4 CH4 CH4 Spectral Degeneracies and 0.2 Informaon Content CH CH4 4 0.1 CH4 CH4 0 500 550 600 650 700 750 800 850 900 950 1000 Wavelength [nm] Hu 2014; 20 Filippatos & Hu in prep. How do we know whether an exoplanet has an atmosphere? whether an exoplanet’s atmosphere has evolved? whether an exoplanet has geological/biological acvies? 21 JWST/WFIRST/ Towards Characterizing Rocky Other space Exoplanets’ Atmospheres telescopes Atmosphere Radiative Chemistry Transfer Surface Atmospheric Planetary Source flux Composition Spectrum The image part with relationship 22 ID rId2 was not found in Characterize Rocky Exoplanets’ Atmospheres Volcanic emission controls O2 buildup in CO2 atmospheres 10−1 100 O O 3 101 2 O 10 2 3 Pressure [Pa] 10 104 5 10 −14 −12 −10 −8 −6 −4 −2 0 Escape of hydrogen is balanced 10 10 10 10 10 10 10 10 by a net oxidizing flux from the Mixing Ratio atmosphere to the ocean Solid: Earth-like vol. emission Dashed: Low vol. emission Doed: No vol. emission 23 Hu et al. 2012 Characterize Rocky Exoplanets’ Atmospheres O2 and CH4 together as a biosignature 24 Domagal-Goldman et al. 2014 Characterize Rocky Exoplanets’ Atmospheres Measuring volcanic outgassing 1 300 Transit H O CO H O H S 2 2 2 2 Earth X 1 SO 280 0.8 SO 2 - Ground-based transit surveys, TESS 2 H O H S SO Earth X 10 2 2 2 Earth X 100 H SO 2 4 260- James Webb Space Telescope Earth X 1000 Aerosols CO CO 2 0.6 2 SO Earth X 3000 2 S Aerosols (JWST, launch 2018) 8 240 0.4 CH 4 Transmission SO 220 2 0.2 Brightness Temperature [K] 200 N Atmosphere 2 N Atmosphere d = 0.1 µm 2 P d = 0.1 µm 0 180 P 0.1 0.2 0.5 1 2 5 10 20 50 100 5 8 10 20 30 50 80 100 Wavelength [microns] Wavelength [microns] 0.6 S Absorption S Aerosol Reflection N Atmosphere 8 8 2 d = 0.1 µm Direct imaging P 0.5 Earth X 3000 Earth X 1000 - Starshade Rendez-vous with WFIRST 0.4 Earth X 100 - Flagship concepts for 2020 Astrophysics Decadal Survey (HabEx + 0.3 Earth X 10 LUVOIR) Reflectivity 0.2 Earth X 1 0.1 0 0.1 0.2 0.3 0.5 1 2 3 Wavelength [microns] 25 Hu et al. 2013 Conclusion § Direct imaging will enable characterization of Earths and super-Earths § We may learn about: surface type, atmospheric H2O, O2, CO2, rotation period, variability of clouds § It may be hard to directly measure: size of planet, mass of atmosphere, liquid water ocean § Intrinsic widths of spectral features will determine the required resolution, and the need to measure variability will determine the required collection area We could not guess how different from us they (extraterrestrials) might be. Carl Sagan, Contact, 1985 27 Characterize Rocky Exoplanets’ Atmospheres Sensi4vity to atmospheric surface pressure 100 H O O CH 2 2 3 CO 4 How does O2 buildup depend on surface 10-2 pressure and irradiaon? 10-4 10-6 Column Mixing Ratio 10-8 Tre’Shunda James Intern at JPL 10-10 10-1 100 101 Surface Pressure [Bar] Oxygen buildup peaks at ~1 bar 28 James & Hu, in prep. Atmospheres of Wide-Separation Exoplanets Synergy between transit and direct imaging Transit spectrum of a 229-day-period exoplanet Kepler 16-b (HST GO 14927, PI Renyu Hu) 29 Copyright 2018 California Institute of Technology. U.S. Government sponsorship acknowledged. .