Characterizing Gas and Ice Giant Planets with LUVOIR

Mark Marley NASA Ames Research Center Why Giants?

• First directly imaged planets to be characterized in reflected light

• Proving ground for many reflected light challenges (clouds, hazes, abundances, radii, gravity, T, ….)

• Context for directly imaged terrestrial worlds

• WFIRST will not do all that needs to be done HST (mag) magnitude delta GPI JWST

WFIRST Planet/StarContrast

Angular Separation (arcsec) HST (mag) magnitude delta GPI JWST

WFIRST Planet/StarContrast

Angular Separation (arcsec) HST (mag) magnitude delta GPI JWST

WFIRST Planet/StarContrast

Angular Separation (arcsec) Today • Giant planet visible spectra 101

• What do we want to know?

• How do we find out?

• Cloud heights from narrow band images

• Methane abundance from spectra

• What will and won’t WFIRST do?

• Lessons for space based coronagraphs Giant Planet Spectra 101

CH4 H O 2 Na, K Clouds are the controlling influence on Bond Albedo CH4 and Teq H O 2 Na, K Clouds are the controlling influence on Bond Albedo CH4 and Teq H O 2 Na, K Temperature structure (set by stellar flux) controls chemistry & clouds. Temperature structure (set by stellar flux) controls chemistry & clouds.

all solar system planets P ERSPECTIVES outflow from it: It contains many forbidden Space Telescope (launched in August 2003) 4. A. Boss, Astrophys. J. 551, L167 (2001). emission lines (15, 16), which are usually as- and millimeter observations with ground- 5. B. Reipurth, C. Clarke, Astron. J. 122, 432 (2001). sociated with young stars in which a fraction based radio telescopes may reveal the sizes 6. M. R. Bate, I. A. Bonnell, V. Bromm, Mon. Not. R. Astron. Soc. 332, L65 (2002). of the inflowing material is ejected perpen- and masses of brown dwarf disks, allowing 7. A. A. Muench et al., Astrophys. J. 558,L51 (2001). dicular to the disk. If confirmed through fu- us to determine whether most disks are 8. A. Natta et al., Astron. Astrophys. 393, 597 ture observations, this finding would further truncated. Better statistics of the frequency (2002). 9. R. Jayawardhana et al., Astron. J. 126, 1515 (2003). strengthen the analogy between nascent of binary brown dwarfs could provide an- 10. M. Liu et al., Astrophys. J. 585, 372 (2003). brown dwarfs and their stellar counterparts. other observational test. Infrared studies of 11. R. Jayawardhana, S. Mohanty, G. Basri, Astrophys. J. The mounting evidence thus points to a even younger “proto-brown dwarfs,” which 578,L141 (2002). similar infancy for Sun-like stars and brown are still embedded in a dusty womb, may 12. R. Jayawardhana, S. Mohanty, G. Basri, Astrophys. J. 592, 282 (2003). dwarfs. Does this mean that the two kinds also provide clues to their origin. 13. J. Muzerolle et al., Astrophys. J. 592, 266 (2003). of objects are born in the same way? Many 14. S. Mohanty, R. Jayawardhana, D. Barrado y Navascués, observers tend to think so (7–12), but it References Astrophys. J. 593, L109 (2003). may be too early to rule out the ejection 1. G. Basri, Mercury 32, 27 (2003). 15. M. Fernández, F. Comerón, Astron. Astrophys. 380, 2. K. Lodders, Science 303, 323 (2004). 264 (2001). scenario for at least some brown dwarfs. 3. C. Low, D. Lynden-Bell, Mon. Not. R. Astron. Soc. 176, 16. D. Barrado y Navascués, S. Mohanty, R. Jayawardhana, Far-infrared observations with the Spitzer 367 (1976). Astrophys. J., in press.

ASTRONOMY lish a firm reference frame for the spectral classification of L and T dwarfs. Brown Dwarfs—Faint at Heart, Such observations represent major progress, because small sizes (roughly the radius of Jupiter) and low masses hamper Rich in Chemistry the detection of brown dwarfs. Their mass- es only reach up to ~7% that of the Sun (for Katharina Lodders comparison, Jupiter’s mass is ~0.1%), not enough to initiate and sustain the hydrogen

decade ago, brown dwarfs were not to those of giant planets, but are much burning that powers real stars. Brown on June 8, 2009 much more than a theoretical curios- more massive. Brown dwarfs are further dwarfs may burn deuterium if they exceed Aity in astronomy textbooks. It was divided into subtypes from zero for the 13 Jupiter masses. However, the energy re- unclear whether such objects, with masses hottest (L0, T0) to eight for the coolest (L8, leased by this deuterium burning is a small and temperatures between the giant planets T8), depending on whether certain spectral fire compared to the inferno of hydrogen and the coolest known dwarf stars, even features assumed to be a proxy of temper- burning in stars and lasts less than 100 mil- existed. Today, the problem is how to tell ature are present. Today, ~250 L dwarfs lion years for the most massive brown all the different low-mass objects apart. In and ~50 T dwarfs are known (9). dwarfs. In contrast, hydrogen can burn for a recent paper in Astrophysical Journal, Initially, subtyping of L dwarfs was several billion years in dwarf stars (10).

McLean et al. (1) propose a unified classi- based on red optical spectra, whereas T Much of the energy released by a brown www.sciencemag.org fication scheme for brown dwarfs on the dwarfs were sorted by near-infrared spectral dwarf over its lifetime is from gravitation- basis of near-infrared spectra. The scheme features (5–8). McLean et al. (1) have now al energy gained during its formation and also provides insights into the chemistry of advanced a unified classification scheme contraction. A brown dwarf’s main fate is these cool, dense objects. [For a discussion for L and T dwarfs based on ~50 objects an- to sit and cool in space. of brown dwarf origins, see (2).] alyzed with the Keck II Near-Infrared Deprived of a nuclear engine, brown The first brown dwarf, prosaically Spectrometer. They have used the high- dwarfs never exceed ~3000 K near their sur- called Gl229 B, was discovered in 1995 (3, quality near-infrared spectra to categorize faces. The more a brown dwarf cools, the

4). It was clearly substellar, sharing more brown dwarfs by the relative strengths of the less it is visible at optical wavelengths. M Downloaded from characteristics with giant planets like atomic lines of Na, K, Fe, Ca, Al, and Mg dwarf stars emit most strongly at red wave- Jupiter than with red M dwarfs, the coolest andCondensate bands of water, carbon monoxide, Cloudlengths (~0.75 µ m),Layers but maximum emis- and lowest mass stars known at the time. methane, and FeH. The observations estab- sions of the cooler L dwarfs (1200 to 2000 Many more brown dwarfs were discovered in the late 1990s thanks to large-scale in- frared sky searches [Two Micron All Sky NH3 CH4 gas CO gas CO gas NH4HS Survey (2MASS), Deep Survey of the Perovskite Corundum H2O KCl Southern Sky (DENIS), and Sloan Digital Mg-silicates CH4 gas CH gas 4 Iron metal liquid CO gas Sky Survey (SDSS)]. CsCl LiF RbCl Li2S Brown dwarfs fall in two spectral class- Na2S KCl CO gas es, L and T (5–8). L dwarfs, which are closer to M dwarfs than to giant planets in LiF CO gas Li2S Perovskite Corundum spectral appearance, include the lightest re- Na2S Mg-silicates al stars and the heaviest substellar objects. CO gas Iron metal liquid T dwarfs have spectra that are more similar Mg-silicates Deeper Iron metal liquid Perovskite Corundum Hotter CO gas CO gas Denser Perovskite Corundum The author is at the Planetary Chemistry Laboratory, Jupiter T dwarfs L dwarfs L to M dwarf transition Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA. A cloudy picture. Cloud layers for Jupiter, T dwarfs, L dwarfs, and objects near theLodders transition (2004) from E-mail: [email protected] L to M dwarfs. The layers are progressively stripped off as the temperature of the object increases. www.sciencemag.org SCIENCE VOL 303 16 JANUARY 2004 323 P ERSPECTIVES outflow from it: It contains many forbidden Space Telescope (launched in August 2003) 4. A. Boss, Astrophys. J. 551, L167 (2001). emission lines (15, 16), which are usually as- and millimeter observations with ground- 5. B. Reipurth, C. Clarke, Astron. J. 122, 432 (2001). sociated with young stars in which a fraction based radio telescopes may reveal the sizes 6. M. R. Bate, I. A. Bonnell, V. Bromm, Mon. Not. R. Astron. Soc. 332, L65 (2002). of the inflowing material is ejected perpen- and masses of brown dwarf disks, allowing 7. A. A. Muench et al., Astrophys. J. 558,L51 (2001). dicular to the disk. If confirmed through fu- us to determine whether most disks are 8. A. Natta et al., Astron. Astrophys. 393, 597 ture observations, this finding would further truncated. Better statistics of the frequency (2002). 9. R. Jayawardhana et al., Astron. J. 126, 1515 (2003). strengthen the analogy between nascent of binary brown dwarfs could provide an- 10. M. Liu et al., Astrophys. J. 585, 372 (2003). brown dwarfs and their stellar counterparts. other observational test. Infrared studies of 11. R. Jayawardhana, S. Mohanty, G. Basri, Astrophys. J. The mounting evidence thus points to a even younger “proto-brown dwarfs,” which 578,L141 (2002). similar infancy for Sun-like stars and brown are still embedded in a dusty womb, may 12. R. Jayawardhana, S. Mohanty, G. Basri, Astrophys. J. 592, 282 (2003). dwarfs. Does this mean that the two kinds also provide clues to their origin. 13. J. Muzerolle et al., Astrophys. J. 592, 266 (2003). of objects are born in the same way? Many 14. S. Mohanty, R. Jayawardhana, D. Barrado y Navascués, observers tend to think so (7–12), but it References Astrophys. J. 593, L109 (2003). may be too early to rule out the ejection 1. G. Basri, Mercury 32, 27 (2003). 15. M. Fernández, F. Comerón, Astron. Astrophys. 380, 2. K. Lodders, Science 303, 323 (2004). 264 (2001). scenario for at least some brown dwarfs. 3. C. Low, D. Lynden-Bell, Mon. Not. R. Astron. Soc. 176, 16. D. Barrado y Navascués, S. Mohanty, R. Jayawardhana, Far-infrared observations with the Spitzer 367 (1976). Astrophys. J., in press.

ASTRONOMY lish a firm reference frame for the spectral classification of L and T dwarfs. Brown Dwarfs—Faint at Heart, Such observations represent major progress, because small sizes (roughly the radius of Jupiter) and low masses hamper Rich in Chemistry the detection of brown dwarfs. Their mass- es only reach up to ~7% that of the Sun (for Katharina Lodders comparison, Jupiter’s mass is ~0.1%), not enough to initiate and sustain the hydrogen

decade ago, brown dwarfs were not to those of giant planets, but are much burning that powers real stars. Brown on June 8, 2009 much more than a theoretical curios- more massive. Brown dwarfs are further dwarfs may burn deuterium if they exceed Aity in astronomy textbooks. It was divided into subtypes from zero for the 13 Jupiter masses. However, the energy re- unclear whether such objects, with masses hottest (L0, T0) to eight for the coolest (L8, leased by this deuterium burning is a small and temperatures between the giant planets T8), depending on whether certain spectral fire compared to the inferno of hydrogen and the coolest known dwarf stars, even features assumed to be a proxy of temper- burning in stars and lasts less than 100 mil- existed. Today, the problem is how to tell ature are present. Today, ~250 L dwarfs lion years for the most massive brown all the different low-mass objects apart. In and ~50 T dwarfs are known (9). dwarfs. In contrast, hydrogen can burn for a recent paper in Astrophysical Journal, Initially, subtyping of L dwarfs was several billion years in dwarf stars (10).

McLean et al. (1) propose a unified classi- based on red optical spectra, whereas T Much of the energy released by a brown www.sciencemag.org fication scheme for brown dwarfs on the dwarfs were sorted by near-infrared spectral dwarf over its lifetime is from gravitation- basis of near-infrared spectra. The scheme features (5–8). McLean et al. (1) have now al energy gained during its formation and also provides insights into the chemistry of advanced a unified classification scheme contraction. A brown dwarf’s main fate is these cool, dense objects. [For a discussion for L and T dwarfs based on ~50 objects an- to sit and cool in space. of brown dwarf origins, see (2).] alyzed with the Keck II Near-Infrared Deprived of a nuclear engine, brown The first brown dwarf, prosaically Spectrometer. They have used the high- dwarfs never exceed ~3000 K near their sur- called Gl229 B, was discovered in 1995 (3, quality near-infrared spectra to categorize faces. The more a brown dwarf cools, the

4). It was clearly substellar, sharing more brown dwarfs by the relative strengths of the less it is visible at optical wavelengths. M Downloaded from characteristics with giant planets like atomic lines of Na, K, Fe, Ca, Al, and Mg dwarf stars emit most strongly at red wave- Jupiter than with red M dwarfs, the coolest and bands of water, carbon monoxide, lengths (~0.75 µm), but maximum emis- and lowest mass stars known at the time. methane, and FeH. The observations estab- sions of the cooler L dwarfs (1200 to 2000 Many more brown dwarfs were discovered in the late 1990s thanks to large-scale in- frared sky searches [Two Micron All Sky NH3 CH4 gas CO gas CO gas NH4HS Survey (2MASS), Deep Survey of the Perovskite Corundum H2O KCl Southern Sky (DENIS), and Sloan Digital Mg-silicates CH4 gas CH gas 4 Iron metal liquid CO gas Sky Survey (SDSS)]. CsCl LiF RbCl Li2S Brown dwarfs fall in two spectral class- Na2S KCl CO gas es, L and T (5–8). L dwarfs, which are closer to M dwarfs than to giant planets in LiF CO gas Li2S Perovskite Corundum spectral appearance, include the lightest re- Na2S Mg-silicates al stars and the heaviest substellar objects. CO gas Iron metal liquid T dwarfs have spectra that are more similar Mg-silicates Deeper Iron metal liquid Perovskite Corundum Hotter CO gas CO gas Denser Perovskite Corundum The author is at the Planetary Chemistry Laboratory, Jupiter T dwarfs L dwarfs L to M dwarf transition Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA. A cloudy picture. Cloud layers for Jupiter, T dwarfs, L dwarfs, and objects near the transition from E-mail: [email protected] L to M dwarfs. The layers are progressively stripped off as the temperature of the object increases. www.sciencemag.org SCIENCE VOL 303 16 JANUARY 2004 323 Thus Not all Jupiters are Jupiter

Clouds depend on Color and albedo are BOTH internal heat functions of type and flow (mass, age) and depth of clouds. incident flux. Thus Not all Jupiters are Jupiter

Clouds depend on Color and albedo are BOTH internal heat functions of type and flow (mass, age) and depth of clouds. incident flux. Thus Not all Jupiters are Jupiter

Clouds depend on Color and albedo are BOTH internal heat functions of type and flow (mass, age) and depth of clouds. incident flux. Thus Not all Jupiters are Jupiter

Clouds depend on Color and albedo are BOTH internal heat functions of type and flow (mass, age) and depth of clouds. incident flux.

photochemistry Marley+ (1999)

Cahoy+ (2010)

Sudarsky+ (2000) Marley+ (1999)

Cahoy+ (2010)

Sudarsky+ (2000) HD 87883 b NH3 CH4 HD 39091 b 10.0 HD 219077 b Ups And d

HD 142 c H2O alkali 14 Her b 55 Cnc d HD 62509 b HD 217107 c Favorable RV 47 Uma d

) Gam Cep b J Mu Ara e Planets for HD 190360 b Eps Eri b

) (M HD 154345 b Direct i 1.0 Ups And e HD 134987 c Imaging by M sin( GJ 832 b 47 Uma c WFIRST HD 99492 c

0.1 HD 192310 c

100 200 300 400 500 600 Teff (K) Marley+ 2014 HD 87883 b NH3 CH4 HD 39091 b 10.0 HD 219077 b Ups And d

HD 142 c H2O alkali 14 Her b 55 Cnc d HD 62509 b HD 217107 c Favorable RV 47 Uma d

) Gam Cep b J Mu Ara e Planets for HD 190360 b Eps Eri b

) (M HD 154345 b Direct i 1.0 Ups And e HD 134987 c Imaging by M sin( GJ 832 b 47 Uma c WFIRST HD 99492 c LUVOIR

0.1 HD 192310 c

100 200 300 400 500 600 Teff (K) Marley+ 2014 What do we Want to Know? Owen et al. (1999) LUVOIR

Owen et al. (1999) Kreidberg+ 2014 Hatzes & Rauer (2015) Super-Earths to ! sub-Neptunes

Hatzes & Rauer (2015) Clouds & Variability

• Clouds reflect atmospheric temperature

• Clouds set continuum flux level for measuring bands

• Training ground for interpreting terrestrial planets

• Variability hints at complex atmospheric dynamics

Neptune Photochemical Hazes

Zahnle+ (2016) What about Transit Spectroscopy?

GJ 1214b

Upper vs. deep atmosphere ! Atmospheric column is more thoroughly measured by imaging than by transits ! Model spectra by Caroline Morley

ExoPAG 11 How do we Find Out? “Baines Diagram” “Baines” diagram for Uranus

Gas

Rayleigh Wavelength (micron) “Baines” diagram for Uranus

Gas

Rayleigh Wavelength (micron) “Baines” diagram for Uranus

Gas

Rayleigh Wavelength (micron) “Baines” diagram for Uranus

Gas

Rayleigh Wavelength (micron) Weak methane (727 nm)

Continuum (751 nm)

Air Force Advanced Electro-Optical System (AEOS) 3.6-m telescope on Maui High Clouds on Uranus

H

K’

Hammel et al. Shoemaker-Levy 9 Impact on Jupiter seen with Hubble Uranus with Hubble/STIS

Methane depletion in both polar regions of Uranus inferred from HST/STIS and Keck/NIRC2 observations ! L. A. Sromovsky+ (2014) H2 Opacity Also Important in Ice Giants

Sromovsky et al. (2014) Classic 1979 paper on deriving giant planet abundances

Step 1: Cloud Model

First use H2 quadrupole lines to constrain cloud. Strong CH4 Weak CH 4 clouds constrains bands Reflectivity in 2 Step 2: CH4 Abundance

Cloud model plus equivalent widths of other methane bands gives CH4 abundance Step 3: Consistency Checks

• Utilize entire spectrum to check derived abundance

• Further constrain high altitude hazes and NH3 abundances

• All by bootstrapping using multiple CH4 bands plus continuum Accuracy? Accuracy? Issues for Giant Exoplanets

• Noisier data

• Little to no a priori knowledge (gravity, radius, gross atmospheric structure, orbital phase, etc.)

• Same issues will be faced by terrestrial planet studies (giants just get there first) MCMC Retrievals of Cool Giants Example: Jupiter 9 parameters

fCH4, log g Results

bright NH3 ! cloud Results

bright NH3 ! cloud Results

0 wbar 1.0 bright NH3 ! dark haze cloud Results

0 wbar 1.0 bright NH3 ! dark haze cloud Results

0 wbar 1.0 -2.4 -0.8 bright NH3 ! dark haze log fCH4 cloud Results

0 wbar 1.0 -2.4 -0.8 bright NH3 ! dark haze log fCH4 cloud Results

0 wbar 1.0 -2.4 -0.8 bright NH3 ! dark haze log fCH4 cloud Retrieval Assumed Unconstrained Gravity

25 MJup

6 MJup

1 MJup

-2.4 -0.8 log fCH4 Higher gravity implies smaller column abundance above cloud and more CH4 However…

• Astrometry of RV planets will resolve sin i uncertainty and constrain masses

• Need about 3 visits for mass good to about 20%

• Along with radius constraints should provide much tighter log g range Mass constraint combines with multiple radius constraints ! Assume gravity known to within 4x !

Correct CH4 retrieval, but no gravity improvement Mass constraint combines with multiple radius constraints ! Assume gravity known to within 4x !

Correct CH4 retrieval, but no gravity improvement

Complications…. Phase Behavior

Lambertian

Phase angle (degrees) Mayorga+ (2016) Phase Angle — Planet Radius Degeneracy Conclusions

• Decades of experience exist for extracting atmospheric composition for Solar System giants

• Both methane AND continuum samples are important for determining altitudes and compositions

• Observing more than one methane band significantly improves knowledge of atmospheric vertical structure

• Cloud heights, absorber abundances can be accurately derived from visible spectra for R > 70 Won’t WFIRST Do All This?

• Coronagraph Instrument is technology demonstrator for high contrast imaging

• Only 2.4-m telescope, 1 year for coronagraph

• Very Limited targets w/spectra only 600 to 900nm

• No NH3, likely no H2O, weak constraints on hazes LUVOIR Advantages

• Spectra from blue through near- IR

• haze absorption

• more continuum & CH4 bands

plus H2O, NH3, Na, K Sudarsky+ (2000)

• Very high SNR for “free” in terrestrial planet systems

• Time resolved spectra Role for LUVOIR

• Characterize all possible planets

• provides context for habitable planets

• need to understand systems holistically incl. near misses

• Nature of super Earths/sub-Neptunes

• Giant planets

• easier, outstanding spectroscopy targets (OWA requirement)

• laboratories for clouds, composition (CH4, H2O, NH3, Na, K) photochemistry, formation, stellar influence, etc. Polarization? Backup Polarization of Venus Dollfus & Coffeen 0.34um (1970)

0.40um

0.53um

1.05um Polarization of Venus Dollfus & Coffeen 0.34um (1970)

0.40um

0.53um

1.05um Baker et al. (1975) Jupiter R=100

To retrieve abundances need to constrain both cloud height (absorbing gas column) and band depths. For this need multiple bands plus

Geometric Albedo Geometric continuum.

Wavelength (um) Jupiter R=50 Jupiter R=25 Jupiter R=10 Ice Giant R=100 Ice Giant R=50 Ice Giant R=25 Ice Giant R=10