Poten&al for Characteriza&on of Transi&ng Planets with JWST
Nick Cowan (Northwestern)
Study Analysis Group 10 (SAG-‐X) 1. What is the full diversity of planet proper&es needed
to characterize and understand the climate of short-‐period exoplanets?
2. Which measurement suites and how much observing &me are needed to characterize the climate of transi&ng planets?
3. Will JWST be able to characterize the atmospheres of transi8ng terrestrial planets?
4. Which cri8cal measurements will be too expensive or inaccessible to JWST, and can these be obtained with planned observatories?
SAG-‐X Par&cipants (so far) Daniel Angerhausen (RPI), Natasha Batalha (Penn State), Adrian Belu (Bordeaux), Knicole Colon (Lehigh), Bill Danchi (Goddard), Pieter Deroo (JPL), Jonathan Fortney (UCSC), ScoV Gaudi (Ohio State), Tom Greene (Ames), MaV Greenhouse (Goddard), Joe Harrington (UCF), Lisa Kaltenegger (MPIA), Nikole Lewis (MIT), Chuck Lillie (Lillie Consul&ng), Mercedes Lopez-‐Morales (CfA), Avi Mandell (Goddard), Emily Rauscher (Princeton), Aki Roberge (Goddard), Franck Selsis (Bordeaux), Kevin Stevenson (Chicago), Mark Swain (JPL)
1D Climate Cartoon He
ight
Temperature Tsurf
Tropopause
Tstrat
Γ Troposphere
Stratosphere
Thermal Emission Probes Near Tropopause
Reflected Light Probes Near Surface
1D Climate Cartoon
Temperature
Height
Increase Insola&on and/or Decrease Albedo
1D Climate Cartoon
Temperature
Height
Increase Longwave Opacity
1D Climate Cartoon
Temperature
Height
Decrease Specific Heat Capacity
Advec&on
2D Climate Cartoon (eg: height + la&tude)
Temperature
Height
To learn from exoplanets, we need to measure: • Planetary Albedo • Albedo Gradients • Emiang Temperature • Temperature Gradients (ver&cal and horizontal)
Unfortunately we don’t have robust predic&ve models for: • Clouds • Atmospheric Loss • Photochemistry • Geochemical Cycling • Wind Veloci&es
Predic&ng vs Measuring Planetary Climate
Model Inputs • Insola&on • Eccentricity • Obliquity • Surface Albedo • Greenhouse Gases • Specific Heat Capacity • Surface Gravity • Surface Pressure • Thermal Iner&a
Model Outputs • Emiang Temperature • Temperature Gradients • Diurnal Response • Seasonal Response • Cloudiness • Surface Temperature • Precipita&on
Transit Phase Varia&ons
Archetypal Short-‐Period Planets
Hot Earth (CoRoT-‐7b, Kepler 10b, α Cen Bb) Temperate Super-‐Earth (HD 85512 b, GJ 163 c) Warm Neptune (GJ 1214b, GJ 436b) Hot Jupiter (HD 209458b, HD 189733b, WASP-‐12b)
Transit
Thermal Light Curve Brightness
Time
100%
99% Transit
Transit Depth = (Rp/R*)2
Some Transit Depths
Hot Jupiter: 8.8E-‐3
Hot Earth: 7.3E-‐5
Temperate Super-‐Earth: 7.3E-‐3
Warm Neptune: 2.7E-‐2
Thermal Light Curve Brightness
Time
100%
99% Transit
Transit depth is different at different wavelengths
Annulus/Stellar Area = 2RpH/R*2 (where scale height H = kBT/μg)
Some Transit Spectral Features
Hot Jupiter: 1.2E-‐4
Hot Earth: 2.0E-‐6
Temperate Super-‐Earth: 6.5E-‐6
Warm Neptune: 2.4E-‐4
Eclipse
Thermal Light Curve
Brightness
Time
100.3%
99% Transit
Eclipse 100%
Eclipse Depth ≈ (Rp/R*)2 (Tday/T*)
Star + Planet Star
Some Eclipse Depths
Hot Jupiter: 4.0E-‐3
Hot Earth: 3.3E-‐5
Temperate Super-‐Earth: 7.0E-‐4
Warm Neptune: 8.1E-‐3
Thermal Light Curve
Brightness
Time
100.3%
99%
Transit 100%
Star + Planet Star
Eclipse depth is different at different wavelengths
Eclipse Spectrum ≈ (Rp/R*)2 (Tsurf -‐ Ttrop)/T*
Thermal Phases
Thermal Light Curve
Brightness
Time
100%
Transit Eclipse
100.3%
Star + Planet Star
100.1%
Phase Amplitude ≈ (Rp/R*)2 (Tday -‐ Tnight)/T*
Eclipse Spectroscopy vs. Phase Varia&ons
• Differences in temperature – Ver&cal (33-‐200 K) – Zonal (60-‐2000 K)
• Spectroscopy has to achieve S/N with rela&vely narrow bandwidth (R>10)
• Phase varia&ons require long-‐term stability
Predic&ng vs Measuring Planetary Climate
Model Inputs • Insola&on • Eccentricity • Obliquity • Surface Albedo • Greenhouse Gases • Specific Heat Capacity • Surface Gravity • Surface Pressure • Thermal Iner&a
Model Outputs • Emiang Temperature • Temperature Gradients • Diurnal Response • Seasonal Response • Cloudiness • Surface Temperature • Precipita&on