Terrestrial Exoplanet Science with JWST
Victoria Meadows, Eddie Schwieterman, Giada Arney, Drake Deming,
Amit Misra, Benjamin Charnay, Ty Robinson, Antigona Segura, Shawn
Domagal-Goldman and the NAI Virtual Planetary Laboratory Team
The University of Washington, California Institute of Technology, Jet Propulsion Laboratory, Pennsylvania State
University, NASA Goddard Space Flight Center, University of Maryland, NASA Goddard Institute for Space Studies,
University of Chicago, Weber State University, Princeton University, NASA Ames Research Center, Stanford University,
Rice University, Washington University at Saint Louis, Yale University, Australian Center for Astrobiology, University of
Victoria, Laboratoire d’Astrophysique – Bordeaux
Terrestrial Exoplanet Science with JWST
• Comparative Planetology
– What are these things?
– How are super-Earths and mini-Neptune related to each
other, and to other planets in our Solar System?
– What can these planets tell us about planetary processes in
different physical and chemical regimes?
• The Search for Life Beyond the Solar System
M dwarf HZ planets are the most common in the Galaxy
– What are their characteristics?
– Are they habitable?
– Do they exhibit signs of life?
Observations: Transit, eclipses and phase curves
See talk by Julien de Wit
Cowan et al., 2015
What JWST Can Do for small exoplanets
• Potential first detailed studies of the composition of miniNeptune atmospheres.
–
Haze becomes transparent, maybe! See Caroline Morley’s talk.
• Best way to study planets orbiting M dwarfs
– M dwarfs are the most common planetary host star.
• M dwarf habitable planets are likely the most common habitable
worlds
– and have interesting “issues”!
• In particular JWST could provide
– relatively rapid surveys of the composition and atmospheric
structure of mini-Neptunes
– spectra and phase curves of a handful of hot Earths
– The first characterization of a HZ Earth
Challenges for Transmission Spectra
of Terrestrials
Refraction Limits Altitudes Probed
Transmission spectra are insensitive to the planetary surface
For every planet/star system there will be a maximum pressure (or minimum
altitude) that can be probed.
Larger angular extent of the star allows deeper probing of the atmosphere
• Probe deeper for planets in M dwarf habitable zones
Garcia-Muñoz et al., 2012; Misra, Meadows and Crisp., 2014; Bertremieux & Kaltenegger, 2013, 2014
Habitable terrestrials have dry stratospheres.
Exotic biosignatures need to reach the stratosphere
Altitude
Early Earth with a sulfur-dominated biosphere, orbiting an M dwarf.
Domagal-Goldman, Meadows et al., 2011
Haze can severely limit transmission spectra
GJ1214b: Not Solar composition
Not high mean molecular mass atmosphere
Conclusion: High-altitude cloud/haze
Kreidberg et al., 2014
M Dwarf Planets: Gravitational Effects
• Tidal Locking
– Circularization
– Climate effects
• Tidal Effects
– Tidal Habitable Zone
– Tidal Venuses
– Loss of magnetic field
M Dwarf Planets: Radiative Effects
• Spectrum of starlight
– Affects climate via changes to
atmospheric/surface absorption
– Photochemistry
• Stellar Activity
– Photochemistry
– Surface UV fluxes
• Extended Pre-Main Sequence
M Dwarf Planets May Make Their Own O2!
During the Pre-MS of M dwarfs
terrestrial planets can lose
several Earth oceans of water via
hydrodynamic escape during the
PMS phase of M dwarfs.
Luger & Barnes (2015)
Total Water Lost
Depending on
sinks, upof
on surface
the strength
to
several
hundreds
of bars ofof
surface
sinks,
several hundreds
photolytically-produced
O2 can
bars of photolytically-produced
potentially
build build
up up
in inthe
O2 can potentially
the
atmospheres of these planets.
& Barnes
(2015)
LugerLuger
& Barnes
(2014),
submitted
Atmospheric O2
Early Atmospheric Loss for M dwarf planets
This extra pre-MS luminosity can
last for up to a billion years and
could dessicate planets formed
in the habitable zone of low
mass stars within the first 100
Myr
THE PUNCHLINE: Planets orbiting
stars above a stellar mass of ~ 0.4
are less likely to experience this
phenomenon, especially towards
the outer edge of the HZ.
Contours are bars of O2 produced
by water photolysis and H escape
Luger and Barnes, 2015
Abundant O2 may not indicate habitability
1. H Escape from Thin N-Depleted Atmospheres
(Wordsworth & Pierrehumbert 2014)
2. Photochemical Production of O2/O3 (DomagalGoldman, Segura, Claire, Robinson, Meadows 2014)
3. O2-Dominated Post-Runaway Atmospheres
from XUV-driven H Loss (Luger & Barnes 2014)
4. CO2 Photolysis in Dessicated Atmospheres
(Gao, Hu, Robinson, Li, Yung, 2015 )
Mini-Neptunes
• What are these objects?
• How do they form and evolve?
– Orbital architecture, bulk density, atmospheric composition
• Atmospheric Physical Properties
– high precision thermal phase curves and spectra
– can be inverted to produce longitudinal T, composition maps
• How do we distinguish them from super-Earths?
JWST can learn about these objects in a single transit
or phase curve.
Should be able to do a survey of these objects to
explore characteristics as a function of size, semi-major
axis, etc.
Sub-Neptunes may exhibit many atmospheric compositions.
Hu & Seager, 2014
JWST may get us beyond “the flat zone” for mini-Neptunes
GJ1214b
LMDZ 3D GCM can loft r=0.5μm
cloud particles to recreate the flat
HST spectra. Resultant haze
Should be optically thin at λ > 3μm
A single transit could detect molecules
Charnay, Meadows, Misra, Leconte, Arney (2015) in press
Caroline may not agree with us! Looking forward to her talk…
Thermal Phase Curves May Reveal Metallicity
Day-night T contrasts are strongly
dependent on metallicity.
Could be observed in one full
phase curve with JWST @ 6-8um
Charnay, Meadows, Misra, Leconte, Arney (2015) in press
Menou et al., (2012) also studied this effect for a cloud-free GJ1214b with gray opacities.
Hot Earths
• Do they have atmospheres
• What is their atmospheric composition and physical
properties?
• Atmospheric Physical Properties
– high precision thermal phase curves and spectra
– can be inverted to produce longitudinal T, composition maps
• Testbeds for terrestrial atmospheric evolution.
• Could serve as test cases for abiotic production of O2
Raymond, Quinn & Lunine 2004
Inner planets may form wet or dry
•Water-poor inner planets are often, but not always, formed
•Initial composition depends sensitively on the Jovians
Initially wet planets may exhibit abiotic O2
Atmospheric O2
If a hot Earth has abundant O2 then we know that the abiotic
formation mechanism is viable, which may be a concern
for false positive O2 in the HZ
Massive O2 atmospheres may have O4 features
Transit Depth (ppm)
Sun
O3
O2-B
O3
O2-A
O4
O4
GJ 876
M4V
O3
O3 O2-B
O2-A
H2O
O4
H 2O O
4
H 2O
Wavelength (µm) Schwieterman et al., in prep
Initially “Dry” Planets may become Venus-like
…and Venus is the popcorn of the Solar System
Venus lost at least the equivalent of a global ocean 3m deep
GJ1132 b as a Super-Venus
CO2
CO2
CO2
CO2
Giada Arney
Could we detect geological activity?
Misra et al., 2015
If multiple transits can be binned over (one per month for 4 years), and a large fraction of the
wavelength range binned, we find that it may be possible to detect (S/N ~ 7) a Pinatubo-sized
eruption with JWST for an Earth-analog planet orbiting an M5V.
Habitable Zone Terrestrials
• What are their characteristics?
• Are they habitable?
• Do they show signs of life?
Transit Depth [ppm]
Modern Earth orbiting an M5V
CO2
CO2
O3
CO2
N2O
O3
O3
O2
CO2
H2O
CH4
CH4
H 2O
H2O
O4
O4
CH4
N2O
CO2
Wavelength [µm]
Features at 2-30 ppm. Water vapor seen at the few ppm level.
Transmission model (includes refraction) from Misra et al., (2014)
Model is cloud-free, however continuum corresponds to 8km above the planetary
surface, likely above any actual cloud deck.
Segura et al., 2003, 2005
Atmospheric Chemistry Around M Dwarfs
CH4
fs = 9.5 x 1014 g/yr,
except M5V
N2O
fs = 7.3 x 1012 g/yr
more
•Earth-like planets around cooler stars show
enhanced biosignature abundances (Segura
et al., 2003, 2005)
– M stars less effective at O3 photolysis.
•Enhancements in biosignatures, (including
O3), are also seen when an Earth-like planet
is moved towards the outer edge of its
habitable zone (Grenfell et al., 2006, 2007)
CH3Cl
fs = 1.3 x 1013 g/yr
Transit Depth [ppm]
Photochemically Self-Consistent Earth Orbiting an M3.5Ve
CO2
Features 2-6ppm!
CO2
CH4
CH4
O3
CH4 CO2
O3 O2
CH4
N2O
CO2
O3
N2 O
N2O
O4
O4
10km altitude
Wavelength [µm]
E. Schwieterman
Spectrum of self-consistent Earth around an M3.5V (Rsun = ) from Segura
et al. (2005). Transmission model (includes refraction) from Misra et al.,(2014)
Model is cloud-free, however the deepest altitude reached is10km, likely
above any actual cloud deck. This also explains the lack of water vapor.
NIRISS Spectrum of M3.5V Earth
10 transits/65 hrs
Rebinned 2048 -> 32 columns
CH4
CH4
CO2
CH4
Drake Deming
NIRSPEC Spectrum of M Dwarf Earth
10 transits/65 hrs
CH4
CO2
Stellar intensity dropping
Thermal rising
Drake Deming
O4 in Transit Transmission
JWST may be able to
detect (SNR > 3) the
1.06um O4 and 1.27um O2
features for an Earth-like
planet orbiting an M5 dwarf
5pc away.
IF we can get every transit
in 5 years of the mission or
IF the sensitivity is better
than expected!
The oxygen A band would
likely not be detectable
(1.1-sigma), even in the
cloud-free case.
Misra, Meadows, Crisp, Claire (2014)
Transit Depth [ppm]
Photochemically “self-consistent-ish” Earth orbiting M5V
Features 2-25ppm!
CO2
CO2
CH4
CH4
CH4
O3
O3
CO2
N2O
O3
O2
CO2
H2O
O4
O4
N2O
Wavelength [µm]
H2O
N2 O
8km altitude
Wavelength [µm]
E. Schwieterman
Planet from Segura et al. (2005; Forced by M3.5V). Geometry of M5V.
Transmission model (includes refraction) from Misra et al., (2014).
High abundances of methane swamp water vapor.
O2 at 5ppm, O3 slope 10ppm.
Model is cloud-free, however the deepest altitude reached is 8km, likely
above any significant cloud deck. This also explains the lack of water vapor.
Altitude
Possible Alternative Biosignatures
• Transmission
Spectrum of Early
Earth Orbiting an
M Dwarf
Domagal-Goldman, Meadows et al., 2011
Transmission Spectrum of Early Earth with sulfur-dominated biosphere orbiting AD Leo
Archean Earth Orbiting an M Dwarf
Alternative Earth: AD Leo 30 × Sorg
Transit Depth [ppm]
CO2
Ethane is a biosignature CO2
in this context
C 2H 6
CO2 CH4
CH4
C 2H 6
CH4
CH4
CO2
CO2
Wavelength [µm]
E. Schwieterman
• Self-consistent early Earth (anoxic atmosphere/sulfur biosphere) around
M3.5V from Domagal-Goldman et al., (2011)
• Model is cloud and haze-free, and the deepest altitude reached is 10km, likely
above any actual cloud deck.
• Distinctive sulfur gases in the troposphere are not seen in the spectrum.
Hazy Archean Earth orbiting GJ 1132b
Hydrocarbon haze
CH4
CH4 CH4
CH4
CH4
CO2
CO2
CO2
CH4
HC haze
CO2
Hazy Archean Earth
Full spectrum
Some Thoughts on Target Selection
How should we pick the right planet to study?
✔
TESS will most likely find JWST targets
TESS
• Predictions suggest 48 TESS planets lie within or near the HZ
• 2-7 of these planets will have host stars brighter than KS=9
(Sullivan et al., 2015)
The Habitability Index
The “Problem”
(P, d,D,R∗,M∗, Teff ) →
(L∗, a, e, A, S).
Use observables
from a transit to
constrain and assess
the fraction of
possible parameter
combinations that
would produce
habitable climates.
Barnes, Meadows & Evans, 2015
Habitability Index for TESS Planets
From Barnes, Meadows & Evans,
(2015)
Based on a the Sullivan et al.
(2015) study to predict the
exoplanet yield from TESS.
Summary
• Warm mini-Neptunes (e.g. GJ1214b) should be straightforward targets for
JWST, which has the potential to characterize their cloud and atmospheric
composition using transmission spectra, secondary eclipse and phase curve
measurements.
• JWST will be our first chance to characterize terrestrial planets, including
those in the habitable zone of their parent star.
• For HZ planets observations will require ppm sensitivity
– Refraction may limit observations to the stratospheres
– Water and tropospheric biosignatures may be difficult to detect.
• Transit observations coadded over several years may be necessary.
– Systematic noise sources will need to be characterized and “dealt with”.
• Target selection will be important, as features for these targets will take
many transits to appear.
PI: Victoria Meadows (UW)
With Thanks To…
Eric Agol (UW)
Rika Anderson (NAI-NPP/WHOI)
John Armstrong (Weber State)
Jeremy Bailey (UNSW)
Giada Arney (UW)
Rory Barnes (UW)
John Baross (UW)
Cecelia Bitz (UW)
Bob Blankenship (WUStL)
Linda Brown (NASA-JPL/Caltech)
Roger Buick (UW)
David Catling (UW)
Benjamin Charnay (NAI-NPP/UW)
Mark Claire (U. St. Andrews)
David Crisp (NASA-JPL/Caltech)
Pan Conrad (NASA-GSFC)
Russell Deitrick (UW)
L. Drake Deming (U. Maryland)
Feng Ding (U. Chicago)
Shawn Domagal-Goldman (NASA-GSFC)
Peter Driscoll (CIW)
Peter Gao (Caltech)
Colin Goldblatt (U. Victoria)
Chester (Sonny) Harman (PSU)
Suzanne Hawley (UW)
Tori Hoehler (NASA-Ames)
Jim Kasting (PSU)
Nancy Kiang (NASA-GISS)
Ravi Kopparapu (PSU)
Monika Kress (SJSU)
Andrew Lincowski (UW)
Rodrigo Luger (UW)
Jacob Lustig-Yaeger (UW)
Amit Misra (UW)
Niki Parenteau (NASA-Ames)
Ray Pierrehumbert (U. Chicago)
Tom Quinn (UW)
Sean Raymond (Lab. Astrophysique de Bordeaux)
Tyler Robinson (Sagan Fellow – UC Santa Cruz)
Eddie Schwieterman (UW)
Antigona Segura (UNAM)
Janet Seifert (Rice U.)
Holly Sheets (U. Maryland)
Aomawa Shields (NSF/UCLA/Harvard)
Eva Stüeken (UW)
Lucianne Walkowicz (Adler Planetarium)
Robin Wordsworth (Harvard)
Yuk Yung (Caltech)
Kevin Zahnle (NASA-Ames)
PI: Victoria Meadows (UW)
With Thanks To…
Eric Agol (UW)
Rika Anderson (NAI-NPP/WHOI)
John Armstrong (Weber State)
Jeremy Bailey (UNSW)
Giada Arney (UW)
Rory Barnes (UW)
John Baross (UW)
Cecelia Bitz (UW)
Bob Blankenship (WUStL)
Linda Brown (NASA-JPL/Caltech)
Roger Buick (UW)
David Catling (UW)
Benjamin Charnay (NAI-NPP/UW)
Mark Claire (U. St. Andrews)
David Crisp (NASA-JPL/Caltech)
Pan Conrad (NASA-GSFC)
Russell Deitrick (UW)
L. Drake Deming (U. Maryland)
Feng Ding (U. Chicago)
Shawn Domagal-Goldman (NASA-GSFC)
Peter Driscoll (CIW)
Peter Gao (Caltech)
Colin Goldblatt (U. Victoria)
Chester (Sonny) Harman (PSU)
Suzanne Hawley (UW)
Tori Hoehler (NASA-Ames)
Jim Kasting (PSU)
Nancy Kiang (NASA-GISS)
Ravi Kopparapu (PSU)
Monika Kress (SJSU)
Andrew Lincowski (UW)
Rodrigo Luger (UW)
Jacob Lustig-Yaeger (UW)
Amit Misra (UW)
Niki Parenteau (NASA-Ames)
Ray Pierrehumbert (U. Chicago)
Tom Quinn (UW)
Sean Raymond (Lab. Astrophysique de Bordeaux)
Tyler Robinson (Sagan Fellow – UC Santa Cruz)
Eddie Schwieterman (UW)
Antigona Segura (UNAM)
Janet Seifert (Rice U.)
Holly Sheets (U. Maryland)
Aomawa Shields (NSF/UCLA/Harvard)
Eva Stüeken (UW)
Lucianne Walkowicz (Adler Planetarium)
Robin Wordsworth (Harvard)
Yuk Yung (Caltech)
Kevin Zahnle (NASA-Ames)
CO2
CO2
CH4
O3
CH4
CH4 CO2
O3
O2
N2O
CO2
CH4
O3
N2O
N2O
O4
O4
Robinson, Meadows, & Crisp (2010)
http://vpl.astro.washington.edu/spectra/planetary/earth_orbit.htm
Glint
Predictions
From The VPL Earth Model
nm
l = 600-800
Venus in Transit
Giada Arney
Venus would exhibit many of these problems: orbiting a G dwarf and with a high haze.
LCROSS Observations of Earth Glint
Images of the Earth taken with the
LCROSS NIR2 camera (0.9-1.7μm)
and MIR1 camera (6-10μm)
Robinson et al., 2014
LCROSS Data Confirm Glint Predictions
This phase (129°) would
require 77mas separation
for an Earth twin at 10pc
Robinson et al., 2014
Robinson et al., 11:30am Today in Salon A1!
Detecting Glint for an Exo-Earth
For Exo-C
α Cen A super-Earth (1.7 RE)
R = λ/Δλ = 10
SNR ~ 10
simulated data
Δt = 10 days
IWA = < 460mas
low-res model
hi-res model
0.6-0.9μm optimal for photometry
to look for oceans (reduced Rayleigh)
but does JWST have the sensitivity to
do this? Nick doesn’t think so!
Ty Robinson
Meadows, Robinson, Misra et al., 2015