VOSS 2025: JWST Exoplanets

June 2025

Exoplanet trends and the future

T Greene

VOSS 2025

Credit: Kammerer, Pueyo (STScI), Juanola Parramon, Stark (GSFC)

Lecture topics

• Summary and trends of JWST & HST studies
• JWST exoplanet status
• M star imaging survey (Bogat+)
• Gas giants, ice giants, mini-Neptunes, rocky planets
• MANATEE science & data lessons learned
• Rising research areas
• Population comparisons
• Linking compositions to disks
• Future missions
• Roman, ARIEL, ELTs, Habitable Worlds Observatory

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JWST spends a lot of time on exoplanets!

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Espinoza & Perrin (2025)

JWST exoplanet observations

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Espinoza & Perrin (2025)

M dwarf imaging survey (Bogat+ 2025)

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NIRCam coronagraphic observations in F356W + F444W filters

M dwarf imaging survey (Bogat+ 2025)

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NIRCam coronagraphic observations in F444W filter

M dwarf imaging survey (Bogat+ 2025)

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NIRCam coronagraphic observations in F444W filter

M dwarf imaging survey (Bogat+ 2025)

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F444W filter

Widely-separated planets are not common around nearby M dwarfs

Fu+ (2025) Ice & gas giant comparison

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• Study H₂O, CH₄, SO₂, CO, CO₂ trends

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• SO₂ is preferentially found in low mass (< 100 Me) and cooler (T < 1200 K) planets

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• Metallicity is inversely correlated with mass

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• Most have super-solar metallicity and low C/O < 0.7

Fu+ (2025) ice & gas giant comparison

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Brande+ (2024) cloudy/hazy HST study

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Sample suggests minimum clouds/hazes at T ~ 600 K, but not true for all planets

(i.e., GJ 1214 b)

MANATEE transiting exoplanet science l�essons

• Panchromatic spectra are key for understanding atmospheric states and compositions but are often difficult to interpret
• Low CH4 abundances in exoplanet atmospheres can be understood in terms of vertical mixing, but we don't understand what causes different amounts of mixing
• Is installation involved?
• Clouds do more than mute transmission spectra:
• Can cause dayside inhomogeneities (WASP-96 b)
• Can cool planets and mute emission features (GJ 436 b, WASP-96 b)
• Compositions are sometimes straightforward (GJ 436 b, W-96 b) and sometimes not (WASP-107 b). More data often makes it harder to determine compositions!
• Planetary atmospheres can reveal information about interiors (WASP-107 b T_int)
• Neptunes and sub-Neptunes have diverse compositions
• GJ 3470 b has [M/H] like our Solar System planets, GJ 1214 b probably does not
• Dynamical evolution and atmospheric stripping may be involved
• Terrestrial planets interior to habitable zones of M stars have difficulty retaining atmospheres (TRAPPIST-1 b/c)

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MANATEE data analysis lessons learned

• Discard the first 0 -–~30 minutes of data in a time series and fit the low-order detector charge decay (time and fit depend on detector)
• Use the same system parameters and limb-darkening approach in all data sets and wavelength ranges for a given planet. Avoid free limb darkening at every wavelength; that fits systematic noise and is not astrophysically realistic
• Bin data to desired spectral resolution before fitting light curves (somewhat of a religious issue, but it works for us)
• Examine the Allan variance plot for how well noise decreases with binned integration time. Apply Gaussian processes in the time domain to fit the spectral data
• Allow transit depth offsets when stitching together multiple observations taken at different wavelengths. This is expected due to imperfect linearity or other corrections
• Have modelers assess the 'final' data sets for implausible consequences or physical/chemical inconsistencies between multiple reductions that do or do not look similar by eye
• Have a great team – go MANATEES!

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Next Steps: Compare populations to probe formation

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• How similar are the compositions of Hot, warm, and cold Jupiters?
• Are they consistent with formation in similar disk locations & accretion + scattering?

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Next Steps: Planet formation and system evolution

• Constrain planet formation better by coupling atmospheric compositions to disk models
• Statistical assessment of C/O, [M/H], and other ratios in multiple planets with disk model grids

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• Parameter exploration of disk models with radiative transfer and chemistry in Bayesian framework (Mollière+ 2022; Majumdar+)

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• Advance understanding of exoplanet interiors and heating sources with further atmospheric characterization

– Statistical Studies of disequilibrium, T_int, eccentricity, other parameters in multiple systems

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• Constrain formation and evolution of terrestrial planets

– Do any rocky/terrestrial planets in or near the habitable zones of M stars have atmospheres (new JWST Rocky Worlds DDT program)

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Future progress in exoplanet atmospheres

• Transits: SNR ~ D due to stellar photon noise
• JWST: continued characterization through 2030+:
• Mini-Neptune and Super-Earth compositions, panchromatic gas giant spectra (formation and migration), TRAPPIST-1 e habitable zone Earth-mass planet
• More new discoveries: TESS, PLATO (2026), ground-based precision radial velocities
• ARIEL: statistical characterizations (2029 launch)
• Direct imaging: Eliminate star to reduce noise
• Roman Space Telescope coronagraph (2027 launch)
• E-ELT: M star planets (maybe 2035)

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Transit missions flying by 2030

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New transiting planet discoveries

• TESS (now) and PLATO (2026) will search up to 10⁶ stars for transiting planets
• Precision radial velocity measurements with ESPRESSO, Keck Planet Finder, Express, Keck HISPEC (IR), NEID will measure masses:
• Mass, radius, density, orbits
• Ariel (2029) will observe the visible to near-IR spectra of ~1000 exoplanets for statistical population characterization (lower precision than JWST)

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NASA mission & technology timeline

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Toward the “Pale Blue Dot”

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WIFRST will lay the foundation for a future flagship direct imaging mission capable of detection and characterization of Earth-like planets.

Microlensing Survey

High Contrast Imaging

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• Inventory the outer parts of planetary systems, potentially the source of the water for habitable planets.
• Quantify the frequency of solar systems like our own.
• Confirm and improve Kepler’s estimate of the frequency of potentially habitable planets.
• When combined with Kepler, provide statistical constraints on the densities and heavy atmospheres of potentially habitable planets.

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• Provide the first direct images of planets around our nearest neighbors similar to our own giant planets.
• Provide important insights about the physics of planetary atmospheres through comparative planetology.
• Assay the population of massive debris disks that will serve as sources of noise and confusion for a flagship mission.
• Develop crucial technologies for a future mission, and provide practical demonstration of these technologies in flight.

Science and technology foundation for the New Worlds Mission.

Courtesy of Jim Kasting.

Simulated WFIRST-AFTA coronagraph image of the 47 UMa planetary system

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Exoplanet Surveys�Kepler & WFIRST

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M. Penny (OSU)

DIRECT IMAGING IN REFLECTED LIGHT (THE FUTURE)

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Direct imaging exoplanet reflection geometry

• Light from the host star enters the planet’s atmosphere and is scattered (i.e., Rayleigh) or reflected by clouds toward the observer
• Same physics and geometry as looking at Solar System planets from Earth
• This can sample a large atmospheric column if clouds are at high pressures (deep in the atmosphere)

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Giant spectra: molecules, clouds, hazes

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Adapted from M. Marley

model

obsv

observed but not in model

Giant Planet Reflected Spectra

• Geometric albedo spectra (Karkoschka 1994) for the solar system giant planets.

• All four planets are darker at all wavelengths than perfect Rayleigh or Lambert scattering spheres.

• Jupiter contrast relative to Sun is 1E-9. This gets better in the mid-IR where thermal emission is up and the star is falling off (JWST imaging sweet spot)

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Courtesy of M. Marley & PECO study

Giant planet albedo with stellar distance

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• Strong CH4 absorption in cool giants > 2 AU from Sun: DETECTABLE!

• Clouds disappear and albedo drops as Jupiter moves toward the Sun and heats up.

• Absorption from Alkalis Na and K dominate in visible (Cahoy, Marley & Fortney 2010)

Simulated Roman CGI images

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Current best estimate of Roman CGI:

First: circumstellar disk;

Second: 47 UMa b and c planetary system (RV-discovered gas giants)

Future gas giant reflected light spectra

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Gas giant planet albedo spectra

High contrast exoplanet imaging 2027+

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Roman CGI contrast (2027 launch): may see large or young planets in visible-light

E-ELT Planetary Camera and Spectrograph can image nearby M dwarf planets in near-infrared

(maybe 2035: second generation)

Roman (space) visible light

ELT PCS visible and near-IR

Habitable Worlds Observatory�Seeking the Story of the Universe and Life within it

Exploring the Habitable Worlds Observatory Trade Space�Three Initial Exploratory Analytic Cases�

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Off-axis 6m ID/7.2m OD

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Off-axis, 6m

First round cases fit in fairings currently in development

New Glenn (case on left) and Starship Standard Volumes (all)

On-axis, 8m (round)

EAC 1

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EAC 2

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EAC 3

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Another Earth

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Preliminary simulated high-contrast image of the

Solar System with a coronagraph on HWO

Credit: Kammerer, Pueyo (STScI), Juanola Parramon, Stark (GSFC)

Earth is more than one planet

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(now)

a

13%

39%

48%

now

Early Earth

Earth is more than one planet

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(now)

a

now

Early Earth

Earth is more than one planet

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(now)

Credit: LUVOIR & HabEx Final Reports

Arney, Domagal-Goldman, Griswold (GSFC)

now

Early Earth

Searching for global biospheres

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Credit: Lustig-Yaeger (JHU-APL),

Robinson (NAU), Arney (GSFC)

Searching for global biospheres

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Rayleigh Scattering

Searching for global biospheres

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Searching for global biospheres

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Comparative planetology

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Credit: Arney, Roberge (GSFC)

Preliminary simulations

Hundreds of other types of exoplanets found during a habitable planet survey

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Direct & transit spectroscopy both possible

Thank you

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