Direct Imaging Characterisation of Exoplanets: Studying Storms and Searching for Saturns

With the advent of JWST and the launch of Roman in 2027, the next 5 years represent a step-change in our ability to characterize the atmospheres of known directly imaged exoplanets and to directly image lower-mass and cooler exoplanets. We propose a transformational program that will lead from the characterization of currently known directly imaged exoplanets and brown dwarfs to the first direct images of young Saturn mass and solar-system age giant planets. Characterizing the atmospheres of these planets is a key science goal and perfecting the technology and techniques to do so will be critical for the success of future space missions such as the Habitable Worlds Observatory, which will yield the first images of potentially habitable true Earth twins.  We propose 3 work packages using VLT, JWST, and Roman:
1) A 3-d view of brown dwarf and giant exoplanet atmospheres: Variability monitoring probes the 3-d time-resolved structure of exoplanet atmospheres. In Cycle 2, JWST will measure spectroscopic variability for 5 L/T transition brown dwarfs and young planetary mass objects (GO 2965, 3548, 3375, 3181, PIs Biller, Vos, Whiteford, Zhou). Coverage of spectral features inaccessible from the ground will lend direct insight into the structure of these atmospheres and the mechanism driving variability.  We will also extend variability monitoring to high-contrast companions using the novel VLT/ERIS vAPP coronagraph (2 nights of monitoring acquired in October 2023, PI Sutlieff).
2) Completing the census of young Jupiters: we are conducting a VLT/ERIS + SPHERE survey for young giant planets in overlooked nearby young associations to improve the census of giant planets at the youngest ages (<10 Myr) and determine how companion fraction varies as a function of association age.
3) The First Direct Images of young sub-Jupiter planets and Solar System Age Giant Planets: Several JWST/NIRCam surveys are underway to image down to Saturn mass companions for nearby young stars (GO 4050, PI Carter, co-I Biller, Survey 6005, PI Biller, GO 5835, PI Carter, co-I Biller).  Our team is playing a leading role in these surveys.  In 2026, Gaia DR4 will provide a treasure trove of ~10000 astrometrically detected planets. Roman may image the brightest of these planets, yielding the first direct images of solar system age giant planets. PI Biller is an ESA-appointed representative to the Roman Coronagraph Community Participation Program. Combining JWST, Gaia, and Roman results will enable the most in-depth study of giant exoplanet demographics to date.