Abstract:
Unraveling the formation and origin of giant planets is a complex
problem which requires the use of multiple independent formation
tracers. Measuring the chemical abundances in giant planet atmospheres
is one powerful approach because the formation environment, timescale,
and processes are expected to leave an imprint on the planets’
atmospheric composition. Dynamical mass measurements together with
predictions from evolutionary models of young giant planets are another
pathway to constrain their formation history because different formation
mechanisms predict different initial entropies and cooling tracks for
the planets. In the past three years, the GRAVITY interferometer has
directly detected additional inner giant planets in the beta Pic and HD
206893 systems, heralding a new era of planet formation studies by
directly testing evolutionary models through combining luminosities from
direct imaging with dynamical masses from radial velocities or Gaia
accelerations. Measurements of the C/O abundance ratio from the GRAVTY
K-band spectra provide complementary constraints on the planets’
formation and evolution history by studying the enrichment of heavy
elements in the planets’ atmospheres.
The suite of high-contrast imaging modes on JWST can be used to increase
the spectral coverage and improve the constraints on atmospheric
abundances and bolometric luminosity of these substellar companions. On
the one hand, JWST aperture masking interferometry (AMI) provides unique
access to giant planet and brown dwarf atmospheres at high angular
resolution in the 3-5 µm domain. The JWST AMI bands are sensitive to CO,
CH4, and H2O absorption and together with the GRAVITY spectrum they
constrain the non-equilibrium chemistry in these objects’ atmospheres.
On the other hand, JWST coronagraphy yields unparalleled sensitivity
down to Saturn-mass companions, albeit at larger angular separations
than AMI. The combination of GRAVITY with JWST opens up the direct
characterization of close-in giant exoplanets on Solar System-like
scales which are predicted to be common from radial velocities or Gaia
accelerations, enabling the study of both atmospheric and evolutionary
formation tracers to reveal their origin.