James Webb Space Telescope Exoplanet Imaging

I am Co-PI of one of thirteen Early Release Science programs selected to obtain the first science images with JWST.  Our team observed 3 planetary systems to demonstrate JWST’s high-contrast imaging capabilities, and also obtain the first images and spectra of exoplanets covering an extraordinary 1-20 μm bandpass.  An overview of the project is published here.  Exoplanet high-contrast images are published here.  A 1-20 µm spectrum of a planetary-mass companion is published here.

JWST coronagraphic images of the exoplanet HIP 65426b from Carter et al. (2022).

JWST spectra of the planetary mass companion VHS 1256b from Miles et al. (2022).  Top panel: Full JWST spectrum of VHS 1256 b.  Bottom panel: Zoom-in on the 4.7 micron CO bandhead.

Characterizing Exoplanet Atmospheres with Multi-Wavelength Imaging

By imaging exoplanets at multiple wavelengths, it is possible to characterize their bulk properties and atmospheric parameters.  My group has worked to expand the wavelength range over which we characterize extrasolar planets, in particular, pushing into the thermal infrared (>3 μm), where self-luminous, gas-giant exoplanets peak in brightness.  Our work has demonstrated the ubiquity of clouds and non-equilibrium chemistry on directly imaged planets , as well as the first evidence for metal enhancement in a directly-imaged planet.  We’ve also been working with the KPIC team to obtain exoplanet spins and radial velocities via high-dispersion coronagraphy.

Some directly imaged planets from LBTI/LMIRcam

Spectroscopy of the Cold Exoplanet Analogs

The difficulty of studying planets around other stars is that the planets are much fainter than their host stars.  Dedicated instruments, such as the Gemini Planet Imager, can detect the light of warm Jupiter-mass analogs.  However, the capability does not yet exist to image a planet as cold as Jupiter around another star.

While we develop more sensitive instrumentation, we can learn about cold exoplanet atmospheres by studying their isolated analogs, brown dwarfs.  My group used the Gemini telescope on Mauna Kea to obtain the first spectrum of the coldest brown dwarf, WISE 0855, which at 250 K, is colder than the telescope I used to observe it!  Our spectrum shows muted absorption features that are consistent with a cloudy atmosphere, which at these temperatures, are probably made of water or water ice.  Further work with Gemini shows the ubiquity of non-equilibrium CO chemistry and evidence for a detached radiative zone.  We also received Cycle 1 JWST time to study WISE 0855 in detail, and search for variability from water ice clouds.

Gemini/GNIRS spectrum of WISE 0855, a 250 K brown dwarf that is the first object outside of the Solar System to show evidence for water clouds.