Hello, I’m Will Balmer.

With fellow co-PI Daniella Bardalez Gagliuffi, I planned and took the first coronagraphic images of the nearby exoplanet 14 Herculis c, one of the coldest and oldest gas giants imaged to date. The planet orbits on a wide, elliptical path that is misaligned with the inner planet in the system, 14 Herculis b. This is a wildly different architecture compared to our own solar system, where all the (large) planets orbit in the same orbital plane, and are aligned with the Sun’s rotation axis. This indicates that the two planets in the 14 Herculis system underwent a gravitational tug of war at some point in their history, and that the outer planet was kicked onto its present orbit in a process called “planet-planet scattering.” The planet is a lot fainter in the 4.4 micron filter than we expected, based on how massive and old it is, so we believe that strong updrafts are cycling opaque gases from the planet’s warm interior into its upper atmosphere, where some of its outbound light is blocked from our view. You can read our press release here. The paper was published in the Astrophysical Journal Letters, and you can find a pre-print of the article here.

In particular, our JWST observations show clear carbon dioxide absorption (CO₂) in the spectrum of each planet in the HR 8799 system, which, compared to the clear carbon monoxide absorption (CO), gives us a handle on the relative enrichment of heavy elements in these planet’s atmospheres. We also observed the young, Jupiter-mass planet 51 Eri b. Despite how faint this planet is, we were able to detect it at a wavelength of 4.1 microns, which tells us indirectly about how hot the planet is, and how much CO₂ is in its atmosphere. These measurements place constraints on the accretion history of these planets, in particular, indicating an early accretion of solids. We hope to apply these techniques to characterize more systems in the near future. I was awarded about 23 hours of additional JWST observing time to repeat this experiment in four additional directly imaged systems. That means four more beautiful images of giant exoplanets from JWST coming soon!

I recently co-led a JWST Cycle 2 Director’s Discretionary program with Kyle Franson to characterize the atmosphere and thermal budget of AF Lep b with JWST/NIRCam imaging. With a separation from its bright host star of only 0.3 arcseconds (about 2λ/D, and 7% coronagraphic throughput) at the time of observation, the planet was particularly challenging to recover with JWST. Nevertheless, in observations I planned based on a feasibility study I led, we successfully recovered the planet at a high significance at its expected location. I am second author on an excellent paper by Kyle describing the exciting evidence for disequilibrium chemistry and enhanced metallicity, which we were able to learn by detecting the planet in these wavelengths.