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So happy and proud of what William Balmer (PhD student at The Johns Hopkins University and in our group at the Space Telescope Science Institute) has managed to do with the JWST/NIRCam Coronagraphy mode. To achieve this incredible image, we had to push performance to the max, using the long wavelength bar (or wedge) occulter at its narrowest end to be able to recover planet e (the closest one) and also be able to get those new colors, only available from space.
Kellen Lawson (Postdoc NASA Goddard Space Flight Center) has managed to deconvolve coronagraphic images with a spatially varying (and complex) point spread function (PSF, the optical "response" of the telescope+instrument), an ill-posed problem but that's how we can see all 4 exoplanets simultaneously in this imaged. This is a young, scaled up version of our solar system, one of the bonafide exoplanetary systems in our field of high contrast imaging and spectroscopy. The outreach team at STScI has done a wonderful job too! https://hub.jhu.edu/2025/03/17/webb-telescope-carbon-dioxide-exoplanet/ JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO$_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres Score: 25 = category weight 1 × (3×title count 6 + abstract count 7) William O. Balmer, Jens Kammerer, Laurent Pueyo, Marshall D. Perrin, Julien H. Girard, Jarron M. Leisenring, Kellen Lawson, Henry Dennen, Roeland P. van der Marel, Charles A. Beichman, Geoffrey Bryden, Jorge Llop-Sayson, Jeff A. Valenti, Joshua D. Lothringer, Nikole K. Lewis, Mathilde M\^alin, Isabel Rebollido, Emily Rickman, Kielan K. W. Hoch, Rémi Soummer, Mark Clampin, C. Matt Mountain https://arxiv.org/abs/2503.13608 High-contrast observations with JWST can reveal key composition and vertical mixing dependent absorption features in the spectra of directly imaged planets across the 3-5 $\mu$m wavelength range. We present novel coronagraphic images of the HR 8799 and 51 Eri planetary systems using the NIRCam Long Wavelength Bar in an offset "narrow" position. These observations have revealed the four known gas giant planets encircling HR 8799, even at spatial separations challenging for a 6.5 m telescope in the mid-infrared, including the first ever detection of HR 8799 e at 4.6 $\mu$m. The chosen filters constrain the strength of CO, CH4, and CO2 absorption in each planet's photosphere. The planets display a diversity of 3-5 $\mu$m colors that could be due to differences in composition and ultimately be used to trace their formation history. They also show stronger CO2 absorption than expected from solar metallicity models, indicating that they are metal enriched. We detected 51 Eri b at 4.1 $\mu$m and not at longer wavelengths, which, given the planet's temperature, is indicative of out-of-equilibrium carbon chemistry and an enhanced metallicity. Updated orbits fit to the new measurement of 51 Eri b validate previous studies that find a preference for high eccentricities ($e{=}0.57_{-0.09}^{+0.03}$), which likely indicates some dynamical processing in the system's past. These results present an exciting opportunity to model the atmospheres and formation histories of these planets in more detail in the near future, and are complementary to future higher-resolution, continuum-subtracted JWST spectroscopy. |
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