James Webb Space Telescope Feed Post

Arxiv: BOWIE-ALIGN: JWST reveals hints of planetesimal accretion and complex sulphur chemistry in the atmosphere of the misaligned hot Jupiter WASP-15b Published: 10/10/2024 8:01:53 PM Updated: 10/10/2024 8:01:53 PM

Paper abstract: We present a transmission spectrum of the misaligned hot Jupiter WASP-15bfrom 2.8--5.2 microns observed with JWST's NIRSpec/G395H grating. Our highsignal to noise data, which has negligible red noise, reveals significantabsorption by H_2O (4.2\sigma) and CO_2 (8.9\sigma). From independentdata reduction and atmospheric retrieval approaches, we infer that WASP-15b'satmospheric metallicity is super-solar (\gtrsim 15\times solar) and its C/Ois consistent with solar, that together imply planetesimal accretion. Our GCMsimulations for WASP-15b suggest that the C/O we measure at the limb is likelyrepresentative of the entire photosphere due to the mostly uniform spatialdistribution of H_2O, CO_2 and CO. We additionally see evidence forabsorption by SO_2 and absorption at 4.9\mum, for which the current leadingcandidate is OCS, albeit with several caveats. If confirmed, this would be thefirst detection of OCS in an exoplanet atmosphere and point towards complexphotochemistry of sulphur-bearing species in the upper atmosphere. These arethe first observations from the BOWIE-ALIGN survey which is using JWST'sNIRSpec/G395H instrument to compare the atmospheric compositions ofaligned/low-obliquity and misaligned/high-obliquity hot Jupiters around F starsabove the Kraft break. The goal of our survey is to determine whether theatmospheric composition differs across two populations of planets that havelikely undergone different migration histories (disc versus disc-free) asevidenced by their obliquities (aligned versus misaligned).