Kavli Affiliate: Dimitri Mawet| Summary:With four giant planets ($msim5-10~M_rm Jup$, $T_rmeffsim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formation and probing compositional trends across the protoplanetary disk. We present new JWST/NIRSpec IFU observations ($2.85-5.3~μ$m, $Rapprox2700$) that now include the spectrum of HR 8799 b, and higher S/N spectra for HR 8799 c, d, and e compared to that in Ruffio & Xuan et al. 2026. We detect CO, CH$_4$, H$_2$O, H$_2$S, CO$_2$, and for planet b, NH$_3$. We combine the NIRSpec spectra with $1-5 μ$m photometry to perform atmospheric retrievals that account for disequilibrium chemistry and clouds, and allow C/H, O/H, N/H, and S/H to scale independently. While the four planets are similarly enriched in carbon and oxygen, with C/H and O/H between $3-5times$ stellar, we observe a tentative trend of increasing S/H – a tracer of refractory solids – from $2-5 times$ stellar with increasing orbital distance. From HR 8799 b’s NH$_3$ abundance, we estimate $rm N/H=21.2^+16.2_-8.8times$ stellar, suggesting the outer planet accreted significant amounts of N-rich gas. Overall, the elemental abundance patterns we observe are consistent with a picture where planet b formed between the CO snowline and the more-distant N$_2$ snowline, while the inner planets accreted $3 times$ stellar CO-enriched disk gas within the CO snowline. The excess volatile mass from pebble drift and evaporation implies an integrated pebble flux of $750 pm 200~M_oplus$. The increase in the planets’ S/H with orbital distance implies more solid accretion further out, which is quantitatively compatible with expectations from both pebble and planetesimal accretion ($2 times$ Minimum Mass Solar Nebula) paradigms.| Search Query:arXiv Query: search_query=au:”mawet dimitri”&id_list=&start=0&max_results=10Read More