The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas

Jerry W. Xuan, Jean-Baptiste Ruffio, Yayaati Chachan +24

With four giant planets ($m\sim 5-10M_{\mathrm{Jup}}$, $T_\rm{eff}\sim900-1200$ K) orbiting between 15-70 au, HR 8799 provides an unparalleled testbed for studying giant planet formatio…