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The Smith Cloud is a gaseous high-velocity cloud (HVC) in an advanced stateof accretion, only 2.9 kpc below the Galactic plane and due to impact the diskin 27 Myr. It is unique among HVCs in having a known distance (12.4+/-1.3 kpc)and a well-constrained 3D velocity (296 km/s), but its origin has long remaineda mystery. Here we present the first absorption-line measurements of itsmetallicity, using HST/COS UV spectra of three AGN lying behind the Cloudtogether with Green Bank Telescope 21 cm spectra of the same directions. UsingVoigt-profile fitting of the S II 1250, 1253, 1259 triplet together withionization corrections derived from photoionization modeling, we derive thesulfur abundance in each direction; a weighted average of the threemeasurements gives [S/H]=-0.28+/-0.14, or 0.53+0.21-0.15 solar metallicity. Thefinding that the Smith Cloud is metal-enriched lends support to scenarios whereit represents recycled Galactic material rather than the remnant of a dwarfgalaxy or accreting intergalactic gas. The metallicity and trajectory of theCloud are both indicative of an origin in the outer disk. However, its largemass and prograde kinematics remain to be fully explained. If the cloud hasaccreted cooling gas from the corona during its fountain trajectory, aspredicted in recent theoretical work, its current mass would be higher than itslaunch mass, alleviating the mass concern.

On the Metallicity and Origin of the Smith High-Velocity Cloud