A global Mars dust composition refined by the Alpha‐Particle X‐ray Spectrometer in Gale Crater

Abstract Modern Martian dust is similar in composition to the global soil unit and bulk basaltic Mars crust, but it is enriched in S and Cl. The Alpha Particle X‐ray Spectrometer (APXS) on the Mars Science Laboratory Curiosity rover analyzed air fall dust on the science observation tray (o‐tray) in Gale Crater to determine dust oxide compositions. The o‐tray dust has the highest concentrations of SO 3 and Cl measured in Mars dust (SO 3 8.3%; Cl 1.1 wt %). The molar S/Cl in the dust (3.35 ± 0.34) is consistent with previous studies of Martian dust and soils (S/Cl = 3.7 ± 0.7). Fe is also elevated ~25% over average Mars soils and the bulk crust. These enrichments link air fall dust with the S‐, Cl‐, and Fe‐rich X‐ray amorphous component of Gale Crater soil. Dust and soil have the same S/Cl, constraining the surface concentrations of S and Cl on a global scale.