Discovery of alunite in Cross crater, Terra Sirenum, Mars: Evidence for acidic, sulfurous waters

Murchie, Scott L.; Ehlmann, Bethany L.; Mustard, John F.; Clark, Roger N.; Gondet, Brigitte; Milliken, Ralph E.; Wray, James J.; Calvin, Wendy M.; Seelos, Kimberly D.; Poulet, Francois; Carter, John; Swayze, Gregg A.; Breit, George N.; Benzel, William M.