In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars. - Squyres SW; Grotzinger JP; Arvidson RE; Bell JF 3rd; Calvin W; Christensen PR; Clark BC; Crisp JA; Farrand WH; Herkenhoff KE; Johnson JR; Klingelhöfer G; et al. (Science (New York, N.Y.), 2004)