When Opportunity landed inside a small Martian crater on the plain, known as the Meridiani Planum, its instruments detected abundant evidence of an iron oxide mineral called gray hematite-- a chemical that is almost always formed from iron in standing water.
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It launched Opportunity toward Meridiani Planum, a flat, smooth region relatively free of the reddish dust that cloaks Gusev . Scientists believe Meridiani abounds in a mineral called gray hematite, which typically forms in marine or volcanic environments rich in water.
