why is mars red

Mars is red primarily because of a water-rich iron mineral called ferrihydrite found in the dust covering its surface. This mineral contains iron oxide, which formed when iron in Martian rocks interacted with water and possibly oxygen billions of years ago, creating the rusty reddish color seen today. This finding revises the older theory that Mars' red color was due mainly to hematite, a dry, rust-like mineral. The presence of ferrihydrite suggests Mars had a wetter and potentially more habitable environment in its ancient past before becoming the cold, dry planet it is now.