Curiosity Views Rocks With 'Halos'

While exploring Gediz Vallis channel, NASA's Curiosity Mars rover came across rocks that show a pale color near their edges. These rings of color changes, also called halos, resemble markings seen on Earth when groundwater leaks into rocks along fractures, causing chemical reactions that change the color. The markings were revealed over eons, after wind and sand eroded the debris pile.