Detection of silica-rich deposits on Mars

Mineral deposits on the martian surface can elucidate ancient environmental conditions on the planet. Opaline silica deposits ( as much as 91 weight percent SiO2) have been found in association with volcanic materials by the Mars rover Spirit. The deposits are present both as light- toned soils and as bedrock. We interpret these materials to have formed under hydrothermal conditions and therefore to be strong indicators of a former aqueous environment. This discovery is important for understanding the past habitability of Mars because hydrothermal environments on Earth support thriving microbial ecosystems.