Opportunity’s hematite clues
At Meridiani Planum, Opportunity found small hematite-rich spherules. Their composition and geological setting pointed to water-related processes. The surrounding rocks also recorded conditions that were salty and acidic in some ancient environments.
Spirit’s silica-rich soil
Spirit’s investigation near Home Plate uncovered soil rich in silica. On Earth, similar silica deposits can be associated with hot springs and steam vents. The discovery pointed to ancient hydrothermal activity — an environment where hot water and rock interacted.
A broader story in the rocks
Opportunity later examined clay minerals and other deposits at Endeavour Crater that indicated water under more neutral conditions. These findings broadened the picture of ancient Mars: the planet experienced different watery environments, some more favourable to life than others.
What the evidence established
Source: NASA science highlights. Narrative is presented in first person as a storytelling device; the rovers were robotic spacecraft. Mars Exploration Rovers · NASA/JPL-Caltech.