What evidence indicates that liquid water existed existed on Mars in the past?

Evidence indicating that liquid water existed on Mars in the past includes the presence of ancient river valleys, lakebeds, and mineral deposits such as clays and sulfates that typically form in aqueous environments. Orbital imagery has revealed features resembling deltas and outflow channels, suggesting extensive flooding. Additionally, rovers have detected specific minerals that only form in the presence of water, supporting the idea that Mars had a wetter climate in its history.