Mars may once have been flooded with water, according to a Nasa study looking into mud minerals across the planet.
These colourful photos (above) show different types of clay minerals which result from wet conditions.
Although the water was only around for short bursts, the study suggests that Mars had a warm, wet environment.
"If surface habitats were short-term, that doesn't mean we should be glum about prospects for life on Mars, but it says something about what type of environment we might want to look in," said the report's lead author, Bethany Ehlmann, assistant professor at the California Institute of Technology and scientist at NASA's Jet Propulsion Laboratory in Pasadena.
"The most stable Mars habitats over long durations appear to have been in the subsurface. On earth, underground geothermal environments have active ecosystems."
The study suggests that warm water may have mainly sat below the surface, while brief bursts of surface water caused the erosion we see in photos like the one (below), taken in April this year.
Mars' thin atmosphere means water could not stay around for long before evaporating or freezing, so scientists are looking into what may have caused it to thin over time.Suggest a correction