The latest pictures beamed back from Mars suggest Nasa's Rover Spirit may have landed on the red planet in mud.
Scientists were shocked to see the marks made by the lander's airbags scraping across the surface.
They expected the ground to crack or break but instead it rumpled up and folded, as if it was wet.
This means there might be liquid water on - or just below - Mars' surface, which could mean that at one time lakes and oceans existed there.
And if water is found in the soil on Mars then the chances of finding life on there is massively increased.
Very salty water
Scientists think that if water does exist there it would have to be very salty to stop it from freezing or evaporating.