BERLIN (AP) — Scientists say images of Martian craters taken by European and American space probes show there likely once was a planet-wide system of underground lakes.

Researches in Italy and the Netherlands say data collected by NASA and ESA probes orbiting the red planet provide the first geological evidence for a large groundwater system on Mars.

Francesco Salese, one of the scientists involved, said in an email Friday that the findings confirm earlier models and smaller-scale studies, and that the lakes may have been connected to each other.

Ralf Jaumann, a planetary scientist at the German Aerospace Center who wasn't directly involved in the study, said future Mars landers will be examining the craters for signs of ancient life.

He said large amounts of frozen water may still exist below the surface.