Scientists will now attempt to learn if Mars had any standing bodies of waterlakes or even seasor if the water simply bubbled up from underground. They will also try to find out when the water disappeared.
"Understanding liquid water's role on the Martian surface in the past is key to understanding whether Mars could have been an abode for life," said Bruce Betts, director of projects at the Planetary Society in Pasadena, California.
Mars is the planet in our solar system that most closely resembles Earth. It has a rocky surface, making it easier for life to gain a foothold. Some scientists believe primitive life could survive around hydrothermal vents near the planet's surface. Today it's perhaps too cold for life to exist there, but organisms may have thrived in the past.
"Liquid water isn't stable on the surface of Mars now, but existed on the Martian surface in the past," said Betts. "More water for longer periods in the Martian past would mean more chance, presumably, for life to evolve and exist."
Mars may have been not only wetter in the past, but could have had a denser atmosphere. There is the possibility that life arose on Mars, only to die out as conditions on the planet worsened. Some researchers have suggested that future searches for life be shifted to focus on extinct, rather than extant, life.
On Earth, such extinct life can be found in the form of fossils dating from 3.5 billion years ago. But the rovers cannot date Martian rocks or detect mineral signatures left by living organisms.
While the new discovery proves that water once existed on Mars, the rovers cannot test the possibility that liquid water may still exist beneath the planet's surface.
Instead, the findings have prompted new questions of what happened to the water and atmosphere on Mars.
Scientists now hope the success of the latest mission will expand the Mars exploration program so that some of those questions can be answered. The rover missions have raised the possibility of sending a manned mission to Mars.
"Mars exploration rarely disappoints," said Betts. "It certainly didn't this time."