Scientists have found evidence of an ancient ocean on Mars which they say increases the "potential for life".
Topography maps were closely analysed by researchers, who found traces of a northern hemisphere ocean that experienced sea level rises consistent with a warm and wet climate.
Experts have long debated the possibility of life on Mars and whether it had been home to oceans.
The data is based on "recently released" topography and the findings assume that "erosion has not significantly reshaped the Martian surface over the last 3.5 billion years".
Researchers were able to show "definitive evidence" of a shoreline with "substantial sedimentary accumulation" which was at least 900m thick covering thousands of square miles.
Benjamin Cardenas, an assistant professor in the geosciences department at Pennsylvania State University and the study's lead author, said: "What immediately comes to mind as one of the most significant points here is that the existence of an ocean of this size means a higher potential for life.
"It also tells us about the ancient climate and its evolution.
"Based on these findings, we know there had to have been a period when it was warm enough and the atmosphere was thick enough to support this much liquid water at one time.
"On Earth, we chart the history of waterways by looking at sediment that is deposited over time.
"We call that stratigraphy, the idea that water transports sediment and you can measure the changes on Earth by understanding the way that sediment piles up.
"That's what we've done here - but it's Mars."
He said the area that was home to the ocean is now known by scientists as Aeolis Dorsa.
Software developed by the US Geological Survey was used to map data from NASA and the Mars Orbiter Laser Altimeter, which was an instrument on a surveyor spacecraft which operated in the red planet's orbit.
The study was published in the Journal of Geophysical Research: Planets.
The findings come a month after British scientists revealed they had found evidence which gave the "best indication yet that there is liquid water on Mars".