Comparison of exhumed delta in sedimentary rocks on Mars (left) with a modern delta on Earth (right). On the left, a shaded relief map shows elevated, branching, lobate features in Aeolis Dorsa, Mars, interpreted as resistant channel deposits that make up an ancient delta. These layered, cross-cutting features are typical of channelized sedimentary deposits on Earth and here are indicative of a coastal delta environment. Credit: DiBiase et al./Journal of Geophysical Research/2013 and USGS/NASA Landsat

Scientists studying data from NASA's Mars Reconnaissance Orbiter (MRO) have discovered new evidence that Mars may have once had a vast ocean on its surface. The research team spotted an ancient delta where a river might have emptied into an ocean so large that it covered much of the planet's northern hemisphere.
Delta-like features have been found on Mars before, but most of them appear to flow into craters or similar geological boundaries, and not into places where ocean-sized bodies of water would have been likely to exist. The newly identified delta was found on what would have been the coastline of Mars' ancient ocean, and geological evidence in the delta points toward the ocean's existence.
Mars' northern lowlands have previously been compared to ocean basins on Earth, and scientists have long suspected that this flat area of low elevation is the remnant of an ancient martian seabed. The recent study provides new support for that theory.
The study could also help astrobiologists understand past environments on Mars where surface water persisted for long periods of time. This is important in determining whether or not habitats on ancient Mars were capable of supporting life as we know it.
The study, "Deltaic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars," was published in the July 12 issue of the Journal of Geophysical Research .
Source: [CalTech]