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

(Phys.org) —Researchers at the California Institute of Technology (Caltech) have discovered evidence for an ancient delta on Mars where a river might once have emptied into a vast ocean.

This ocean, if it existed, could have covered much of Mars's northern hemisphere—stretching over as much as a third of the planet.

"Scientists have long hypothesized that the northern lowlands of Mars are a dried-up , but no one yet has found the smoking gun," says Mike Lamb, an assistant professor of geology at Caltech and a coauthor of the paper describing the results. The paper was published online in the July 12 issue of the Journal of Geophysical Research.

Although the new findings are far from proof of the existence of an , they provide some of the strongest support yet, says Roman DiBiase, a postdoctoral scholar at Caltech and lead author of the paper.

Most of the northern hemisphere of Mars is flat and at a lower elevation than the southern hemisphere, and thus appears similar to the ocean basins found on Earth. The border between the lowlands and the highlands would have been the coastline for the hypothetical ocean.

The Caltech team used new high-resolution images from the Mars Reconnaissance Orbiter (MRO) to study a 100-square-kilometer area that sits right on this possible former coastline. Previous  have shown that this area—part of a larger region called Aeolis Dorsa, which is about 1,000 kilometers away from Gale Crater where the Curiosity rover is now roaming—is covered in ridge-like features called inverted channels.

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