Ancient traces of a vast ocean have just been discovered on Mars

You’re no doubt familiar with the dry, dusty appearance of Mars as it appears today — but scientists have found evidence of a vast ocean that existed on the red planet’s surface some 3.5 billion years ago, likely covering hundreds of thousands of square kilometers .

This evidence comes in the form of distinctive coastal topography identified through numerous satellite images of the Martian surface. If these images are taken at slightly different angles, a relief map can be created.

Researchers have been able to map more than 6,500 kilometers (4,039 miles) of river ridges that appear to have been carved by rivers, showing they are most likely eroded river deltas or submarine channel belts (channels carved into the sea floor).

“The big, novel thing we did in this work was think about Mars in terms of its stratigraphy and its sedimentary record,” says Pennsylvania State University geoscientist Benjamin Cardenas.

“On Earth, we record the history of waterways by looking at sediments deposited over time. We call this stratigraphy, the idea that water transports sediment, and you can measure changes on Earth by understanding how sediment accumulates. That’s what we did here – but it’s Mars.”

Using Mars Reconnaissance Orbiter data collected in 2007, the team performed an analysis of ridge thickness, angles and positions to understand the study area: the topographical depression on Mars known as the Aeolis Dorsa region.

It seems likely that a significant change occurred in this part of the planet all those years ago, Cardenas explains. This is shown by the evidence of significant sea level rise and the rapid movement of rocks by rivers and currents. Today, Aeolis Dorsa contains the most concentrated collection of river ridges on Mars.

All of this is related to the search for life on Mars. One of the most fundamental questions scientists grapple with regarding the Red Planet is whether conditions hospitable enough to support life have ever existed.

“What immediately comes to mind as one of the most important points is that the existence of an ocean this size means a higher potential for life,” says Cardenas.

“It also tells us something about the ancient climate and how it evolved. Based on these findings, we know there must have been a time when it was warm enough and the atmosphere was thick enough to hold that much liquid water at once.”

Researchers don’t stop at the Aeolis Dorsa region.

In a separate study published in nature geosciencesSome of the same researchers, including Cardenas, applied an acoustic imaging technique used to map ancient sea floors in the Gulf of Mexico to create a model showing how water might have eroded the surface of Mars.

There are huge areas of what could be river ridges all over Mars, and the simulations the team have run remarkably resemble the shape of the red planet’s landscape – suggesting there was extensive water cover at one time.

We’re seeing increasing evidence that water was once abundant on Mars, and work continues to find out what it might have led to and where that water is now — though looking back billions of years isn’t easy .

“If there were tides on ancient Mars, they would have been here, gently bringing water in and out,” says Cardenas. “This is exactly the kind of place where ancient Martian life might have evolved.”

The research was published in Journal of Geophysical Research: Planets and nature geosciences.