Newly discovered traces of ocean on Mars indicate the planet may have once been hospitable

“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.”

The scientific community has long speculated that Mars may have had an ocean in its low-elevation northern hemisphere. This new topographical data showed clear evidence of a roughly 3.5-billion-year-old shoreline.

“The big, novel thing that we did in this paper was think about Mars in terms of its stratigraphy and its sedimentary record,” Cardenas said.

“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.”

To substantiate their findings, the team used software developed by the United States Geological Survey to map data from NASA and the Mars Orbiter Laser Altimeter. As such, the researchers were able to pinpoint the area that was once ocean.

This is now known as Aeolis Dorsa.

A dynamic ocean

“The rocks in Aeolis Dorsa capture some fascinating information about what the ocean was like,” he said. “It was dynamic. The sea level rose significantly. Rocks were being deposited along its basins at a fast rate. There was a lot of change happening here.”

Now Cardenas believes the area could also contain evidence of life on Mars.

“A major goal for the Mars Curiosity rover missions is to look for signs of life,” Cardenas said. “It’s always been looking for water, for traces of habitable life. This is the biggest one yet. It’s a giant body of water, fed by sediments coming from the highlands, presumably carrying nutrients. If there were tides on ancient Mars, they would have been here, gently bringing in and out water. This is exactly the type of place where ancient Martian life could have evolved.”

Cardenas and his colleagues have also mapped other ancient waterways on Mars.

“The stratigraphy that we're interpreting here is quite similar to stratigraphy on Earth,” Cardenas said. “Yes, it sounds like a big claim to say we’ve discovered records of large waterways on Mars, but in reality, this is relatively mundane stratigraphy. It’s textbook geology once you recognize it for what it is. The interesting part, of course, is it’s on Mars.”

The study was first published in the Journal of Geophysical Research: Planets on October 12.

Study abstract:

The evidence for an ancient ocean in Mars' northern hemispheric basin during the Noachian/Hesperian is contentious. Much of the work is based on the modern topography by assuming that erosion has not significantly reshaped the Martian surface over the last 3.5 billion years, despite evidence to the contrary. Here, we provide new evidence for a northern ocean or large sea based on stratigraphic analysis of sedimentary basin fill exposed at Aeolis Dorsa. We mapped over 6,500 km of fluvial ridges, grouped them into 20 systems, and present evidence that they are the eroded remnants of river deltas or submarine-channel belts, together defining the stratigraphy of an ancient ocean margin. We used Context Camera stereo-pair elevation models to measure the stratigraphic positions of each system and used branching directions to determine paleoflow directions. By grouping landforms based on stratigraphic position and paleoflow directions, we reconstructed the paleogeography at Aeolis Dorsa over 5 timesteps; all cases differ from the modern topography. We tracked the initial regression and later transgression of a shoreline during at least 900 m of sea-level rise, a scale consistent with a northern ocean on a warm and wet early Mars.