A recently released set of topographic maps provides new evidence for an ancient northern ocean on Mars. The maps offer the strongest case yet that the planet once experienced sea-level rise consistent with an extended warm and wet climate, rather than the harsh, frozen landscape that exists today. “One of the most important points here is that the existence of an ocean of this size means a higher potential for life,” said Benjamin Cardenas, assistant professor of geosciences at Penn State and lead author of the recently published study. in Journal of Geophysical Research: Planets. “It also tells us about the ancient climate and how it evolved. Based on these findings, we know that there must have been a time when it was warm enough and the atmosphere was thick enough to support that much liquid water at once.”
Whether Mars had an ocean in its low northern hemisphere has long been debated in the scientific community, Cardenas explained. Using topographic data, the research team was able to show definitive evidence of a roughly 3.5-billion-year-old coastline with significant sedimentary accumulation, at least 900 meters thick, covering hundreds of thousands of square kilometers.
“The big, new thing we did in this paper was to think about Mars in terms of its stratigraphy and its sedimentary record,” Cardenas said. “On Earth, we map the history of waterways by looking at sediment that is deposited over time. We call it stratigraphy, the idea that water transports sediment, and you can measure changes on Earth by understanding the way sediment accumulates . That’s what we ended up with here – but it’s Mars.”
The team used software developed by the United States Geological Survey to map data from the National Aeronautics and Space Administration (NASA) and the Mars Orbiter Laser Altimeter. They discovered over 6,500 kilometers of river ridges and grouped them into 20 systems to show that the ridges are likely eroded river deltas or submarine channel belts, remnants of an ancient Martian coastline.
Elements of the rock formations, such as ridge system thicknesses, elevations, locations, and possible sediment flow directions, helped the team understand the evolution of the paleogeography of the region. The area that was once an ocean is now known as Aeolis Dorsa and contains the densest collection of fluvial ridges on the planet, Cardenas explained. “The rocks at Aeolis Dorsa capture some fascinating information about what the ocean was like,” he said. “It was dynamic. The sea level rose significantly. Rocks were deposited rapidly along its basins. There were many changes here.”
Cardenas explained that Earth’s ancient sedimentary basins contain the stratigraphic record of evolving climate and life. If scientists want to find a record of life on Mars, the most logical place to start would be an ocean as large as the one that once covered Aeolis Dorsa. “The main goal of the Mars Curiosity rover missions is to look for signs of life,” Cardenas said. “It’s always looked for water, for signs of habitable life. This is the biggest yet. It’s a giant body of water fed by sediments coming from the highlands, probably carrying nutrients. If there were tides on ancient Mars, they were here, gently bringing in and releasing water. That’s exactly the kind of place where ancient Martian life could have developed.”
Cardenas and his colleagues mapped what they determined to be other ancient waterways on Mars. A forthcoming study in the Journal of Sedimentary Research shows that the various outcrops visited by the Curiosity rover were likely sedimentary layers from ancient river beds. Another paper published in Nature Geoscience applies an acoustic imaging technique used to image the stratigraphy beneath the Gulf of Mexico seafloor to a model of Mars-like erosion. Scientists have determined that landforms called fluvial ridges, found widely on Mars, are likely ancient fluvial deposits eroded from large Aeolis Dorsa-like basins.
“The stratigraphy we’re interpreting here is quite similar to the stratigraphy on Earth,” Cardenas said. “Yes, it sounds like a big claim to say we’ve discovered records of major waterways on Mars, but it’s actually relatively mundane stratigraphy. Once you get the hang of it, it’s textbook geology. The interesting part, of course it’s on Mars?” Another co-author of the JGR: Planets article is Michael P. Lamb, professor of geology at Caltech. The work was funded by the National Aeronautics and Space Administration (NASA).
Source Reference: Benjamin T. Cardenas, Michael P. Lamb. Paleogeographic Reconstructions of an Ocean Margin on Mars Based on Deltaic Sedimentology at Aeolis Dorsa. Journal of Geophysical Research: Planets, 2022; 127 (10) DOI: 10.1029/2022JE007390
