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Three billion years ago, the red, dusty planet we now consider was a very different world and could have supported life. Recently, American scientists have uncovered hard and strong evidence for the presence of an ancient ocean on Mars, ending the debate about the oceanic past of parts of this now cold and frozen planet. These discoveries will certainly shed light on the possible origin of life on Mars.
In 2013, almost 10 years ago, scientists at the California Institute of Technology (Caltech) discovered evidence of an ancient delta on Mars where a river may have flowed into a vast ocean. For the study’s authors, this ocean, if it existed, could cover much of the northern hemisphere of Mars, stretching across nearly a third of the planet.
Satellite images showed that one area, part of a larger area called Aeolis Dorsa (the current study area), showed back channel or river ridge structures. These are formed when coarse materials such as large gravel and pebbles are transported along rivers and deposited on bottoms that accumulate over time. Their topographic arrangement was consistent with the hypothesis of a river delta flowing into the ocean. Although these discoveries were far from proving the existence of an ancient ocean itself, they provided one of the strongest supports to date.
Then more evidence began to accumulate confirming the ancient presence of water, without ever providing formal proof of the presence of an ocean, other than by modeling.
Researchers from Penn State University recently published in the journal Journal of Geophysical Research: Planets, a set of topographic maps providing 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 hot and humid climate, rather than the harsh, frozen landscape that exists today.
An unequivocal answer to a long-standing scientific debate
Whether Mars has a low-altitude ocean in its northern hemisphere has long been debated in the scientific community, says Benjamin Cardenas, assistant professor of geosciences at Penn State and lead author of the study. In 2015, NASA reconfirmed the hypothesis of an early Martian ocean containing more water than Earth’s Arctic Ocean, based on ground-based observatories and measurements of water signatures in the Martian atmosphere.
About 4.3 billion years ago, Mars would have had enough water to cover its entire surface with a layer of liquid about 137 meters deep. More likely, the water would have formed an ocean covering nearly half of the northern hemisphere, reaching depths greater than 1 mile in some areas.
In the current study, using topographic data, the research team was able to demonstrate definitive evidence of an approximately 3.5-billion-year-old shoreline with significant sedimentary accumulation, at least 900 meters thick, covering hundreds of thousands of square kilometers.
Specifically, the team used software developed by the United States Geological Survey to map data from NASA and the Mars Orbiter laser altimeter. They discovered more than 6,500 kilometers of river ridges, like those just revealed in 2015 by NASA, and grouped them into 20 systems to show that the ridges are likely eroded river deltas or channel belts beneath marinas, remnants of an ancient Martian coastline.
Use the stratigraphy of Earth, but on Mars
Benjamin Cardenas declares va communicated : “ The big news we have in this paper was to think about Mars in terms of stratigraphy and the sedimentary record. On Earth, we trace the history of waterways by examining the sediments that are deposited over time. We call it stratigraphy, the idea that water carries sediment, and you can measure changes on Earth by understanding how that sediment accumulates. That’s what we did here, but with Mars “.
Elements of the rock formations, such as ridge system thicknesses, elevations, locations, and possible directions of sediment flows, 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, as mentioned earlier, and contains the densest collection of river ridges on the planet.
In addition, Cardenas and his colleagues mapped what they determined to be other ancient waterways on Mars. The upcoming study in Journal of Sedimentary Research shows that the various outcrops visited by the Curiosity rover were probably sedimentary layers of ancient river banks.
Not to mention that another article published in Nature Geoscience applies an acoustic imaging technique used to visualize the stratigraphy beneath the seafloor of the Gulf of Mexico to a model of Mars-like erosion. Researchers confirm that fluvial ridges on Mars are likely ancient fluvial deposits eroded from large Aeolis Dorsa-like basins.
The Search for Martian Life
The researcher points out that the rocks in this area, like any sedimentary rock on Earth, capture information about the state of the ocean, the evolution of climate and life. He adds: “ It was dynamic. The sea level has risen significantly. Rocks were quickly being deposited along his pans. There have been many changes here “.
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. Indeed, the geography estimated by the authors of the study supports the idea that the area would have been fed by sediments originating from the highlands, likely carrying nutrients.
Benjamin Cardenas explains: If there were tides on ancient Mars, they would be here, gently bringing in and leaving water. This is exactly the type of place where ancient Martian life could have developed “.