New evidence for an ancient northern ocean on Mars has been uncovered in a recently released set of topography maps. These maps offer the strongest case yet that the planet once experienced sea-level rise consistent with an extended warm and wet climate, which was far different than the harsh, frozen landscape that exists today.
“What immediately comes to mind as one the most significant 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 on the study recently published in the Journal of Geophysical Research: Planets. “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.”
Whether Mars had an ocean in its low-elevation northern hemisphere has long been debated in the scientific community, Cardenas explained. Using topography data, the research team was able to show definitive evidence of a roughly 3.5-billion-year-old shoreline with substantial sedimentary accumulation, at least 900 meters (3,000 feet) thick, that covered hundreds of thousands of square kilometers.
A recently released set of topography maps provide new evidence for an ancient northern ocean on Mars. Benjamin Cardenas, assistant professor of geosciences at Penn State says the maps offer the strongest case yet that the planet once experienced sea-level rise consistent with an extended warm and wet climate, not the harsh, frozen landscape that exists today. Credit: Penn State
“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.”
In a region called Aeolis Dorsa, features resembling river deltas and underwater marine channels extend for 6,500 km along the edge of a low lying basin. The features show depots of sediment up to 900 metres deep, believed to have been created when fast-moving river water met with the slower-moving ocean, forming deltas.
This ocean would have existed 3.5 billion years ago when Mars was a much warmer and wetter world, and much more Earth-like.
That was also the time when life was emerging on our planet, so of course it’s natural to ask if it’s possible that life emerged there too?
That is one of the most fundamental unanswered questions in science.
This is not the first time evidence for water on Mars has been found. In fact, the much of the history of Mars exploration has been focused on the search for water, dating back to 1877 when Italian astronomer Giovani Schiaparelli thought he saw lines on Mars through his telescope. He called these lines canali, which is Italian for channels.
American astronomer Percival Lowell took it one step further claiming in publications in the first decade of the 20th century, that the lines were artificial canals, suggesting a civilization of Martians who were great engineers. Of course, that helped inspire many of the science fiction stories of invasions from Mars by little green men in menacing machines, most famously H.G. Wells’ enormously influential War of the Worlds.
It was not until 1971 that NASA’s Mariner 9, the first spacecraft to orbit Mars, spotted what indeed looked like river channels, although not large enough to be seen through Earthly telescopes. Since then, robots that have visited the planet have found more evidence of water that flowed in the past. The two rovers currently operating on the surface, Curiosity and Perseverance, were sent to craters that were thought to have once been lakes.
The researchers in this latest study do not estimate how long the ocean on Mars could have existed, whether it was there for millions of years or a period too short for life to take hold. What we do know is that at some point Mars transformed from a water world into a desert. The atmosphere became thin, temperatures dropped and the planet’s liquid water froze in the polar ice caps and underground permafrost.
To try to answer the question of whether life emerged while that water was liquid, NASA and the European Space Agency are planning a Mars Sample Return mission to collect dirt and rock samples that are currently being gathered by the Perseverance rover. The robotic mission is meant to land, load the samples, and return them to Earth for detailed laboratory study.
If no signs of life or fossils are found in those samples it’s not the end of the story. Perhaps we just need to dig deeper -– perhaps in the ocean basin — to find evidence of life from a time when the Red Planet was blue.