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Mars northern ocean
This artist’s impression shows Mars as it might have looked 4 billion years ago, with the complex shoreline of Chryse Planitia front and center. (Credit: M. Kornmesser / ESO)

Liquid water is almost non-existent on modern Mars, but scientists say sedimentary deposits show signs that tsunami waves as high as 400 feet washed over Martian shorelines billions of years ago.

The claim, laid out on Thursday in Nature Scientific Reports, may sound like the Red Planet equivalent of “The Day After Tomorrow,” the 2004 climate-scare movie that showed New York getting drowned. There is a climate angle to the newly published research, but a more apt comparison would be 1998’s “Deep Impact,” in which a crashing comet did something similar.

“The tsunamis could have been triggered by bolide impacts, which, about every 3 million years, generated marine impact craters approximately 30 kilometers in diameter,” study co-author Thomas Platz, a research scientist at the Planetary Science Institute in Arizona, said in a news release about the study.

As spectacular as it sounds, the findings are consistent with how mega-tsunamis happen on Earth, and what scientists expected on Mars as well. There’s lots of other geological evidence that Mars once harbored a large northern ocean. But if that’s the case, there should have been occasional asteroid or cosmic strikes that produced giant waves.

“For more than a quarter-century, failure to identify shoreline features consistently distributed along a constant elevation has been regarded as inconsistent with the hypothesis that a vast ocean existed on Mars approximately 3.4 billion years ago,” said PSI senior scientist J. Alexis Palmero Rodriguez, the study’s principal author.

A close study of imagery and elevation data from three NASA orbiters – Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter – finally turned up evidence of shoreline shifts in two regions. known as Chryse Planitia and Arabia Terra. The sedimentary deposits there point to two events that pushed debris as far as 150 miles inland.

Rodriguez said there were signs that Mars’ climate had changed between one event and the other. “During the time period that separated the two tsunami events, the ocean level receded to form a lower shoreline and the climate became significantly colder,” he said. “Evidence for climate change is reflected in the morphology of the tsunami deposits.”

The earlier event pushed boulders across the shore, and created backwash channels as waves retreated back into the ocean. But the later event pushed ice-rich lobes of sediment, which points to a dramatic chill-down. The patterns of deposits also indicate that the Martian ocean had shrunk over the course of millions of years.

Rodriguez said that may explain why the signs of shoreline features have been so hard to come by. Shifts in the shorelines may well have obscured the geological evidence.

Mars shorelines and tsunamis
Left: Color-coded digital elevation model of the study area showing the two proposed shoreline levels of an early Mars ocean that existed approximately 3.4 billion years ago. Right: Areas covered by the documented tsunami events extending from these shorelines. Click on the image for a larger version. (Credit: Alexis Rodriguez / PSI)

If the findings are confirmed, that would lend strong support for the emerging consensus about Mars’ history: that the planet once had oceans, rivers and lakes where life could have taken root – but that virtually all of the water froze up or disappeared billions of years ago, when much of Mars’ atmosphere was stripped away. There might have been only a relatively short window for Martian life to thrive.

The best way to confirm the findings would be to analyze Martian rocks on the ground. The researchers point out that the regions they studied are relatively close to the site where the Mars Pathfinder probe landed back in 1997, and could easily be accessed by future landers.

“Some of the tsunami deposits might be prime astrobiological targets,” said co-author Alberto Fairen, a research scientist at the Center for Astrobiology in Spain and a visiting scientist at Cornell University.

In addition to Rodriguez, Fairen and Platz, the authors of “Tsunami Waves Extensively Resurfaced the Shorelines of an Early Martian Ocean” include Kenneth Tanaka, Mario Zarroca, Rogelio Linares, Goro Komatsu, Hideaki Miyamoto, Jeffrey Kargel, Jianguo Yan, Virginia Gulick, Kana Higuchi, Victor Baker and Natalie Glines.

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