Two massive tsunamis may have rocked Mars when the planet was covered with oceans billions of years ago, according to a new study. The tsunamis may have been caused by meteorite impacts, researchers say. And signs of their passing provide the latest evidence that Mars was a wet planet full of water eons ago — water that may have supported some form of life.

Today, Mars is a barren and dry environment, with an average frigid temperature of -80 degrees Fahrenheit. But many scientists think that, billions of years ago, the Red Planet was covered by liquid water. One mystery was never solved, however: if Mars once had oceans, how come scientists haven't been able to identify the shorelines formed by waves? Today's study, published in the journal Scientific Reports, is one piece of the puzzle to answer that question.

"Our paper provides very solid evidence for the existence of very cold oceans on early Mars," Alberto Fairén, an astronomer at Cornell University and a co-author of the study, said in a statement. "It is difficult to imagine Californian beaches on ancient Mars, but try to picture the Great Lakes on a particularly cold and long winter, and that could be a more accurate image of water forming seas and oceans on ancient Mars."

The researchers estimate that the two massive tsunamis occurred about 3.4 billion years ago. The first one inundated an area of more than 300,000 square miles and the second, which likely took place a few million years later, affected an area of nearly 400,000 square miles. Both were caused by two large meteorites that crashed into Mars.

The scientists found the evidence for these cataclysmic events by using geographical and thermal images of the planet's surface. They found "lobes" — mounds of rock debris that could have been formed only by a forceful flow of water. The boulders are hundreds of miles long and wide. "Tsunamis are the most, if not the only, fitting explanation for these observations," lead author Alexis Rodriguez, a researcher at the Planetary Science Institute, told The Washington Post. "There are not many processes in nature that can form these features."

But the striking observation is that the piles of rock debris from the two tsunamis suggest that Mars underwent frigid climate change between the two meteorite impacts. In that period of time, the planet's water began freezing and the shorelines receded. The lobes formed by the second tsunami seem to be rich in ice. "These lobes froze on the land as they reached their maximum extent and the ice never went back to the ocean, which implies the ocean was at least partially frozen at that time," Fairén said.

If microbial life was indeed present in the ancient Martian ocean, it could have been "trapped" inside those frozen piles of debris and that's where we could find traces of it still today. "Cold, salty waters may offer a refuge for life in extreme environments, as the salts could help keep the water liquid," Fairén said. "If life existed on Mars, these icy tsunami lobes are very good candidates to search for biosignatures."

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