The ocean waves were almost as tall as Egypt's Great Pyramid of Giza, and they barreled across the red planet. Today, a team of scientists has announced the first discovery of extraterrestrial tsunamis.

A team of astronomers and geologists led by J. Alexis Rodriguez at the Planetary Science Institute in Tucson, Arizona has uncovered evidence of massive tsunamis on Mars billions of years ago. As Rodriguez reports, two separate megatsunamis tore across the red planet around 3.4 billion years ago, a time when Mars was a mere 1.1 billion years old and nearby Earth was just cradling its first microbial lifeforms. The two tsunamis created 150-foot-high shore-break waves on average, and some absolutely monster waves up to 400 feet tall. Rodriguez and his colleagues outline their tsunami findings today in the journal Scientific Reports.

The scientists say the Martian tsunamis were triggered by meteor impacts, which crashed into Mars' ancient water-oceans and "generated marine impact craters approximately [19 miles] in diameter," says Thomas Platz, a geologist with the team who specializes in crater formation. The two tsunamis took place millions of years apart, although they were set off by separate impacts of roughly similar size.

Extraterrestrial Tsunamis

Visible light images showing older tsunami lobate upper reaches (white arrows) that embay local highland hills. The image below reveals the deposit's bouldery substrate. Up is towards the bottom right of the images. A. Rodriguez

Just like their brethren on Earth, Martian tsunamis would have washed sediments and boulders hundreds of miles inland and carved unique geologic features into the landscape. For example: These disasters could etch backwash water channels as they receded back into the ocean. But after 3.4 billion years of weathering and erosion, such geologic fingerprints are not easy to spot.

Rodriguez and his colleagues stumbled across evidence of these tsunamis while scouring over images of Mars' relatively flat northern planes. Two regions called Chryse Planitia and Arabia Terra. Using detailed infrared maps rendered by the thermal camera on the 15-year-old Mars Odyssey orbiter, the scientists identified the high water marks of the tsunamis—features that look a lot like ancient ocean coastlines. The team found thermally bright, rocky, and boulder-rich exposures that bordered dark and flat sediment layers perched on a slightly higher elevation. That bright rocky exposure was churned up by the tsunami billions of years ago, where the dark swath stayed dry.

Behind these high water marks are remnants of backwash channels carved by the retreating water. Tellingly, each of these channels juts directly backwards from the temporary shorelines. Behind the rubble, shorelines, and channels left by the tsunamis, Rodriguez's team found seven different meteoroid impact craters, each one of which might have set off the monolithic waves.

Here's the picture all that geologic data painted: The first tsunami stormed across 300,000 square miles of Mars, and smashed inland about 320 miles. The second tsunami rolled across a far larger swath of red soil, almost 400,000 square miles, and traveled further inland as well, more than 400 miles. Compare that to Earth's devastating 2004 Indian Ocean tsunami, which traveled 1.4 miles inland at its farthest and reached a maximum of 65 feet in height.

Life-Bringing Waves?

Perhaps counterintuitively, that second Martian tsunami didn't travel farther across the Red Planet than the first because it was more powerful event caused by a larger meteorite. Rather: "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," Rodriguez says. Because of this, the waves rolled across a Martian surface that had significantly eroded and smoothed, and that smoothness let the unhindered waves travel farther.

The scientists also say that second tsunami might have thrown slushy, icy boulders across the Martian landscape. Strangely enough, that could have big implications for scientists' hunt for life on the red planet.

"In spite of the extremely cold and dry global climatic conditions, the early Martian ocean likely had a briny composition that allowed it to remain in liquid form for as long as several tens of millions of years. Subfreezing briny aqueous environments are known to be habitable environments on Earth, and consequently, some of the tsunami deposits might be prime astrobiological targets," says Alberto Fairén, a research scientist with the team at the Center for Astrobiology in Spain. In other words, the slushy, salty chunks of ice thrown by the tsunami could have created long-lasting tidal pools perfect for primordial life.

"We have already identified some areas inundated by the tsunamis where the ponded water appears to have [been formed by this ice.] As a follow-up investigation we plan to characterize these terrains and assess their potential for future robotic or human exploration," Rodriguez says.

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