Supersized tsunamis once roiled an ocean on Mars, scientists say
Mars might have been a wilder water world than we thought. Scientists scanning the Martian terrain say they have discovered signs of two massive tsunamis in the northern hemisphere — events that might have been caused by massive, crater-carving impacts.
The findings, described in Thursday’s edition of the journal Scientific Reports, bolster the idea that Mars once held an enormous ocean and depict a Red Planet that was far more dynamic than previously believed.
Mars may look dry and dead today, but it seems to have been much more Earth-like in the distant past, with a thick atmosphere and large bodies of standing water. Some evidence even suggests that our arid neighbor may have had a major ocean about 3.4 billion years ago.
That idea hasn’t been universally embraced, however. In part, that’s because scientists haven’t been able to find a steady, continuous boundary in the terrain that would demarcate an ancient body of water.
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“What a lot of people were doing in the past was to look for shorelines distributed along constant elevations, which is what we see here on Earth,” said study leader J. Alexis P. Rodriguez, a senior scientist at the Planetary Science Institute in Tucson.
Rodriguez took a different approach. Several years ago, he decided to look instead for signs of tsunamis, which could occur only if an ocean were present.
And he found them — in the form of several lobe-shaped deposits of debris in the northern part of the planet. These lobes had been spotted before, but their geological significance had remained unsettled.
Most of the time, these lobes of material indicate that water was pushing debris forward. Since water flows from high to low ground, the lobes usually point downward.
Strangely, these ones pointed up, against gravity’s pull.
Aside from tsunamis, “there’s not too many other processes that can form lobate, landward deposits,” said study co-author Virginia Gulick, a planetary scientist at the NASA Ames Research Center and the SETI Institute. “A tsunami deposit is like a flood deposit; it’s just in the reverse direction.”
Using data from three NASA spacecraft — the Mars Odyssey thermal imager, cameras aboard the Mars Reconnaissance Orbiter and the Mars Global Surveyor’s laser altimeter — the researchers were able to assemble a map of certain regions in the northern plains that allowed them to analyze how these strange shapes came to be.
They found that two massive tsunamis raged through the area, probably within a few million years of each other; the first washed over an area of about 800,000 square kilometers and the second swamped an area of roughly 1 million square kilometers.
The typical wave height as the water hit the shore would have likely been about 50 meters but, at various locations, could have ranged anywhere from 10 to 120 meters or so. That’s far taller than the 39-meter wave that hit Japan after the 9.0 Tohoku earthquake in 2011.
What could have caused such a massive wave? The scientists have a guess: a space-borne missile such as an asteroid or comet smashing into the planet. An impact capable of moving mountains of water would have left a crater at least 30 kilometers across — and the scientists on Rodriguez’s team said they found about 23 such “marine impact craters” in the region near the debris lobes.
Of course, it’s just a hypothesis for the moment, because they can’t match a particular crater to one of the events. But their story makes sense, given that similar things have happened on Earth: The asteroid that killed the dinosaurs some 66 million years ago launched a massive tsunami as well.
“To see these types of events that we’re familiar with on Earth and to see similar features on Mars is really exciting,” said Lisa Ely, a geologist at Central Washington University who studies tsunamis on Earth and was not involved in the research. “There’s no reason to think Earth is the only dynamic planet out there.”
The findings also explain why scientists can’t seem to find continuous shorelines: The tsunamis buried them.
The two tsunamis also left very different marks on the Martian terrain, the researchers said. The first wave deposited loads of boulders in the lobes and gouged deep channels as the water washed back toward the ocean; these channels are also seen around marine impact craters on Earth.
The second occurred during a colder period in the planet’s history and carried an ice-rich slurry past the shoreline. If there was life in this ancient ocean, those icy deposits left by the second tsunami might be a prime place to look, Rodriguez said.
NASA’s 1997 Mars Pathfinder mission landed not too far from these lobes, he added, which means that future rovers looking for signs of life could potentially land safely near the tsunami scars.
Whether this evidence exists at all and survives to this day is another matter entirely, of course.
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UPDATES:
May 20, 10:30 a.m.: This story has been updated throughout with additional information.
