We’re pretty certain Mars once had a lot of water, in the form of a large ocean in the northern hemisphere of the planet. But scientists have long been puzzled by the lack of any noticeable evidence for this ancient body of water, particularly a coastline, a feature common around Earth’s seas.
That mystery may have now been solved by a remarkable new study. Published in Nature Scientific Reports, a team led by Alexis Rodriguez from the Planetary Science Institute in Arizona has found evidence for two ancient mega-tsunamis on Mars. These huge walls of water, and we mean huge, would have spread sediment across Mars, washing away any evidence of a coastline.
“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,” Rodriguez said in a statement. “Our discovery offers a simple solution to this problem; widespread tsunami deposits distributed within a wide range of elevations likely characterize the shorelines of early Martian oceans.”
The cause of these tsunamis would have been two asteroid impacts separated by a few million years, forming impact craters at the bottom of the ocean about 30 kilometers (18 miles) in diameter. The resulting tsunamis from the impacts would have been up to 120 meters (400 feet) high. When each wave reached the shore, it would have formed “tendrils” (called lobes) stretching as long as 250 kilometers (155 miles).
Shown is one of the proposed tendrils, or “lobes,” on Mars. Alexis Rodriguez
“Imagine this enormous red wave coming towards you, up to 120 meters high,” Rodriguez told Nature. “It would have been pretty spectacular.”
The first tsunami would have spread rocks far from the original shoreline, but by the time of the second tsunami, rapid climate change on Mars would have already turned much of the water into ice. As a result, the second tsunami would have transported water-ice, traveling like an icy slurry.
Interestingly, it could be possible for future landers to study these deposits, with the latter potentially containing frozen samples of Mars’ ancient ocean. That’s a rather tantalizing prospect for anyone hoping to go to Mars.
Evidence for these ancient tsunamis comes from ground imagery and thermal imagery of two regions in the northern plains of Mars, circum-Chryse and north-western Arabia Terra. This allowed the researchers to estimate two proposed shoreline levels on early Mars 3.4 billion years ago (in the image below).
Above, the proposed shoreline levels of early Mars. Alexis Rodriguez
What’s more, though, the researchers think these weren’t the only two events that may have reshaped the shorelines of Mars’ ancient ocean (which disappeared as the Martian atmosphere was lost). Mega-tsunamis from other impacts, or even huge landslides or Martian earthquakes, could also have played a part in hiding the remains of the ocean from our view.
“As a follow-up investigation we plan to characterize these terrains and assess their potential for future robotic or human in-situ exploration,” Rodriguez added in the statement, raising the exciting prospect that future missions – manned or unmanned – could directly sample one of these regions.
Perhaps most excitingly of all is the thought that one of these regions may be the best area to search for ancient life on Mars. In particular, the icy chunks could contain frozen biosignatures from its briny ocean. Planetary exploration rules currently forbid spacecraft from exploring such regions due to risks of contamination, but one would hope there might be a bit of leeway in the future, particularly if this theory is confirmed.
Shown is a representation of how far these Martian mega-tsunamis would have traveled on Earth. Alexis Rodriguez