Scientists Believe Asteroid Strikes Created Massive Ancient Martian Tsunamis
When you look at the surface of Mars, what do you see?
It's cold and dry. Rocky and sandy.
A dry planet. A desert planet.
But there is a great deal of evidence that ancient oceans once covered the northern plains when the planet was relatively young.
A cold, salty, icy ocean.
Many people will debate that point -- after all, to date there has been a lack of real, direct evidence -- but new thermal images of the northern plains reveal what appear to be ancient shorelines.
In a paper published by Scientific Reports (a publication of the journal Nature) on May 19, Alberto Fairén, a planetary scientist at the Center of Astrobiology in Madrid and Cornell University in New York, asserted:
Our work provides definitive evidence for the presence of large and long-lived oceans on Mars.
But what may be even more interesting is that it looks like the shorelines of these oceans went through traumatic changes from two massive meteorite strikes about 3.4 billion years ago.
As team of scientists consisting of Fairén and co-lead Alexis Rodriguez of the Planetary Science Institute, along with 12 others, examined these shorelines for anomalies, they discovered large "lobes" of sediment and rock that provide clear evidence of massive water flows running down into the plains of Chryse Planitia and Acidalia Planitia.
Similar lobes are seen on Earth after tsunamis reach a shoreline, but the lobes on Mars are much, much bigger.
It's that size, as well as the shape, that convinced these scientists that two large meteorites -- hitting the planets millions of years apart -- triggered a pair of ancient Martian tsunamis that forever reshaped the landcape.
The first tsunami flooded an area about 309,000 square miles (800,000 square kilometers) in size and dragged boulders up to about 33 feet (10 meters) along with it.
As the Martian tsunamis receded, the water carved numerous channels, similar to what you see after tsunamis here on earth, ranging between up to about 655 feet (200 m) wide and about 12.4 miles (20 km) long.
As Fairen said:
About 3.4 billion years ago, a big meteorite impact triggered the first tsunami wave. This wave was composed of liquid water. It formed widespread backwash channels to carry the water back to the ocean,.
These "backwash" channels are clearly evident as you look at the terrain just north of Valles Marineris on up to Chryse Planitia.
But then, a few million years later, a second meteorite hit ...
This second event was even larger than the first, inundating an area of about 386,000 square miles (1 million sq. km) large.
And it showed something else, as well.
Over the course of time between the two asteroid strikes, Mars had cooled significantly. The oceans had frozen -- and receded -- from their previous shorelines. As Fairen said:
The ocean level receded from its original shoreline to form a secondary shoreline, because the climate had become significantly colder.
How do they know?
The second mega-tsunami deposited large "lobes" of sediment and rock just like the first, but these lobes contained something else -- ice.
According to Fairén:
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. Our paper provides very solid evidence for the existence of very cold oceans on early Mars.
According to Fairen, even after the tsunami receded, these lobes retained their boundaries and shapes, suggesting the frozen ancient ocean was briny.
But don't think of these shorelines as the sunny ocean beaches you might see here on Earth. Instead, consider the cold, icy images of the Great Lakes in America in winter.
As Fairen added:
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.
But that may have be a very good thing...
The salt may have kept the water from completely freezing and actually provided a safe incubator for life.
Which makes these areas a prime spot for future research.
As Alexis Rodriguez pointed out:
We have already identified some areas inundated by the tsunamis where the ponded water appears to have emplaced lacustrine sediments, including evaporites. As a follow-up investigation we plan to characterize these terrains and assess their potential for future robotic or human in-situ exploration.
If life existed on Mars, these icy tsunami lobes are very good candidates to search for biosignatures.
But it's not just the potential for life that has these scientists excited. They are also exploring the possibility that some tsunamis may have struck glacier-rimmed shores, knocking off chunks of ice that would have drifted unimpeded in the ancient coastal waters. In other words ...
That's right - icebergs. As Fairen concluded:
We have some preliminary evidence for such a process, so stay tuned.
We definitely will.
The full paper can be found here:
Rodriguez, J. A. P. et al. Tsunami waves extensively resurfaced the shorelines of an early Martian ocean. Sci. Rep. 6,25106; doi: 10.1038/srep25106 (2016).