Discovering that the fall of an asteroid several kilometers in diameter caused a huge tsunami is generally not good news. Except perhaps in the case of Mars, a fascinating planet about which scientists are always trying to find out more.
We have known for some time now that Mars was probably not always the arid planet whose robotic explorers transmit images to us today. The scientists who study it are also constantly looking for traces of the water that would once have been present on the planet. This time around, they weren’t disappointed: new research, published in Scientific Reportstend to demonstrate that a giant asteroid would have once caused a gigantic tsunami.
The asteroid in question would have been comparable in size to the one that hit Earth 66 million years ago, causing a mass extinction and turning the page on the dinosaurs forever. How do they know, then? In reality, the researchers located a huge crater which gave them a clue. They named him Pohl. However, this dear Pohl is located in an area that has already been studied in the 1970s. Scientists had already concluded that there must have been a great flood here, possibly on the edge of an ocean.
The fall of an asteroid in the area could therefore explain the famous flood. In fact, the possibility had already been explored. Viking 1, NASA’s first explorer robot, had already landed on Mars near this area in 1976. It had found a plain strewn with rocks, which was not necessarily characteristic of a flooded area. In 2016, a research team led by Alexis Rodriguez of the Planetary Science Institute in Arizona took a closer look. They had deduced that it could be the result of a tsunami.
At that time, the team hypothesized that two tsunamis were triggered by separate impact events. One would have been 3.4 billion years ago, while the other would have taken place 3 billion years earlier. Thanks to numerical simulations, they had identified the Lomonsov crater as the source of the last tsunami. However, the origin of the first still remained obscure.
Two possible hypotheses for the creation of Pohl
Alexis Rodriguez and his team therefore continued to comb through Martian craters, and eventually met Pohl. It is located approximately 900 kilometers northeast of the Viking 1 landing site. This crater is 110 kilometers in diameter, and is located approximately 120 meters below what scientists believe to have been sea level, in a region called Chryse Planitia.
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By analyzing the age of the rocks around Pohl, they were able to date them to 3.4 billion years ago, suggesting that Pohl may also have formed during this period. His position, too, made him a good suspect for the tsunami. The scientists therefore sought to confirm their hypotheses by running impact simulations on a computer program. Two scenarios make possible the formation of the crater and the resulting tsunami.
- First case : an asteroid 9 km in diameter would have fallen on Mars, and would have encountered strong resistance on the ground, causing an explosion of 13 million megatons. Note that a megaton is a unit of energy that corresponds approximately to the amount of work released by the explosion of one million tons of trinitrotoluene (TNT). What, indeed, create a beautiful crater.
- Second case: an asteroid “only” 3 kilometers in diameter would have crashed into Mars, but encountered low ground resistance, releasing 0.5 million megatons of TNT energy.
In both cases, the impact would have created the famous crater 110 kilometers in diameter. It would have been able to cause a huge tsunami, which could have traveled up to 1500 km from the point of impact. These two hypotheses stick with the flood zone already studied, but also with the landscape strewn with rock which had been discovered by Viking 1. The impact of the asteroid would indeed have generated ejecta, which would then have been transported by the tsunami wave.
« Our megatsunami momentum generated by the simulated impact closely matches the margins of the mapped older megatsunami deposit and predicts fronts reaching the Viking 1 landing site. write the researchers. Since this impact took place in a marine environment, it is in fact quite similar to the one that took place on Earth, in the Chicxulu crater, which we mentioned at the beginning of this article.
« Our discoveries “, they write, “ confirm that the rocks and soil salts at the landing site are of marine origin, prompting scientific reconsideration of the information gathered from the first in situ measurements on Mars ».