Images: NASA/JPL, Goto et al.
A long time ago, a huge asteroid struck a watery planet in our solar system, sparking an enormous megatsunami that reached hundreds of feet into the air and left permanent traces on the landscape.You might be picturing the famous space rock that wiped out the dinosaurs on Earth, but scientists have now confirmed that the same story played out on Mars some 3.4 billion years ago, at a time when Mars hosted a huge ocean that might have hosted microbial life.
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After decades of speculation about this ancient extraterrestrial impact and megatsunami, researchers led by Alexis Rodriguez, a senior scientist at the Planetary Science Institute, have pinpointed the likely spot, called Pohl crater, where the asteroid collided with the Martian ocean at roughly 24,000 miles per hour. This key discovery suggests that Pohl crater, and its surrounding regions, could be important targets in the search for alien life, as they may bear “information on how the ocean’s habitability and possible life evolved,” according to a study published in Scientific Reports on Thursday. The team was also able to reconstruct some of the mind-boggling effects of this ancient impact and the subsequent megatsunami, which may have produced 800-foot-high waves. “If we were standing here and this impact happened, we would have been tossed up in the air, literally tens or hundreds of meters,” Rodriguez said in a call with Motherboard. “It’s basically like jumping on a trampoline.” “Marine craters on Mars are obviously very important because you have, basically, an impact that forms into an ocean,” he continued. “You have hydrothermal systems that would have formed after the impact, and that has habitability and paleoenvironmental implications.”
To that point, the new study also revives a tantalizing mystery about Martian life that dates back to NASA’s Viking 1 lander, which was the first mission to operate on the surface of Mars in 1976. The lander found strange compounds at its landing site that some scientists believe could indicate life, but the evidence has remained controversial for decades.Now, Rodriguez and his colleagues have demonstrated that Viking 1 actually sits in the remains of the ancient megatsunami—a promising area to look for life—adding a new layer of intrigue to this longstanding question about the mission’s findings.“What we did in this study is to reconcile orbital data with in situ observations to show that the [Viking 1] landing site is likely a megatsunami deposit,” Rodriguez said. “In other words, you could say that like the first images that we found the surface of Mars, through NASA's first successfully operating spacecraft, were of a marine-related process: a megatsunami deposit. So, there's a historical relevance there.” “These marine deposits that were transported by the wave could have evidence of what kind of salts existed in the ocean and what kind of sediments dominated the stratigraphy of that particular region,” he continued. “There could be a lot of information that is interesting to understand about early Mars, but most importantly, I think, is the fact that we already landed there nearly 50 years ago.”
Indeed, the story of this ancient megatsunami dates back to the dawn of the space age, when these enormous signs of ancient catastrophic floods on Mars were captured in more detail by early interplanetary missions. Viking’s landing site was selected precisely because these dried-up channels seemed like a prime destination to look for life. In 2019, scientists, including Rodriguez, were able to identify another impact crater, called Lomonosov, that produced another megatsunami in the same region about three billion years ago. While the remains of the older megatsunami were clearly observable, Rodriguez and his colleagues had to painstakingly examine the Martian landscape to find a crater that matched the age of this flood. The search had to rule out buried craters that were older than the Martian ocean, and therefore could not produce a megatsunami, while also excluding craters that were formed on top of the younger megatsunami, because these impacts occurred too late in Mars’ history. After extensive examination, Pohl crater emerged as the perfect fit for all of these parameters, opening a new window into this catastrophic event that sent Martian seawater—and any life within it—roiling for hundreds of miles across the planet. “I think that we have two distinct and very interesting astrobiological targets that come out of this study,” Rodriguez said. “The first one is obviously the Viking 1 landing site because we have this controversy so it would be good to be able to resolve it.” The second, he added, are the remains of mud volcanoes in this huge dried-up ocean basin. “There is a possibility that this mud volcanism was driven by the release of seawater trapped in the sediments, or gasses connected to the evaporation of seawater, and obviously, that has very interesting astrobiological implications,” he concluded. “So, there are lots of targets to understand the evolution of the ocean of Mars, its potential biochemistry, and the way that the environment changed within the ocean over time.”