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When NASA’s Viking 1 lander made history as the first spacecraft to reach Mars on July 20, 1976, it sent back images of a landmark no one expected.
Those first images taken from Earth showed a surprising rock-strewn surface in the red planet’s northern equatorial region, where flat plains and floodplain rivers are expected based on images of the area taken from space.
The mystery of the Viking harbor site has long puzzled scientists, who believe that a sea once existed there.
Now new research suggests that Mars may have touched down where the megatsunami deposited the material 3.4 billion years ago, according to a study published Thursday in the journal Scientific Reports.
The catastrophic event likely occurred when an asteroid slammed into the shallow Martian ocean — similar to the Chicxulub asteroid impact that wiped out the dinosaurs on Earth 66 million years ago, according to researchers.
Five years before Viking’s landing, NASA’s Mariner 9 spacecraft had orbited Mars, spotting the first landscapes on another planet that suggested evidence of ancient flood canals.
The study of the potential for life on the Red Planet prompted scientists to choose its northern equatorial region, the Chryse Plain, as the first Mars site for Viking I.
“Deventor is designed to search for evidence of life on the Martian surface, to choose a suitable port, engineers and scientists at the time have a difficult task to use some of the first images of the planet acquired with Earth-based radar to scan the surface of the planet,” said lead study author Alexis Rodriguez, senior scientist at the Planetary Science Institute in Tucson, Arizona, via email.
“The selection of a landing site is necessary to fulfill a critical requirement – the presence of ample evidence of upper surface water. On earth, life always requires the presence of water to exist.
At first, scientists thought that the rocky surface was a dense layer of debris left behind by space rocks crashing into Mars and creating craters, or broken pieces of lava.
But there weren’t enough craters nearby, and fragments of lava proved to be a rare location on the ground.
“The research offers a new solution – a megatsunami washing the beach, mimicking the sediments that, about 3.4 billion years later, would have touched the landing of Viking I,” said Rodriguez.
Researchers believe that tsunamis occur when asteroids or comets hit the Northern Ocean. But the result of the discovery of the crater was difficult.
Rodriguez and his team studied maps of the Martian surface created from different missions and analyzed a newly identified crater that seemed likely to be the impact point.
The crater is 68 miles (almost 110 kilometers) in the northern part of the plain — an area once likely covered by an ocean. Researchers in this region simulated collisions using sketches to determine what impact was necessary to create what is known as the Pohl Crater.
It could be done in two different scenarios, one with an asteroid encountering a 5.6-mile (9-kilometer) firm resistance and releasing 13 million megatons of TNT energy, or a 1.8-mile (2.9-kilometer) asteroid plowing into softer ground and 0.5 million megatons of TNT paying energy
For perspective, the most powerful nuclear bomb ever tested, the Tsar Bomba, created 57 megatons of TNT energy.
According to the simulations, each impact created a crater with the dimensions of Pohl — as well as a megatsunami that created 932 miles (1,500 kilometers) from the impact site.
The 1.8-mile asteroid generated a tsunami that was 820 feet (250 meters) long once it reached the ground.
The results were similar to those of the Chicxulub impact on Earth, which initially moved the crater 62 miles (100 kilometers) and triggered a massive tsunami that traveled around the globe.
The impact likely sent water vapor into the atmosphere that would have affected the Martian sky and potentially created snow or rain in the fallout. Most of the water returned to the ocean soon after the peak of the megatsunami, Rodriguez said.
“The seismicity associated with the impact would have been so violent that it could have pushed sea materials in a megatsunami,” said study co-author Darrel Robertson at NASA’s Ames Research Center in California’s Silicon Valley, in a statement.
It is also possible that the megatsunami reached the site in 1997 at Pathfinder, south of where Viking 1 landed, and also contributed to the formation of the Mediterranean Sea.
If so, the two descendents have reached a location in the ancient marine environment.
“The ocean is thought to have been fed by ground water aquifers that formed much earlier in Martian history – over 3.7 billion years ago,” when the planet was a primordial “land” with rivers, lakes, seas and oceans. Roderic said.
Next, Pohl’s team wants to investigate the crater as a potential site for future pirate routes, as the site may contain evidence of ancient life.
“Right after its installation, the crater would have generated underwater hydrothermal systems lasting tens of thousands of years, providing energy and nutrient-rich environments,” Rodriguez said, referring to the heat generated by the impact of the asteroid.
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