When NASA’s Viking 1 lander made history as the first spacecraft to touch down on Mars on July 20, 1976, it sent back images of a landscape no one was expecting. Those first images taken from the ground there showed a surprisingly boulder-strewn surface in the red planet’s northern equatorial region, rather than the smooth plains and flood channels expected based on images of the area taken from space.
The mystery of the Viking landing site has long puzzled scientists, who believe an ocean once existed there. Now, as CNN reports, new research suggests that the lander touched down where a Martian megatsunami deposited materials 3.4 billion years ago, according to a study published Thursday in the journal Scientific Reports.
According to CNN, the catastrophic event likely occurred when an asteroid slammed into the shallow Martian ocean — similar to the Chicxulub asteroid impact that wiped out dinosaurs on Earth 66 million years ago, according to researchers.
Five years before the Viking I landing, NASA’s Mariner 9 spacecraft had orbited Mars, spotting the first landscapes on another planet that suggested evidence of ancient flood channels there. The interest in the potential for life on the red planet prompted scientists to select its northern equatorial region, Chryse Planitia, as the first Martian landing site for Viking I.
At first, scientists thought the rocky surface might be a thick layer of debris left behind due to space rocks crashing into Mars and creating craters, or broken pieces of lava. But there weren’t enough craters nearby, and lava fragments proved rare on the ground at the site. “Our investigation provides a new solution — that a megatsunami washed ashore, emplacing sediments on which, about 3.4 billion years later, the Viking 1 lander touched down,” states lead study author Alexis Rodriguez, senior scientist at Arizona’s Planetary Science Institute.
The researchers believe the tsunami occurred when an asteroid or comet hit the planet’s northern ocean. But finding a resulting impact crater has been difficult. Rodriguez and his team studied maps of the Martian surface created from different missions and analyzed a newly identified crater that seemed to be the likely point of impact.
The crater is 68 miles (nearly 110 kilometers) across in part of the northern lowlands — an area once likely covered in ocean. Researchers simulated collisions in this region using modeling to determine what impact was necessary to create what’s known as the Pohl crater. During simulations, impacts created a crater with Pohl’s dimensions — as well as a megatsunami that reached 932 miles (1,500 kilometers) from the impact site.
“The seismic shaking associated with the impact would have been so intense that it could have dislodged sea floor materials into the megatsunami,” said study coauthor Darrel Robertson at NASA’s Ames Research Center in California’s Silicon Valley, in a statement.
It’s also possible that the megatsunami reached the location of the 1997 landing site for the Pathfinder, south of where Viking 1 landed, and even contributed to the formation of an inland sea. If so, then the two landers touched down at the site of ancient marine environments.
“The ocean is thought to have been groundwater-fed from aquifers that likely formed much earlier in Martian history — over 3.7 billion years ago — when the planet was ‘Earth-like’ with rivers, lakes, seas, and a primordial ocean,” Rodriguez said.
Next, the team wants to investigate Pohl crater as a potential landing site for a future rover, since the location might contain evidence of ancient life.
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