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Viking 1 may have landed at the site of an ancient Martian megatsunami

Viking 1 may have landed at the site of an ancient Martian megatsunami

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When NASA’s Viking 1 lander made history as the first spacecraft to land on Mars on July 20, 1976, it sent back images of a landscape no one expected.

Those first ground-based images surprisingly showed a rock-strewn surface in the red planet’s northern equatorial region, rather than the smooth plains and flood channels expected from images of the area taken from space.

The mystery of the Viking landing site has long puzzled scientists who believe there was once an ocean there.

Now, new research suggests the lander landed where a Martian megatsunami deposited materials 3.4 billion years ago, according to a study published Thursday in the journal Scientific Reports.

A catastrophic event probably occurred when an asteroid hit the shallow ocean of Mars – similar Chicxulub asteroid impact which wiped out the dinosaurs on Earth 66 million years ago, according to researchers.

Five years before Viking I landed, NASA’s Mariner 9 spacecraft orbited Mars, spotting the first landscapes on the second planet that pointed to evidence of ancient flood channels.

Interest in the red planet’s potential for life prompted scientists to select its northern equatorial region, Chryse Planitia, as the first landing site on Mars for Viking I.

“The lander was designed to look for evidence of life on the surface of Mars, so engineers and scientists at the time were faced with the difficult task of using some of the earliest images of the planet, selecting a suitable landing site, and conducting a radar survey of the planet’s surface,” lead study author Alexis Rodriguez, a senior scientist at the Institute for Planetary Sciences in Tucson, Arizona, said via email.

“The selection of the landing site was necessary to fulfill a critical requirement — the presence of extensive evidence of former surface water. On Earth, life always requires the presence of water.”

At first, scientists thought the rocky surface might be a thick layer of debris left behind by space rocks that crashed into Mars and created craters, or broken pieces of lava.

But there were not enough craters nearby, and lava fragments proved to be rare on the ground at that location.

“Our investigation provides a new solution – that a megatsunami washed ashore, dumping the sediments on which, about 3.4 billion years later, Viking 1 landed,” Rodriguez said.

Researchers believe that the tsunami occurred when an asteroid or comet hit the planet’s northern ocean. But the crater that followed was hard to find.

Rodriguez and his team studied maps of the Martian surface made by various missions and analyzed a newly identified crater that appeared to be the likely impact site.

The crater is 68 miles (almost 110 kilometers) wide in part of the northern lowlands—an area that was once likely covered by the ocean. Researchers simulated collisions in this region using modeling to determine what impact was necessary to create what is known as Pohl Crater.

This was possible in two different scenarios, one caused by a 5.6-mile (9-kilometer) asteroid that encountered strong ground resistance and released 13 million megatons of TNT energy, or a 1.8-mile (2.9-kilometer) asteroid that plowed into the softer ground and released 0.5 million megatons of TNT energy.

In perspective, the most powerful nuclear bomb ever tested, Tsar Bombait created 57 megatons of TNT energy.

During the simulations, both vessels created a crater of Pohl dimensions—as well as a megatsunami that reached 932 miles (1,500 kilometers) from the impact site.

The 1.8-mile asteroid caused a tsunami that reached land 250 meters high.

The results were similar to those of the Chicxulub impact on Earth, which created a crater that was initially 62 miles (100 kilometers) across and caused a great tsunami that went around the world.

The impact likely sent water vapor into the atmosphere, which would affect the Martian climate and potentially create snow or rain in precipitation. Huge amounts of water from the shallow ocean, as well as sediments, would have been displaced, Rodriguez said, although most of the water returned to the ocean shortly after the megatsunami reached its peak.

“The seismic shaking associated with the impact would have been so intense that it could have dislodged seafloor materials in a megatsunami,” said study co-author Darrel Robertson of NASA’s Ames Research Center in California’s Silicon Valley.

It is also possible that the megatsunami reached the landing site in 1997 Pathfindersouth of where Viking 1 landed, and even contributed to the formation of the inland sea.

If so, then two landers landed on the site of ancient sea environments.

“The ocean is thought to have been fed by groundwater from aquifers that likely formed much earlier in Mars’ history — more than 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 explore Pohl Crater as a potential landing site for a future rover, since the site could contain evidence of ancient life.

“Immediately after formation, the crater would have created submarine hydrothermal systems that would have lasted for tens of thousands of years, providing an environment rich in energy and nutrients,” Rodriguez said, referring to the heat produced by the asteroid impact.



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