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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 landscapes no one expected.
Those first images taken from Earth there showed a surprisingly rocky surface in the Red Planet’s northern equatorial region, rather than the smooth plains and flood channels expected based on images of the region taken from space.
The mystery of the Vikings’ landing site has long baffled scientists, who believe an ocean once existed there.
Now, new research indicates that the probe landed where the Martian megatsunami deposited material 3.4 billion years ago, according to a study published Thursday in the journal Scientific Reports.
The cataclysmic event likely occurred when an asteroid slammed into the shallow ocean of Mars — similar to the Chicxulub asteroid impact that wiped out the dinosaurs on Earth 66 million years ago, according to the researchers.
Five years before the Viking I touchdown, NASA’s Mariner 9 rover was orbiting Mars, first spotting another planet’s landscape and suggesting evidence of ancient flood channels there.
Interest in the possibility of life on the Red Planet led scientists to choose its northern equatorial region, Chryse Planitia, as the first Mars landing site for the first Vikings.
“The probe was designed to search for evidence of life on Mars, so to locate a suitable landing site, engineers and scientists at the time faced the daunting task of using some of the early images of the planet obtained, accompanied by drawings from Earth,” said lead study author Alexis Rodriguez. , senior scientist at the Planetary Science Institute in Tucson, Arizona, via email: “
“The choice of the landing site was necessary to fulfill an important requirement — ample evidence of past surface water. On Earth, life has always required water.”
At first, scientists thought the rocky surface might be a thick layer of debris left over from rocks caused by space rocks colliding with Mars and forming craters or broken lava chunks.
But there weren’t enough craters nearby, and lava fragments proved to be a rarity on Earth at the site.
“Our investigation provides a new solution – that one of the huge depths washed ashore, seeding the sediment that the Viking 1 lander landed on about 3.4 billion years later,” Rodriguez said.
Researchers believe that the tsunami occurred when an asteroid or comet hit the planet’s northern ocean. But finding a resulting impact crater has been challenging.
Rodriguez and his team studied maps of the Martian surface generated from various missions and analyzed a newly identified crater that appeared to be the likely point of impact.
The crater measures 68 miles (nearly 110 kilometers) across a portion of the northern lowlands – an area likely covered by ocean. The researchers simulated impacts in this region using modeling to determine the impact necessary to create what is known as Buhl Crater.
This was possible in two different scenarios, one caused by a 5.6-mile (9 km) asteroid that encountered strong Earth resistance and released 13 million megatons of TNT energy, or a 1.8-mile (2.9 km) asteroid colliding with a softer Earth. The release of 0.5 million megatons of TNT energy.
For perspective, the most powerful nuclear bomb ever tested, the Tsar Bomba, created 57 megatons of TNT energy.
During the simulations, both collisions created a crater of Pohl’s proportions—plus a giant tsunami that reached 932 miles (1,500 kilometers) from the impact site.
The 1.8-mile-wide asteroid triggered a tsunami of 820 feet (250 meters) as soon as it hit Earth.
The results were similar to those of the Chicxulub impact on Earth, which initially created a crater 62 miles (100 kilometers) in diameter and caused a towering tsunami that traveled around the globe.
The impact is likely to cause water vapor to rise into the atmosphere, which could affect the Martian climate and possibly cause snow or precipitation. Huge amounts of water from the shallow ocean, as well as sediment, would have gone away, Rodriguez said, although most of the water returned to the ocean shortly after the megatsunami peaked.
“The seismic vibration associated with the impact could have been so intense that it could have caused the displacement of seafloor material into the megatsunami,” study co-author Darrell Robertson of NASA’s Ames Research Center in Silicon Valley, California, said in a statement.
It’s also possible that megatsunamis reached the Pathfinder landing site in 1997, south of where Vikings 1 landed, and even contributed to the formation of an inland sea.
If so, the two craft landed at the site of ancient marine environments.
“The ocean is thought to have been fed by groundwater from aquifers that likely formed very early in Mars’ history — more than 3.7 billion years ago — when the planet was ‘Earth-like’ with rivers, lakes, seas, and a primeval ocean,” Rodriguez said.
Next, the team wants to investigate Buhl crater as a possible landing site for a future rover, as the site may contain evidence of ancient life.
“Immediately after its formation, the crater would have generated underwater hydrothermal systems lasting for tens of thousands of years, providing energy and nutrient-rich environments,” Rodriguez said, referring to the heat from the asteroid impact.
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