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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 images taken from the ground showed a surprisingly rocky surface in the red planet’s north 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 baffled scientists, who believe an ocean once existed 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.
The catastrophic event likely occurred when an asteroid smashed into the shallow Martian ocean, 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 landing, NASA’s Mariner 9 spacecraft had orbited Mars, spotting the first landscapes on another planet that suggested evidence of ancient flood channels there.
Interest in the potential for life on the red planet led scientists to select its north equatorial region, Chryse Planitia, as the first Martian landing site for Viking I.
“The lander was designed to search for evidence of existing life on the Martian surface, so in order to select a suitable landing site, engineers and scientists at the time were faced with the arduous task of using some of the earliest images acquired. of the planet, accompanied by images based on Earth. radar survey of the planet’s surface,” lead study author Alexis Rodriguez, a senior scientist at the Institute of Planetary Sciences in Tucson, Arizona, said by email.
“The selection of the landing site had to meet a critical requirement: the presence of extensive evidence of previous surface waters. On Earth, life always requires the presence of water to exist.”
At first, scientists thought the rocky surface might be a thick layer of debris left behind as space rocks crashed into Mars, creating craters or shards of lava.
But there weren’t enough craters nearby, and lava fragments turned out to be rare on the floor of the site.
“Our research provides a new solution: that a megatsunami washed ashore, depositing sediments on which, some 3.4 billion years later, the Viking 1 lander landed,” Rodríguez said.
Researchers believe the tsunami occurred when an asteroid or comet struck the planet’s northern ocean. But finding a resulting impact crater has been difficult.
Rodríguez and his team studied maps of the Martian surface created from different missions and analyzed a newly identified crater that appeared to be the likely impact point.
The crater is 68 miles (almost 110 kilometers) wide in part of the northern lowlands, an area once likely covered by ocean. The researchers simulated collisions in this region using models to determine what impact was necessary to create what is known as Pohl crater.
It was possible in two different scenarios, one caused by a 9 kilometer (5.6 mile) asteroid encountering strong ground resistance and releasing 13 million megatons of TNT energy, or a 2.9 kilometer (1.8 mile) asteroid miles) crashing into softer ground and releasing 0.5 million megatons of TNT energy.
For perspective, the most powerful nuclear bomb ever tested, bomb czarcreated 57 megatons of TNT energy.
During simulations, both impacts created a crater the size of Pohl, as well as a megatsunami that came within 932 miles (1,500 kilometers) of the impact site.
The 1.8-mile asteroid generated a tsunami measuring 820 feet (250 meters) in height once it made landfall.
The results were similar to those of the Chicxulub impact on Earth, which created a crater that was initially 62 miles (100 kilometers) wide and unleashed a mighty tsunami that went around the world.
The impact likely sent water vapor into the atmosphere, which would have affected Martian weather and could have created snow or rain in the fallout. Large amounts of shallow ocean water, as well as sediment, would have been displaced, Rodríguez said, although most of the water returned to the ocean shortly after the megatsunami peaked.
“The seismic shaking associated with the impact would have been so intense that it could have dislodged materials from the seafloor in the megatsunami,” said study co-author Darrel Robertson at NASA Ames Research Center in Silicon Valley, California, in a statement. .
It is also possible that the megatsunami has reached the place where it landed in 1997 the Pioneersouth of where Viking 1 landed, and even contributed to the formation of an inland sea.
If so, then the two modules landed on the site of ancient marine environments.
“The ocean is thought to have been fed by groundwater from aquifers that likely formed much earlier in Martian 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 investigate Pohl crater as a potential landing site for a future rover, as the location could contain evidence of ancient life.
“Immediately after its formation, the crater would have generated submarine hydrothermal systems that lasted for tens of thousands of years, providing energy and nutrient-rich environments,” Rodríguez said, referring to the heat generated by the asteroid impact.