Giant asteroid triggered a devastating megatsunami on Mars, evidence suggests

An artist’s impression of a much wetter planet Mars 4 billion years ago. (Credits: OES/M. Kornmesser)

Translated by Julio Batista
Original by Michelle Starr for ScienceAlert

Multiple lines of evidence suggest that Mars was not always the dry dust deposit it is today.

In fact, the red planet was once so wet and muddy that a megatsunami was unleashed, hitting the landscape like a water disaster. What caused this devastation? According to new research, a giant asteroid impact, comparable to Chicxulub’s impact on Earth 66 million years ago – the one that killed off the dinosaurs.

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Researchers led by planetary scientist Alexis Rodriguez of the Institute of Planetary Sciences in Arizona, USA, located a huge impact crater that they believe is the most likely origin of the mysterious wave.

They named it Pohl and located it within an area devastated by catastrophic flood erosion, which was first identified in the 1970s, on what could be the edge of an ancient ocean.

When NASA’s Viking 1 probe landed on Mars in 1976, near a large flood channel system called Maja Valles, it found something strange: not the expected features of a landscape transformed by a megaflood, but a plain littered with boulders.

A team of scientists led by Rodriguez determined in a 2016 paper that this was the result of tsunami waves resurfacing extensively on the shores of an ancient Martian ocean.

At that time, they hypothesized that two tsunamis were triggered by separate impact events, 3.4 and 3 billion years ago. Numerical simulations led scientists to Lomonsov crater as the source of the later tsunami.

However, the origin of the previous tsunami remained elusive. The northern plains, into which a Martian ocean is believed to have spread, are full of craters and they are difficult to interpret. Rodriguez and his team scrutinized maps of the surface of Mars, looking for impact craters that could be linked to massive tsunamis.

They reached Pohl, located about 900 kilometers northeast of the Viking 1 landing site, a crater 110 kilometers in diameter, located about 120 meters below what scientists believe to be sea level, in a region called Chryse Planitia.

Topographic map showing the crater context and landing site. Image translation: Viking 1 landing site (Viking 1 Lander site), Pohl crater (Pohl crater) and Wahoo crater (Wahoo crater). (Credits: Rodriguez at al., Sci. Rep., 2022)

Based on rocks around the crater that had previously been dated to around 3.4 billion years ago, the researchers thought that Pohl may have formed around this time as well. And its position near surfaces eroded by flooding and hypothetical megatsunami deposits suggest that the crater formed during an oceanic impact.

To confirm their suspicions, the researchers performed impact simulations, adjusting the parameters of the impacting object and the surface it collided with. They found two scenarios suitable for the observed location.

First, a 9 kilometer asteroid encountering strong resistance from the ground, resulting in a 13 million megaton explosion. The other scenario was a 3 kilometer diameter asteroid encountering weak ground resistance, releasing 0.5 million megatons of TNT energy.

In simulations, both scenarios resulted in a crater 110 kilometers across, triggering a megatsunami that traveled up to 1,500 kilometers from the impact site – easily covering the region around Maja Valles.

The simulations also matched the boulder-strewn landscape, as material ejected from the impact was carried and deposited by the tsunami, which in the case of the 3-kilometer asteroid, reached a height of 250 meters.

“Our simulated impact-generated megatsunami events match the mapped margins of the oldest megatsunami deposit and predict fronts hitting the Viking 1 landing site,” the researchers wrote.

“The location of the region along a lobe facing upland aligned with erosional fissures supports a megatsunami origin.”

The site is analogous to the Chicxulub impact, the researchers said.

Both occurred in a shallow marine environment, created a similarly sized temporary cavity in the ground, and (according to the simulations) generated a tsunami more than 200 meters high.

“Our findings,” they wrote, “support the idea that rocks and soil salts at the landing site are of oceanic origin, inviting scientific reconsideration of information collected from the first in situ measurements on Mars.”

The research was published in the journal Scientific Reports🇧🇷

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