Giant asteroid triggered devastating Martian megatsunami, evidence shows: ScienceAlert

Several sources of data suggest that March has not always been desiccated dust bowl it’s today.

In fact, the Red Planet was once so wet and slippery that a megatsunami was unleashed, crashing into the landscape like a water disaster. What caused this devastation? According to new research, a giant asteroid impact, comparable to the Chicxulub impact 66 million years ago – the one that killed the dinosaurs.

Researchers led by planetary scientist Alexis Rodriguez of the Planetary Science Institute in Arizona have located a huge impact crater which they believe is the most likely origin of the mystery wave.

They named it Pohl and located it in an area eroded by catastrophic flooding, which was first identified in the 1970s, on what may be the edge of an ancient ocean.

When NASA Viking 1 probe landed on Mars in 1976, near a large flood channel system called Maja Valleshe found something strange: not the expected characteristics of a landscape transformed by a mega-flood, but a plain strewn with rocks.

A team of scientists led by Rodriguez determined in a 2016 paper that it was the tsunami wave resultlargely resurfacing the shore 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 have led scientists to Lomonsov crater as the source of the latest tsunami.

However, the source of the previous tsunami remained elusive. The northern plains in which a Martian ocean is thought to have lapped are heavily cratered and difficult to interpret. Rodriguez and his team painstakingly combed through maps of the surface of Mars, looking for impact craters that could be linked to huge tsunamis.

They hit Pohl, located about 900 kilometers (560 miles) northeast of Viking 1’s landing site, a crater 110 kilometers in diameter, located about 120 meters (394 feet) below what scientists believe to have been sea level, in a region called the Chryse Planitia.

Topographic map showing crater background and landing site. (Rodriguez et al., Science. Representing., 2022)

Based on rocks around the crater that had previously been dated to around 3.4 billion years ago, the researchers speculated that Pohl too may have formed around this time. And its position near flood-eroded surfaces and hypothetical megatsunami deposits suggests the crater was formed during a marine impact.

To confirm their suspicions, the researchers performed impact simulations, adjusting the parameters of the impactor and the surface on which it struck. They found two scenarios suitable for the observed site.

First, an asteroid 9 kilometers (5.6 miles) in diameter encountering strong ground resistance, resulting in a 13 million megaton explosion. The other scenario was a 3 kilometer diameter asteroid encountering low ground resistance, releasing 0.5 million megatons of TNT energy.

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

The simulations also matched the rock-strewn landscape, as ejecta from the impact were 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 momentum closely matches the margins of the mapped older megatsunami deposit and predicts fronts reaching the Viking 1 landing site,” researchers write.

“The location of the site along an upland-facing lobe aligned with erosional grooves supports a megatsunami origin.”

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

Both occurred in a shallow marine environment, created a similar sized temporary cavity in the ground, and (according to simulations) generated a tsunami over 200 meters in height.

“Our Discoveries,” they write“allow the rocks and soil salts of the landing site to be of marine origin, inviting a scientific reconsideration of the information gathered from the first in situ measurements on Mars.”

The research has been published in Scientific reports.

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