About 3.4 billion years ago Mars had an atmosphere and oceans. A really big asteroid hit causing a megatsunami. Over 1200 feet high!

Ancient killer asteroid created a megatsunami on Mars


Within the Solar System, Mars and Earth are two sibling planets with similar early histories, but very different recent ones. In the early stages of the Solar System, both worlds:

  • survived giant, early impacts,
  • gained moons that persist until the present day,
  • possessed temperate surface conditions and substantial-but-thin atmospheres,
  • had copious amounts of liquid water on their surfaces,
  • and the right overall conditions — as far as we know them — for life to arise for over 1 billion years.

However, from an evolutionary perspective, these two worlds then rapidly diverged. Here on Earth, life went on to transform our biosphere and persisted and thrived ever since, while on Mars, the red planet lost its core dynamo, then its magnetic field, and then its atmosphere and liquid oceans.


But before that, some 3.4 billion years ago, a killer asteroid landed in the Martian oceans, creating a 110 kilometer-wide crater and a megatsunami more than a quarter-mile (~450 m) high, sending boulder and other impact debris more than 1500 kilometers away from the collision site. At last, theory and observation have come together to complete the story, shedding a new light on a Martian catastrophe that occurred billions of years ago, back when liquid water oceans covered the red planet.

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The evidence for a watery past on Mars — once hotly disputed — is now overwhelming, with sedimentary rock, dried-up riverbeds with oxbow bends in them, and even salt-rich deposits and hematite spheres found in many locations on the surface. The evidence for these ancient oceans, however, wasn’t known at the time we first landed on the Martian surface. Nonetheless, what we found on the surface during that first mission, Viking 1, came as a tremendous surprise to those scientists who specialized in the study of Mars.

It had been known, even before Viking 1 landed, that the landing site it was headed to was going to be close to the end of a very large flood channel: Maja Valles. What scientists had expected to find was a geological record of an ancient megaflood, with the sorts of deposits we find on Earth wherever floods occurred in the past. Things like boulders embedded in deposited sediment and streamlined islands were the anticipated features.

But that wasn’t what was present at all. Instead, there was a large abundance of boulders strewn all about, atop a plains-like structure. This doesn’t add up, but whenever there are features present that you can’t explain, that’s a strong hint that you’ve got a scientific mystery just waiting to be solved on your hands.

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It’s now been more than 45 years since the Viking 1 landing took place, and in a fascinating new paper out in Nature Scientific Reports, the authors claim to have found a potential solution. Perhaps the Viking 1 lander site was located at or near the edge of the ocean/continental borders late in the game: when Mars still possess oceans on its surface, but after this megaflood, caused by Maja Valles emptying, occurred. If a large-enough impact hit the Martian ocean — similar to the famed impactor that hit Earth some 65 million years ago — a combination of crater ejecta and an associated megatsunami could be a potential solution.



The thing that had been missing, up until now, was the identification of the crater that could have been responsible for that. Just as the discovery of Chicxulub crater on Earth, along with the layer of iridium-enriched ash found at the K-Pg boundary, validated and confirmed the picture that an asteroid triggered our planet’s 5th great mass extinction since the dawn of the Cambrian explosion, the discovery of crater Pohl, highlighted in the image above, might just be the piece of evidence that tips the scales in favor of a long-ago giant impact on Mars.


]The crater Pohl is remarkable in a number of ways. It is:

  • 110 kilometers in diameter, making it a large impact crater,
  • located within the northern lowlands in an area suspected to be covered in ocean before Mars dried up,
  • in a region suspected to be in the ocean shallows, roughly 120 meters below sea level at the time,
  • and appears to be located about 900 kilometers from the Viking lander site.

The next step in validating this picture — which the authors also undertook — was to perform simulations that modeled asteroid and comet collisions on an early, wet Mars, and to see what sort of phenomena ensued.

the study found[ was that there were multiple models that fit the observed data, dependent on whether the ground strongly or weakly resisted the impact that occurred. In both cases, the impact would have occurred about 3.4 billion years ago: before Mars lost its oceans, but after many of the ancient events that led to a megaflood-generated ocean. In both instances, an asteroid would be the culprit, with the size of the asteroid varying from 3-to-9 kilometers and the total impact energy varying from 0.5 to 13 million megatons of TNT equivalent.

What was remarkable about these simulations — at least to me, as a scientist looking on who doesn’t specialize in this area — is that they both indicated a remarkable, fast-propagating tsunami would have formed: unlike any other in scope or scale ever considered on the Martian surface. As you can see from the graphs below, the wave would have reached a maximum height of between 400 and 500 meters (more than a quarter of a mile) above sea level, including rising more than 200 meters above normal onto dry land. In just hours, the Viking 1 landing site would have been submerged, and elsewhere, the megatsunami would have reached over 1500 kilometers from the impact site.This leads to a remarkable story for how the Viking 1 lander site came to possess the features it now has. First, Mars flooded, creating the ocean that covered the low-lying northern hemisphere of the planet. Second, an energetic impact between an asteroid and Mars occurred, creating both ejecta and a tsunami so large, it’s classified as a megatsunami. Third, the megatsumani carries some of that material up high onto the continental shores, depositing it as it recedes.