© AP Photo / NASA/JPL-Caltech/MSSS
About 4.5-3.5 billion years ago, Mars is believed to have had an active surface hydrosphere. At the time, the northern plains of the planet were covered by a salty ocean with a volume up to 15-17 million km³, comparable with the current state of the Arctic Ocean.

A team of planetologists led by Alexis Rodriguez, a researcher at the Institute of Planetology in Tucson, US, have discovered a previously unknown crater on the surface of the Chryse Planitia, whose formation about 3.4 billion years ago generated a powerful tsunami wave. The asteroid that caused it was comparable in size to the meteorite that destroyed the dinosaurs, scientists wrote in an article in the journal Scientific Reports.

Much to the surprise of planetary scientists, the first images of the Maya Valley from Viking 1 lacked the typical landform features associated with floods which had been expected, including lined deposits of rocks and drop-shaped accumulations of sand and clay. Instead, photos of the "Mayan valleys" showed plains covered with a number of large cobbles.

Rodriguez and his colleagues discovered that one of these tsunamis actually existed, and scientists also discovered its source - the previously unknown 110-kilometer-long crater Pohl, located inside lowlands 900 km northeast of the Maja Valles. It resulted from the impact of a 10-12 km asteroid about 3.4 billion years ago, when the surface of Mars was still covered by oceans.

The fall of an asteroid into one of these oceans resulted in an explosion and the formation of a mega-tsunami whose waves reached a height of 250 meters by the time they reached shore.

"Our simulated impact-generated megatsunami run-ups closely match the mapped older megatsunami deposit's margins and predict fronts reaching the Viking 1 landing site," the researchers write. "The site's location along a highland-facing lobe aligned to erosional grooves supports a megatsunami origin. Our findings allow that rocks and soil salts at the landing site are of marine origin, inviting the scientific reconsideration of information gathered from the first in-situ measurements on Mars."

In this respect, the Martian tsunami was comparable in effect to those events that occurred on Earth 66.5 million years ago when dinosaurs went extinct. This makes the Pohl Crater and its surroundings particularly interesting to the study, the scientists concluded.