“Imagine this enormous red wave coming towards you, up to 120 meters high,” said Alexis Rodriguez, a Mars researcher at the Planetary Science Institute of a mega-tsunami on Mars 3.4 billion years ago with skyscraper-high waves created when giant meteoroids slammed into a frigid ocean covering Mars’s northern hemisphere leaving a 75-mile-wide impact scar. “It would have been pretty spectacular.”
A new study, published last month in the Journal of Geophysical Research suggests that the impact scar is to the red planet what the Chicxulub crater is to Earth: the mark of a meteor that generated a mega-tsunami when the planet was relatively young. If accurate, the finding adds evidence to the hypothesis that Mars once had an ocean, and would have implications for our search for life there reports Robin George Andrews in New York Times Science.
On a world believed to have lacked Earth-like plate tectonics, any tsunamis were probably triggered by a meteor slamming into a huge body of water. Growing evidence that tsunami waves washed over the boundary between the southern highlands and northern lowlands strengthens the conjecture.
In 2017, a team led by François Costard, a planetary geomorphologist at the French National Center for Scientific Research, used computer modeling to reproduce the mega-tsunamis most likely to have created those thumbprint terrains narrowing it down to the Lomonosov crater in the planet’s northern plains (image above). It fits the bill as the source of tsunami deposits identified on the surface. The 120km-wide bowl was called Lomonosov, after the 18th Century Russian polymath Mikhail Vasilyevich Lomonosov. The feature is extremely degraded today, with a collapsed crater rim.
Two successive waves were formed during the event, says Costard. “It was a really large-scale, high speed tsunami. At the very beginning, a crater of 70km in diameter was created by the impact. This expelled a huge volume of water, with wave propagation at 60m/second,” he explained.
“The initial wave was about 300m in height. After just a few hours, that tsunami wave reached the palaeo-shoreline located at a few hundred km from the impact crater.”
This monster wave washed over hills and plateaus and through valleys, leaving behind the lobate flow deposits. “Finally… due to the Martian ocean filling in that crater, which produced a kind of rebound, there was a second wave propagation,” Costard added.
A window into the habitability of Mars
If there was an ocean on Mars three billion years ago, it could have made the Red Planet a more hospitable place for life, raising hopes that signs of biology could be detected today. “If we do have this evidence of a tsunami having occurred back three billion years ago, there must have been an ocean present in the northern plains,” said co-author Steve Clifford with Planetary Science Institute in Houston.
“It’s very hard to conceive of any other process other than a tsunami that could have emplaced these lobate deposits along the dichotomy boundary,” Clifford told BBC News of the dichotomy between the northern hemisphere and southern hemisphere of Mars. “There is ambiguity in all the various lines of evidence that have been cited regarding whether Mars is water-rich or water-poor. But the morphologic evidence that’s been presented here is a very persuasive case for a water-rich planet.”
Rodriguez, co-author of the new study, said the remnants of this Martian ocean may be a good target in the search for evidence of life on the red planet. In the 2017 study, Exploring the Tsunami-Battered Coasts of Planet Mars presents new evidence that reawakens old hypotheses. The question of whether the red planet may have once been blue surfaces again with the discovery of evidence supporting ancient tsunamis on Mars.
This is of particular interest to NASA Ames as it is invested in uncovering evidence of water on Mars an essential step along the way to supporting extraterrestrial life. Rodriguez, elaborated that the Lomonosov crater containing tsunami deposits could serve as a leading candidate for a landing site to search for evidence of Martian life.
The ocean may have been fed by catastrophic floods from underground caches of liquid water. If so, sediments in the north “may be a window into the subsurface habitability of Mars,” Rodriguez said. If they contain geochemical signatures of ancient microbiology, then the liquid aquifers thought to exist beneath Mars’ surface may still be reservoirs for life today.
Scientists don’t have unambiguous proof of a northern ocean
This one of the “core paradoxes” of Martian planetary science, says Rodriguez.
Paul Byrne, a planetary geologist at North Carolina State University who was not involved with the study, the New York Times reports, agreed: “It’s fair to say that we don’t yet fully understand the history of Mars’s climate, and certainly, the climate models we use will continue to be improved. So the climate models might not be wrong,” he added — but more data is needed to say one way or the other.
Nearly half a century ago the Mariner 9 spacecraft returned images of some of the largest channels in the Solar System. Orbital observations of the gigantic channels suggested they were formed approximately 3.4 billion years ago by cataclysmic floods, much larger than any known to have occurred on Earth. The prospect that abundant flowing water once sculptured the Martian landscape ignited renewed interest in the possibility that life may have once thrived on the planet.
To test the Martian mega-flood hypothesis, NASA deployed its first Martian rover; the Sojourner, on board the 1997 Mars Pathfinder spacecraft that journeyed to the red planet. NASA spent a total of $280 million on the mission, including the launch vehicle and mission operations. The terrain within the rover’s visual range includes potential fluvial features suggestive of regionally extensive flooding. However, those features suggest floods that were at least 10 times shallower than those estimated using images obtained from orbit. Hence, the mission was not able to exclude still disputed alternative views sustaining that debris or lavas flows could have in fact dominated the channels’ formational history without significant water discharges.
“Our paper shows a basin, with roughly the surface area of California, that separates most of the gigantic Martian channels from the Pathfinder landing site. Debris or lava flows would have filled the basin before reaching the Pathfinder landing site. The very existence of the basin requires cataclysmic floods as the channels’ primary formational mechanism” said Rodriguez.
“The basin is covered by sedimentary deposits with a distribution that precisely matches the inferred extent of inundation from potential catastrophic floods, which would have formed an inland sea,” Rodriguez said. “This sea is approximately 250 kilometers upstream from the Pathfinder landing site, an observation that reframes its paleo-geographic setting as part of a marine spillway, which formed a land barrier separating the inland sea and a northern ocean.
“Our simulation shows that the presence of the sea would have attenuated cataclysmic floods, leading to shallow spillovers that reached the Pathfinder landing site and produced the bedforms detected by the spacecraft,” Rodriguez said.
The team’s results indicate that marine spillover deposits contributed to the landscape that the spacecraft detected nearly 22 years ago, and reconcile the mission’s in situ geologic observations and decades of remote-sensing outflow channel investigations.
The sea bears an uncanny resemblance to the Aral Sea on Earth in that in both instances they lack distinct shoreline terraces. Its rapid regression over shallow submerged slopes resulted in rates of shoreline front retreat too fast for the terraces to form. The same process could partly account for the long-recognized lack of northern plains shorelines.
“Our numerical simulations indicate that the sea rapidly became ice-covered and disappeared within a few thousand years due to its rapid evaporation and sublimation. During this time, however, it remained liquid below its ice cover,” said PSI Senior Scientist Bryan Travis, a co-author in the paper.
“Unlike on Earth, this sea was likely groundwater fed. If the ancient source aquifers hosted life, the proposed marine sedimentary materials at the Pathfinder landing site might contain a record of that life, a location easily accessible by future missions,” Rodriguez said.
“An exciting observation is that the inland sea and the previously proposed northern plains ocean share a maximum paleo-shoreline elevation, implying a subsurface connection, perhaps through conduits, between the two marine bodies soon after they formed. This elevation match forms a new powerful observation that strongly favors the northern ocean hypothesis,” said PSI Senior Scientist Dan Berman, a co-author in the paper.