There is a strong case to be made that Mars wasn't once the dried-up wasteland it is now.
In fact, the red planet used to be so wet and sluggish that a
megatsunami broke loose and swept across the terrain like a flood of water.
What resulted in this destruction? New study suggests that the dinosaurs were
wiped off by a massive asteroid impact similar to the Chicxulub impact that
occurred on Earth 66 million years ago.
The Planetary Science Institute in Arizona's research team,
led by planetary scientist Alexis Rodriguez, has discovered a sizable impact
crater that is thought to be the mystery wave's most likely source to date.
They gave it the name Pohl and discovered it in what might
have been the edge of an ancient ocean, in a region that had been devastated by
catastrophic flood erosion and was first discovered in the 1970s.
When NASA's Viking 1 probe touched down on Mars in 1976, it
discovered something peculiar: a boulder-strewn plain instead of the features
expected of a landscape transformed by a megaflood.
In a 2016 publication, a group of scientists led by Rodriguez
concluded that this was caused by tsunami waves, which significantly resurfaced
the shoreline of an ancient Martian ocean.
At the time, they proposed that two tsunamis occurred 3.4 and
3 billion years ago as a result of distinct impact events. Scientists
discovered the Lomonsov crater as the tsunami's later source thanks to
numerical simulations.
The earlier tsunami's origin, though, remained a mystery. A
Martian ocean is assumed to have previously sloshed on the northern plains,
which are extensively cratered and difficult to understand. Rodriguez and his
colleagues laboriously looked through maps of the surface of Mars in search of
impact craters that may be connected to enormous tsunamis.
They discovered Pohl, a crater measuring 110 kilometres in
diameter and sitting about 120 metres (394 feet) below what researchers believe
would have been sea level in a region known as the Chryse Planitia, about 900
kilometres (560 miles) northeast of the Viking 1 landing site.
The scientists hypothesised that Pohl may have formed at the
same time as the crater based on rocks around the crater that had previously
been dated to about 3.4 billion years ago. The crater likely formed from a
maritime impact based on its proximity to surfaces that have been eroded by
floods and deposits from potential megatsunamis.
The researchers ran impact simulations, adjusting the
impactor's and the surface it collided with to corroborate their assumptions.
They discovered two possibilities that explained the reported location.
First, a 13 million megaton explosion was caused by an
asteroid that was 9 kilometres (5.6 miles) large and encountered substantial
ground resistance. The alternative scenario had a 3 km wide asteroid
encountering negligible ground resistance and ejecting 0.5 million megatons of
TNT energy.
Both of these scenarios produced craters in the simulations
that were 110 kilometres across and that caused megatsunamis to spread as far
as 1,500 kilometres from the impact site, easily covering the area around Maja
Valles.
The tsunami, which in the case of the 3-kilometer asteroid,
reached a height of 250 metres, transported and deposited the ejecta from the
impact, matching the boulder-strewn terrain as it did so.
Our predicted fronts reaching the Viking 1 landing site and
our modelled impact-generated megatsunami run-ups closely match the borders of
the documented earlier megatsunami deposit, the researchers write.
"A megatsunami origin is supported by the site's
location along a highland-facing lobe aligned to erosional grooves."
According to the experts, the location is comparable to the
Chicxulub impact.
Both took place in a shallow marine environment, produced a
temporary cavity in the ground that was roughly the same size, and (according
to simulations) produced a tsunami that was over 200 metres tall.
Our research "allows that rocks and soil salts at the
landing site are of marine origin, inviting the scientific reconsideration of
data gathered from the first in-situ measurements on Mars," the
researchers write.
Scientific Reports has published the study's findings.
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