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[♪ INTRO] Mars is often thought to be a cold, dead hunk
of rock.
No liquid water, no geologic activity, and no
life, unless you count that rover that sang itself Happy Birthday.
But over the past few years, we’ve realized that’s
not entirely true.
The red planet has quakes, and according to a paper
published this week in Nature Astronomy, there might be
molten rock churning beneath the Martian crust, too.
On Earth, most of our volcanic and seismic activity
happens where two tectonic plates smush up against
each other, like the Ring of Fire that borders much of
the Pacific Ocean.
But thanks to mantle plumes, hot columns of rock
that bubble up from deep within the Earth, we can get
volcanic and seismic activity in places like Hawaii, smack
dab in the middle of that ocean.
The volcanoes that form atop mantle plumes are known as hotspot volcanoes.
And one of them, Mauna Loa, recently started erupting
after a 38-year nap.
Meanwhile, over on Mars, the last last known volcanic eruption was somewhere between
53,000 and 210,000 years ago.
Now, the heyday of Martian volcanism ended over three billion years ago, and for most
of the time humans have been exploring Mars, we have thought of it as geologically dead.
But in 2018, NASA’s InSight mission delivered a seismometer to the planet’s surface.
And at least in the region known as Elysium Planitia, the ground has spent the past four
years quaking beneath InSight’s proverbial feet.
But since Mars hasn’t displayed much evidence of tectonic plate activity, maybe mantle plumes
are to blame.
That’s where this new research comes in.
A group of scientists from the University of Arizona dove into a bunch of data that
decades of previous research had collected.
And based on all the evidence, the team argues there is only one explanation for all of the
features in the area, including Elysium Planitia’s elevation compared to the surrounding lowlands,
the strength of the gravity in that region, and the seismic patterns that InSight was
recording.
There’s an active mantle plume, bubbling up rock like a planet-sized lava lamp, and
it’s hiding underneath a system of fissures called Cerberus Fossae.
These fissures were formed by past tectonic activity, and they just so happen to be the
location of Mars’s most recent volcanic eruption all those millennia ago.
So this claim isn’t completely out of the blue.
However, more evidence is needed before anyone can say there definitely is an active mantle
plume down there.
If we can find it, Mars will become the third place in the inner solar system that we know
has active mantle plumes, after Earth and Venus.
Or has at least one mantle plume.
But that’s all Mars needs for us to learn that a planet we thought was completely dead
has just really mellowed out in its old age.
Speaking of volcanoes, there’s another natural disaster in Mars news this week.
According to research published last week in Scientific Reports, scientists may have
found the source of an ancient megatsunami.
Modern Mars might be a planet-wide desert, but scientists have suspected for decades
that Past Mars was a completely different story.
In 1972, the Mariner 9 spacecraft spotted what looked to be ancient flood channels near
the Martian equator.
A long time ago, on the planet next door, Mars’s surface was partially covered in
liquid water.
So it made sense to send a lander there and do a bunch of follow-up science.
But when the Viking 1 lander arrived in 1976, it didn’t find the smooth landscapes scientists
expected to see from all that flooding.
Instead, the lander sent back photos of a whole bunch of boulders.
At the time, scientists couldn’t figure out where these boulders came from, but in
2016, one team suggested that they were left behind by a megatsunami 3.4 billion years
ago.
A big wave of water could certainly deposit a bunch of rocks from one part of Mars to
another.
But tsunamis don’t just happen.
Something must have set it off.
The authors of that 2016 paper thought the most probable cause was an asteroid or comet
impact.
And that impact would leave behind a massive crater, even if it got worn down due to the
ravages of time.
Someone just needed to find it.
So some of those authors teamed up with some other scientists for a new study.
After analyzing images of the planet’s surface near the original Viking 1 landing site, this
team identified a crater 900 kilometers away that looked big enough to have been accompanied
by a megatsunami.
It’s called Pohl crater, named after a Science Fiction author.
It’s about 110 kilometers wide, and based on the location and neighboring rock layers,
it appears to be just the right age, too.
3.4 billion years ago, this part of Mars is thought to have been
covered by a big, deep ocean.
The ideal location to trigger a massive tidal wave with an asteroid impact.
So the team simulated different collisions to see what kind of impact could have not
only formed Pohl crater, but also caused a megatsunami powerful enough to carry boulders
to the Viking 1 landing site.
They found that the crater was likely formed by either a 9 kilometer asteroid hitting hard
ground and encountering a lot of resistance, or a 3 kilometer asteroid crashing into more
brittle ground.
They determined that the second scenario was a better fit to the geologic record.
And while both impacts caused tsunamis that could correctly restructure the coastal areas,
a larger asteroid hitting stronger ground would have
caused extra flooding beyond where the record suggests.
In the 3 kilometer, brittle ground simulation, the resulting
wave would have been about 250 meters tall when it
moved onto land.
And if all this sounds vaguely familiar to you, that might be because this impact has
a lot in common with a rather famous event on Earth.
Around 66 million years ago, an asteroid crashed into
the water just off the coast of the Yucatan peninsula.
It left behind a 110 kilometer wide crater roughly 200 meters below
sea level, and caused a tsunami around 200 meters tall
on land.
And it also helped kill off the non-avian dinosaurs, which
we don’t think were on Mars, so that’s a difference.
But it’s possible that water the asteroid smashed into
had evolved some kind of life.
Scientists will just have to keep up the search.
And one day, maybe we’ll discover that the Mars of
today is more than just geologically alive.
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[♪ OUTRO]