[♪ INTRO]
We’ve been looking up and trying to understand Mars for hundreds of years.
But despite orbiters, probes, landers, and rovers,
there are still mysteries on the Red Planet waiting to be solved.
Among them are strange, flowing features around some of its craters,
which don’t seem to fit with Mars’s modern-day, dusty image.
But some scientists have seen craters here on Earth that shed light on this,
dating back to the impact that killed the dinosaurs.
Typically, when an asteroid or a comet hits a celestial body,
the impact energy is enough to make a crater.
The stuff that’s thrown out of the crater is known as ejecta.
And if there’s enough of it, it will spread around the crater to create an ejecta blanket.
When we look at the ejecta around craters on bodies like the Moon and Mercury,
we see a kind of dusty ring smoothly surrounding the crater
and petering out with distance.
The effect is the same as if you had dropped something into loose sand.
The material in the middle would fly out on a ballistic trajectory,
moving up and out until gravity pulled it back down.
But on Mars, the ejecta blankets around some craters are very different.
Instead of smoothly surrounding the crater in uniform rings,
they seem to have multiple layers, with wavy,
lobed edges that extend farther in some places than in others.
And at the edges, there are ejecta ramparts.
Basically, instead of the ejecta blanket tapering out with distance,
there’s a raised rim of material at the very far edge.
In the 1970s, scientists suggested these features
could be produced by the ejecta flowing along the surface.
If ejecta were flowing close to the ground, the lobe shapes could be created
when the flow traveled farther in some places.
And the ejecta ramparts could form as the flow lost energy
and material piled up at the end.
As for how that might actually happen, scientists have come up with
two possible explanations based on experiments and modeling:
One is that, when an asteroid or comet strikes the surface,
volatiles like ice and water within the Martian crust are released.
They mix with the rocky ejecta and create a lubricated debris flow that
flows a bit like volcanic mudflows on Earth.
The other idea hypothesizes that it’s a gaseous debris flow of dry ejecta,
similar to terrestrial pyroclastic flows of volcanic gas, ash,
and rock fragments that move at high speeds down volcanic slopes which creates
a low, rolling, turbulent cloud of debris that surges across the surface.
The problem is, modern-day Mars is notoriously dry and practically airless,
so these hypotheses imply different conditions than what we have today.
We don’t know which, if either, is correct.
So far, all of the studies and hypotheses of these so-called
fluidized ejecta blankets on Mars have been based on orbiter images.
And there’s only so much a picture from hundreds of kilometers away
can tell us about if Mars’s water and thick atmosphere
were responsible for the fluidized ejecta.
One solution could be to look at ejecta blankets on Earth,
since we’ve also been hit by our fair share of asteroids.
But Earth’s surface is much more dynamic than Mars’s,
so ejecta blankets are soon eroded away or covered by new sediments.
However, in the 1990s, scientists uncovered ejecta sites
around the Chicxulub crater on the Yucatan peninsula in Mexico.
Chicxulub measures about 180 kilometers across,
and has long been recognized as the crater left from
the impact that killed the dinosaurs 65 million years ago.
These ejecta sites were discovered hundreds of kilometers away from Yucatan,
in Belize and elsewhere in Mexico, but it soon became apparent that
they contained ejecta from that same, massive impact.
In fact, this newly discovered ejecta blanket was
buried under more recent sediments,
but extended over an area up to five crater radii from the center.
That’s much bigger than was expected for ballistic ejecta based on
similar craters observed on the moon, so the researchers concluded that
this was in fact a huge, fluidized ejecta blanket like the ones on Mars.
Even going on 30 years later, it’s one of the largest and most well preserved
of its kind discovered on Earth, and it’s perfect for studying
fluidization processes up close.
Upon further examination, geologists found that this ejecta blanket was
composed of several layers, which seemed to have been laid down in different ways.
Smooth, laminar layers looked like mudflows that had slid along the surface.
And jumbled-up layers suggested more churned-up, turbulent flows.
In other words, there were signs of both
volatile-rich surface flow and gaseous turbulent flows.
That’s not surprising, since Earth has water-rich rocks
beneath the surface and a thick atmosphere.
But it lends support to the idea that the similar ejecta blankets on Mars could also
have been created by a combination of water-rich rocks and atmospheric turbulence.
And scientists were able to learn even more
about this event by creating a model based on their observations.
For Chicxulub, they think that ejecta flew on a ballistic trajectory,
but was then overtaken by a fast, turbulent,
atmospheric flow that moved radially outwards from the crater rim.
Shortly after, a wet flow moved over the ground, diverted around the local hills,
eroded some of what was already deposited,
and left behind the layered, partly eroded ejecta blanket we see today.
This kind of model is invaluable for understanding the fluidization of ejecta on Mars.
Scientists can now look for specific features in orbital images,
or in closer rover studies to assess the roles of both volatile-rich surface flow
and gaseous turbulent flow mechanisms.
For example, diverted flows and eroded material
could be signs of slower volatile-rich surface flows.
So, even though Mars is now dry and dusty and pretty much airless,
the fluidized ejecta blankets are a remnant of a time
when the Red Planet was much more like Earth.
Sometimes, we can learn a surprising amount about our planetary neighbors
by looking down, instead of up!
And speaking of looking up, we’ve taken it upon ourselves to immortalize
a little Mars lander, Mars 3 as May’s Pin of the Month!
If you want this little guy for your own, we will be taking pre-orders
throughout the month, and then we’ll ship at the end of the month.
But be sure to order before the end of May,
because we will never make more of this pin again!
Instead, next month, we’ll share a new space pin for you to enjoy.
So check it out by clicking on the link below , and thank you for your support!